Edu System Handbook Jan73

EduSystemHandbookJan73 EduSystemHandbookJan73

User Manual: EduSystemHandbookJan73

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ADDITIONAL COPIES
Additional copies of this handbook may be purchased for $5.00
per copy. Please send your order to the address below. DEC offers
special discounts on quantity orders.
Digital Equipment Corporation
Communications Services, Parker Street
Maynard, Massachusetts 01754

prepared
by
.
small systems technical writing group
programming department
digital equipment corporation

pdp-s handbook series·

FIRST PRINTING, JANUARY 1973
The description and availability of the software products de..
scribed in this manual are subject to change without notice. The
availability or performance of some features· of the software products may depend on a specific configuration of equipment. Consequently, DEC makes no claim and shall not be liable for the
accuracy of the software products. Distribution of software products shall be in accordance with the then standard policy for each
such software product.
Copyright © 1973
Digital Equipment Corporation
The following are registered trademarks of Digital Equipment
Corporation~ Maynard, Massachusetts:
FOCAL
OS/8
PDP
RSTS

DEC
DECtape
Digital
EduSystem

ERROR REPORTING
If you find any erro!s in this handbook, or if you have any

questions or comments concerning the clarity or completeness oL
this handbook, please direct your remarks to:
Digital Equipment Corporation
Software Information Service, Building 3-5
Maynard, Massachusetts 01754

The computer is an exciting contemporary piece of equipment.
This fact alone explains some of the fascination that a comp~ter
invariably stirs up among students, but it doesn't explain all of it.
The powerful motivational capabilities which the computer demonstrates in every school that. installs one can only be explained
by the way it is used.
The computer is tireless. Unlike a student, it loves to do complex calculations. Separating theory from calculation in school
assignments has always been a problem. Some of the most interesting and challen·ging concepts of math and science involve,
unfortunately, an overwhelming amount of dull calculations. The
student gets bogged down in the" arithmetic and never gets excited about the idea. Or, worse still, a less important concept is
taught because its calculations come out even. The computer, by
taking on all calculations and doing them quickly and accurately,
opens up new possibilities for classroom study and student interest.
The computer is immediate and unfailingly accurate. It does in
seconds what people take minutes or hours to do. The speed of
its responses make for powerful reinforcement. It challenges the
student to think through the concepts as fast as it grinds through
the calculations.
The computer is anonymous. Real learning occurs when a student has an idea and tries it out. At the start, he isn't sure whether
the idea is valid. Some students have no fear of being wrong and
will tell the class their idea. Others are less willing to risk the
ridicule of being wrong; The computer lets all students tryout
their ideas and gain confidence in them. It treats all students alike;
it has no favorites. It waits for the slower user and bounds ahead
quickly for the brighter student. With a computer, a student competes with his past achievements, not with other students.
Above all else, the computer is challenging. Why is it that a
student who quits on a homework problem after trying it once
will work tenaciously to get a program running right? Partly, it's
iii

the immediacy of the computer's response. Partly, it's the ease
with which the student can change his program and try again.
Partly, it's the fun of talking to·a machine and having it respond.
But beyond aU that, there is something about the close interaction
between a user and a fast, willing, logical machine which is tremendously challenging.
In all these ways and more, the computer stimulates the student,
stretches his thinking, provides an immediate andpertinent,application for skills learned in class. The impact on the teacher can
be just as great as the impact on the student. Given motivated
students, the dedicated teacher becomes even more dedicated. It
is not unusual for a teacher to stay at school until five o'clock to
give students more time on the computer.
Computers have other uses around the schoo~ than instruction.
For example, a computer can easily be programmed to grade tests,
thereby saving precious teacher time, as well as providing more
immediate feedback to students. Other tedious administrative
chores such as attendance reporting, grade reporting, transcripts,
and payroll can be performed on the computer.
What will the computer mean in your school? Almost cert~inly
it will mean that students learn and improve at a faster rate. Tests
have shown that students who use the computer as part of their
math class improve at four times the rate of those who are taught
in the traditional way-not just honor students, not using a
futuristic curriculum. A cross-section of students-black, white,
Chicano, disadvantaged, rich, middle-class-in regular algebra
classes improved four times as fast with the computer. The computer also means more thorough understanding coupled with tremendous student motivation. It means more dedicated teachers
and an erasing of tedious administrative chores. It means contemporary education for today's world.
The computer does not replace the teacher. Nor does the simple
existence of the computer make a poor student into a superior
student. But in school after school, the computer is turning the
bored, lethargic student into an involved, eager student. We at
Digital believe that this is the vital, first step to better education.
And we firmly believe that computers are for all kids, not for a
few geniuses.
IV

EDUSYSTEMS-SCHOOL COMPUTERS THAT
MEET THE CHALLENGE
It takes more than just hardware to make an effective school
computer system. It takes a thoroughly tested combination of
system components and instructional materials designed specifically for classroom use. Recognizing this fact, Digital Equipment
Corporation has designed EduSystems-a complete line of computer systems tailored to the needs of schools and colleges.
The basis of each EduSystem is. a PDP-8/E computer,l a terminal, and a BASIC language processor. All EduSystems utilize
the well-known computer language BASIC. BASIC programs are
simple combinations· of English words and decimal numbers.
Students with no previous computer experience can be writing
meaningful programs after as little as an hour of instruction.
EduSyst~ms are compact, trouble-free, and engineered for use
in the busy school environment. Even the largest EduSystem can
be installed and used right in the classroom. All systems can run
completely unattended (i.e., no operator is necessary). Each EduSystem is designed to handle a large number of student users.
Time-sharing allows up to 16 students and teachers to work at
the computer simultaneously. Batch processing allows hundreds
of student runs per day.
EduSystems are expandable; as school and student. needs in'crease, the configuration of the system may also increase. Starter
systems (EduSystems 5, 10, 15, and 20) grow to be Intermediate
Systems (Edl~Systems 25, 30; and 40); Intermediate Systems grow
1 Certain EduSystems are also availabJe on the PDP-l1 computer.
Write to the Educational Products Group, Building 5-5, Digital Equipment
Corporation, Maynard, Mass. 01754, for more information.

to be the Total System (EduSystem 50). The expansion modules
can be installed right at the school. Expandable EduSystems are
always the right size to meet a school's present demands. There is
never the need to start out with too much computer or end up
with too little.
As the EduSystem computer expands, so does the BASIC language. Digital's Total Systems2 offer the most powerful BASIC
language processors of any computers in their class. In addition,
EduSystem 50 provides time-shared FOCAL and FORTRAN-D
language processors, a time-shared Assembly Language package,
and system utility programs.
The effectiveness of EduSystems as classroom tools is well
proven. Hundreds of schools starting out with EduSystem 10 or
EduSystem 20 have since expanded to an Intermediate System, or
even a Total System, while many others are continuing to support
excellent programs of computer education without expanding their
facilities at all.
USING THE EDUSYSTEM HANDBOOK
The EduSystem Handbook provides a complete user's guide for
each individual EduSystem and a self-instruction course in the
use of the BASIC language in general. Most EduSystem users will
need to read only two' chapters of this handbook: Chapter 1, and
the chapter concerning the EduSystem being used.
Chapter 1 is a primer on the BASIC language, 3 allowing. the
user to teach himself the fundamentals of BASIC and to familiarize himself with the EduSystem terminal keyboard. Many examples
and exercises are included to aid the user in discovering the elements of the BASIC language. A user familiar with Chapter 1 can
write simple BASIC programs and run them on any EduSystem.·
Once the user knows the fundamentals of BASIC, he refers to
the chapter ( chapters 2 through 9) concerning his particular
EduSystem. The individual EduSystem chapters describe the features and extended capabilities of BASIC as it is used on the
specific EduSystem. Each chapter also contains detailed operating
instructions and error messages for the EduSystem. In addition,
EduSystem 80 is a Total System available only on the PDP-II.
Chapter 1 is derived from Teach Yourself BASIC, Volumes I and. II
published by Technica Education Corporation.
2

each chapter contains a table summarizing the BASIC language
capabilities of the EduSystem being described.
Chapter 9 provides' a detailed description of EduSystem 50 capabilities, not only of the BASIC language but also' of FOCAL,
FORTRAN-D, PAL-D (the assembly language), the EduSystem
50 Monitor, and all the system utility programs. The EduSystem
50 user will also find much helpful information in Introduction to
Programming and Programming Languages, Volumes 1 and 2 of
the PDP-8 handbook series.
The EduSystem Handbook is designed to serve as the primary
guide for users of all EduSystems. Users of each EduSystem will
find many programming examples to facilitate their understanding
of the system. A summary of the BASIC language capabilities of
all Digital EduSystems is provided at the end of Chapter 1.
, COMMON PROGRAMMING TERMS
Such words as loop, jump, nesting, and array have special
meanings to computer programmers. Familiarity with these terms
is a prerequisite to learning the more advanced programming
languages. The Index/Glossary at the end of this handbook defines
many of the commonly used computer programming terms.

vii

V11I

CHAPTER 1

TEAcH YOURSELF BASIC

1-1
Introduction
Teletype Keyboard .......................................................... 1-3
• • • tI • • • • • • • • • • • • • • • • • I

• • • • • • • • • • • • • • • • • • I '• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Getting Acquainted With BASIC .....................,...................
Numerical Expressions ....................... ,; ...........................
The PRINT Statement ................................. :..................
Floating Point Numerals ..................... ,....................... :.....
Printing Messages ....,.............................................. ...........
Exponents-Computing the Power of a Number ............

1-5
1-9
1-11

1-15
1-17
1-19

Gathering Speed ................................................ ~ .... '............. 1-20
Variables .................................................................... :..... 1-20
Variable Expressions .............. ;......... ~ ............................. 1-24
Feeding the Beast .................................. " ............................
The INPUT Statement ....................................................
The GO TO, Statement ................. .-..................................
READ and DATA Statements .........................................
The RESTORE Statement .................................. ............
More Messages ................................................................

1-26
1-26
1-30
1-32
1-36
1-37

'You Can Count on It ..........................................................
Loops ................................................................................
Loops Exposed .................................................................
FOR-NEXT Loops ... :......................................................
The STEP Clause ..... , ............................ ;.........................
Variable FOR Statements ...................................,.............
Extra for Experts ................................................... "........

1-39
1-39
1-41
1-45
1-50
1-52
1-55

'IX

Function Junction ................................................................ 1-57
The Integer (INT) Function ............................................ 1-57
The Square Root (SQR) Function .................................. 1-61
Finding Your Way .............................................................. 1-65
Flowcharts ...................................................................... 1-65
FOR...NEXT Loops in a Flowchart ................................ 1-71
Making Decisions ................................................................ 1-73
A Fork in the Road ........................................................ 1-73
The IF Statement ............................................................ 1-79
Varying Patterns .......................................... ,....................... 1-81.
Rectangular Patterns ............................................. ......... 1-81
The TAB Function .......................................................... 1-86
Meandering .......................................................................... 1-89
Random Numbers ............................................................ 1-89
Constellations .................................................................. 1-93
Little Boxes ........................................................................
Subscripted Variables ......................................................
Generalizing ............... '" . ...... ..... ... .... .... ... ...... ... ..... ....... ...
Variable Subscripts ..........................................................
Subroutines ......................................................................

1-97
1-97
1-1 01
1-102
1-105

Snoopy and the Red Baron ................................................
No Opinion ....................................................................
More Choices ..................................................................
Generation Gap ..............................................
Reprise ............................................................................

1-107
1-111
1-113
1-115
1-119

Kaleidoscope ........................................................................
Coin Tosser .......................................................... ..........
Dice ................................................................................
23 Matches ......................................................................
Rounding a Number ........................................................
Miscellaneous Math ........................................................
Say Something in Trigonometry ......................................
Do It Yourself Functions ................................................

1-123
1-123
1-124
1-125
1-127
1-128
1-130
1-131

..............

Past and Future BASIC ...................................................... 1-132
x

CHAPTER. 2

EDUSYSTEM 5

Introduction ....................... " .......... ~ ........... ,.............. ,........... 2-1
System Components .......................................................... 2-2
System Expansion ............................................................... 2-2
BASIC Language Capabilities .................................................
Line Numbers ........ ,.: ............................................................
Single-Character PRINT Command .... '..............................
Multiple Statements Per Line ............................................
Immediate Mode ..................................
INPUT Statement ......................................
'1 • • • • • • • • • • • • • • • • • • • • • • • • • • • • ,

1 •••••••••••••••••••••••

2-2
2-2
2-2
2-2
2-3
2-4

Program Editing ...................-........, .............. ~ ......~-................... 2-5
Error Messages ......................................... .............................. 2-5
Operating Instructions
Initial Installation .:............................................................
Turning Off the System .......................................................
Restarting the System ......................................................
Reloading the Functions ....................................................
Saving Programs on Paper Tape ........................................
Reloading Program From Paper Tape ..............................
It

CHAPTER 3

2-6
2;..6
2-9
2-9
2-9
2-9
2-10

EDUSYSTEM 10

Introduction ................................................ ............................ 3-1
System Components .......................................................... 3-1
System Expansion ............................................................ 3-2
BASIC Language Capabilities ........................... :..................
Line Numbers..................... ........... ........... .........................
Single-Character PRINT Command ..................................
MUltiple Statements per Line .................................'...........
Immediate Mode ..............................................................
INPUT Statement ,..............................................................

3-2
3-2
3-2
3-2
3-3
3-4

Program Editing ...... ,..... ~ ..... ,.. " ... ,...... , ........ ,..... ,.................... 3-6
Error Messages .................................... ................................... 3-7
xi

Operating Instructions ..........................................................
Initial Installation ................... ~..........................................
Turning Off the System ....................................................
Restarting the System ........................................................
Reloading the Functions ..................................................
Saving Programs on Paper Tape ....................................
Reloading Programs From Paper Tape ............................
CHAPTER 4

3-8
3-8
3-10
3-11
3-11
3-11
3-12

EDUSYSTEM 15

Introduction ...................... .................................................
System Components ...................................................... ..
~

4-1
4-1

BASIC Language Capabilities ........................................... . 4-2
Entering Programs ......................................................... . 4-2
Using Random Numbers ............................................... . 4-2
Listing the Program ... ~ ................................................... . 4-3
Executing the Program ................................................... . 4-4
Privileged Control Commands ....................................... . 4-4
DEC tape System Storage Capability ................... ~ ........ .. 4-5
Advanced System Capabilities ........................................... .
Running Very Long Programs ....................................... .
U sing a Data File ........................................................... .
Character Variables and String Capability .................... ..

4-6
4-6
4-7
4-8

Prograln Editing ................................................................. .

4-11

Error -Messages ................................................................... .
Program Loading Errors ................................................. .
Coding Errors ................................................................. .
Program Logic Errors ................................................... .

4-12

Operating Instructions ...................................................... ..
Loading the System ...................................................... ..
Initialize the DECtape Unit ........................ '.............. ..
Initialize Computer Memory ..................................... .
System Building Dialog .................................................. ..
Diagnostic Messages During System Building ........... .
Turning off the System .................................................. ..
Restarting the System ..................................................... .
XJl

4-12
4-13
4-15
4-16
4-16
4-17
4-17
4-19

4-23
4-25
4-25

Saving Programs on Paper Tape ....................................
Reloading Programs from Paper Tape ............................

CHAPTER 5

4-25
4-26

EDUSYSTEM 20

Introduction
System Components ................................................. ~ .... ..
System Expansion. ,.......................................................... ~.

5-1
5-1

5-2

EduSy~tem

20 BASIC ......................................................... . 5-2
Abbreviated Commands .................................................. . 5-2
Multiple Statements per Line ........................................ .. 5-4
Immediate Mode ............................................................ .. 5-5
INPUT Statement .......................................................... .. 5-6
Comments ...........................
5-6
Subscripted Variables ............. ,..............................-......... . 5-7
IF THEN Statement ...................................................... .. 5-8
Truncation Function (FIX) ........................................... . 5-9
CHR$ Function ......... -... ;................................................ . 5-9
ON ·GOTO Statement ............................. ~ ........................ .. 5-10
ON GOSUB Statement ................................................... . 5-10
RANDOMIZE Statement ............. ~ ................................ .. 5-11
8 ••••••••••••••••••••••••••••••••••••••••••••

Error

Mess~ges

................................................................... .

5-12

Program Editing .................... "............................................ .

5-14

Operating Instructions ....................................................... .
Loading EduSystem 20 BASIC ...................................... ..
Initial Dialog ................................................................... .
System Reconfiguration ................................................ ..
System Shutdown ............................ :.............................. .
System Restart ............................................................... ..
Program Storing Procedures ........................................... .
Teletype Paper Tape Punch ....................................... .
High-Speed Punch .................................................... ..
Program Reloading Procedures .......................... ~ ......... ..
Teletype Paper Tape Reader .................................... ..
High-Speed Reader .................................................. ..

5-16
5-16
5-17
5-21
5-21

xiii

5-21
5-21
5-22
5-22
5,-22
5-22
5-22

CHAFfER 6

EDUSYSTEM 25

Introduction ...... " .................... , ........................................... 6-1
System Components ... ,................................................... . 6-1
System Expansion ................ :.................. " ...................... . 6-2
BASIC Language Capabilities ........................................... . 6-2
Abbreviated Commands ................................................. . 6-2
Multiple Statements per Line ......................................... . 6-2
Immediate Mode ............................................................. . 6-3
INPUT Statement ..................
6-4
Comments ..
6-4
IF THEN Statement ...................................................... .. 6-5
ON GOTO Statement ................................................... . 6-6
ON GOSUB· Statement ................................................... . 6-6
RANDOMIZE Statement ............................................... . 6-7
Truncation Function (FIX) .......................................... .. 6-8
II •• II ••• , ••• , •• I'"

1> • • • • • • • • • • • ,

••••••••••••••••••••• ,

I I • • • I I • • I I • • • I I • • IIJ"

•••••••••••••••••••••••••••••••••••

Extended System Capabilities ............................................ ..
String Variables ............................................ ,.... ,........... .
Reading String Data ................. ,................................. .
Printing Strings ........................ " ....... ,................. ,....... .
Inputting· Strings ......................................................... .
Line Input .................................................................... .
Working with Strings ................................................. .
String Functions .......................................................... .
. CHR$ Function .................................................... ..
MID Function ...............................
LEN Function ................. , ..... ,...............................
CAT Function ................
Program Storage/Retrieval ............................................. .
Storing User Programs ............................................... .
Retrieving User Programs ......................................... .
Running Very Long Programs .................................. ..
Deleting Stored Programs ........................................... .
Using Public Library Programs ................................ ..
Data File Storage/Retrieval ........................................... .
Creating Data Files ..................................................... .
Reading Data Files .................................................... ..
1 •• I •••••••••••••••••••••

I ' ' ' • • • I I • • • I ' • • • • I I I I • • • • • • • • • • • • I_I • • • • •

XIV

6-8
6-8
6-8
6-9
6-9
6-10
6-11
6-11
6-11
6-12
6-1l
6-13
6~13

6-14
6-14

6-15
6-16
6-17

6-18
6-18
6-20

Listing Data Files ........................................................
Erasing Data Files ......................................................
Using Public Data Files ................. :............................

6-21
6-22
6-22

Error Messages ......................... :............................................

6-26

Program Editing' ..................................................................

6-28

Operating Instructions ........................................................
Loading EduSystem 25 ....................................................
Initialize the DECtape Unit ........................................
Initialize Computer Memory ......................................
Answer System Dialog ................................................
Establish Terminal Extensions ....................................
Cr~ate Data File Tape ................................................
Maintaining the Public Library ................................. ~....
Protecting DECtape. Files......... .................. .....................
Storing Programs on Paper Tape ....................................
Reloading Programs from Paper Tape' .................. "'........
System Reconfiguration ..................................................
System ·Shutdown ................ :............................................
System Restart ................................................................

6-31
6-31
6-31
6-31
6-32
6-35
6-37
6-38
6-39
6-39
6-39
6 . .40
6-40
6-40·

CHAPTER 7

EDUSYSTEM 30

Introduction . ..... ........ .... ........ ..... ........ ..... ....... ... ........ ...... ..... 7-1
System Components ......................................................... 7-1
System Expansion ... ~......................................................... 7-2
BASIC Language Capabilities ............................. ~..............
Using Random Numbers ............................... ;... ~............
Running Long Programs ................................................
Using a Data File ................................ .............................
Character Variables and String Capability ......................

7-2
7-5
7-5
7-6
7-8

Using the Interactive Terminal............................................
Entering a Program ........................................................
Using Multiple Statements per Line ....... ~........................
Listing the Program ........................................................
Executing the Program ............ ;......................................
Loading a Card ·Program for Interactive Use ................

7-11
7-11
7-12
7-12
7-13
7-13

Storing Program~ on Paper Tape ................................ ..
Reloading Programs from Paper Tape ...................... :... ..
Privileged Coritrol Commands ............................... :....... .
Using th~ System Storage Capability ............................. .
SAVE and UNSAVE Commands ............................. .
CATALOG Command ............................................. .
LENGTH Command ................................................. .
OLD Command ......................................................... .
Returning to Batch Mode ............................................... .
Program Editing .......................................................... ","
Writing and Running Card Programs .................................. .

Writing a Program on Cards ........................................ ..
Line Numbers .............................................................. .
BASIC Statements ............ :... :..................................... .
Statement Operand .................................................. ..
Summary of Card Marking Procedure ...................... ..
Submitting a Program to be Run ................................... .
The NEW Card ......................................................... .
The LIST Card ......................................................... .
The RUN Card ........................................................ ..
Summary ..................................................................... .
Getting the Results of a Computer Run ........................ ..
Using a Stored Program ................................................. .
Interacting with the Operator ....................................... .
Editing and Rerunning a Program ................................ ..
Inserting Messages in the Program Printout .................. ..
Sample Program ........................................................... .
Problem .................................................................... ..
Procedures ................................................................. .
Printed Results ........................................................... .
Executing Card Programs ................................................ ..

Normal Batch Operation .................................... :.......... .
Executing Card Programs Individually ......................... .
Controlling a Batch Run ................................................. .
BATC!I Command ................................................... .
MAX Command ........................................................ ..
fIEADER COlnmand ................................................. ..
STACK Command ..................................................... .
LOG Command ........................................................ ..
xvi

7-14
7-14
7~14

7-15
7-15
7-16
7-16
7-17
7-17
7-17
7-18
7-18
7-19
7-20
....
7-20
7-22
7-23
7-23
7-24
7-24
7-24
7-25
7-26
7-27
7-27
7-28
7-28
7-28
7-28
7-29
7-29
7-29
7-30
7-31
7-31
7-31
7-32
7-:32
7-33

Hands-On Interaction Versus Batch ................................. ~ 7-33
Enors Messages .. "...... ~
Batch Mode Program LoadiNg Errors ........................... .
Interactive Mode Program Loading Errors ................... .
Coding Errors """"""""""" ~"".""""""""""""""""""""""""""""" .. """"."""."""."""".
Program Logic Errors .... ;; ............................................. .
II • •

••••••••••••••••• '

••••••••••••••••••••••• ••••••••••

7-34
7-34
7-35
7-36
7-37

7-38
Loading EduSystem 30 ................................................ .. 7-38
Initialize the DECdisk ................................................. . 7-38
Initialize the DECtape Unit ...................................... .. 7-38
Initialize Computer Memory ....................................... . 7-39
System Building . Dialog ................... :............ .-................ . 7-39
Diagnostic Messages During System Build ................. . 7-43
Turning Off the System ........................ :........................ . 7-47
Turning On the System ................................................. . 7-48
Restarting EduSystem 30 ..................... ~ ........................ . 7-48
DF32 or RF08 Disk ................................................. . 7-48
TC01 DECtape ......................................................... . 7-49
TD8E DECtape ....................................................... ~ .. 7-49
Using Optional Hardware ............................................. . 7-50
LP08 Line Printer ................................................. ;.. .. 7-50
High-Speed Paper Tape Reader/Punch ..................... . 7-50
Punched Card Input .................................................. .. . 7-51

Operating Instructions ....-................................................... .

Calculating Available Storage

CHAPTER 8

7-52
EDUSYSTEM 40

Introduction

System Components ....................................................... .
System Expansion ......................................................... .
BASIC Language Capabilities ........................................... .

Advantages and Applications ...................................... ..
EduSystem 20 """"""",,"""""""""""""""
EduSystem 30 ........................................................... .
t·." ••• ,,"" ••• """"" •••• ,,"",, •• ,,""""" ••••

Language Summaries .................................. ~ .................... .

BASIC Statements and Commands ............................... .
xvii

8-1
8-1
8-2
8..2
8-2
8-2
8-3

8-4
8-4

Batch Control Cards ......................................................
BASIC Functions and Arithmetic Operations ................

8-8
8-9

Error Message Summaries ..................................................
EduSystem 20 ................................................................
EduSystem 30 ................................................................
Batch Mode Program Loading Errors ................ ,.......
Interactive Mode Program Loading Errors ................
Coding Errors ............................................................
Program Logic Errors ................................................

8-10
8-10
8-12
8-12
8-12
8-13
8-15

Loading and Operating Instructions ....................................
Initializing the DECdisk ................................................
Building EduSystem 40 on Disk ....................................
Starting EduSystem 40 ....................................................

8-16
8-16
8-16
8-20

CHAPTER 9

EDUSYSTEM 50

Introduction ........................................................................
User Programs ................................................................
User Files ................................................ ........................
System Configuration .......................................................
System Expansion ..........................................................'

9-1
9-2
9-2
9-3
9-4

EduSystem 50 Monitor ......................................................
Calling the Monitor ............. ~ .... ~ .....................................
Logging into EduSystem 50 ..........................................
Logging out of EduSystem 50 ........................................
System Library Program Control ....................................
Communication with Other Users ..................................
System Status Reports ....................................................
Resource Sharing ......................................... ;..................
Error Messages ................................................................

9-4
9-4
9-6
9-8
9-10
9-11
9-12
9-12
9-16

System Library Programs ....................................................
General File Characteristics ............ ..............................
Controlling the Execution of System Library Programs .: ..
Returning to the Monitor ......................................... ;......

9-17
9-18
9-20
9-21

XVlll

BASIC ... _............................................................................. 9-23

Truncation Function, FIX(X) ........................................ 9-24
ON· GOTO Statement....................................................... 9-24
SLEEP Statement ..... ;...................................................... 9-24
Comments ... ".......................-.............................................. 9-25

Blank Lines ................................................................... :.
Multiple Statements per Line ..........................................
Editing BASIC Statements ....... ;.............. ~ .......................
Saving Compiled Programs ..............................................
File Protection ..... :.: ........................................................
Project~Program~er Numbers ................................ :.......
Restricted Accounts ....................... ,................................
Catalog ForriI~t ....................................... :........................
Strings in BASIC ....................,.........................................
Reading String Data ~ ...................................................
Printing Strings ..............................................................
- Inputting Strings ..........................................................
Line Input ...................................

c. ••••••• , • • • • • • • • • • • • • • • • • • • • • • • •

Working with Strings ....................................................
The CHANGE Statement............................................
The CHR$ Functi,on ....................................................
Program Chaining ...... ,.... ,. .................................................
Disk Data Files .................................................................

9-26
9-26
9-26
9-27
9-27
9-28
9-28
9-29
9-29
9-29
9-31
9-31
9-32

9-33
9-34
9-36
9-36

9-38

File Rec.ords ..................... "......................................... 9-38

Opening a Disk File ....................................................
Reading/Writing Disk Files ........................................
Closing/Deleting Disk Files ........................................
DECtape Data Files ........................................................
DECtape File Records ....... ;........................................
Opening a DECtape File ............................................
Reading/Writing DECtape Files ................................
Closing DECtape Files ................................................
Using DECtape Data Files with OS/8 FORTRAN ....
Line Printer Output ........................................................
Paper Tape Output ..........................................................
Internal Data Codes ........................................................

9-40
9-40
9-42
9-43
9-43
9-44
9-45
9-46
9-46
9-47
9.-47
9-48

Numeric Data .............................................................. 9-48

String Data ....... .......... ..... ......... ...... ....... ...... ............ .... 9-50
Error Messages ......................................................... ........ 9-50

xix

FOCAL ..............................................................................
Using FOCAL Commands ..............................................
FOCAL Overview ............................... ,...... ,.....................
Numbers ............................................. ,...... ,.....................
Variable Names ..............................................................
Arithmetic Operations ..... =..............................................
Priority of Arithmetic Operations ................................
Enclosures ..................................................................
Input/Output Commands .............. .......... ................ ........
TYPE Command ........................................................
ASK Command ...... ~ ........................................... ,•......
Text Output with ASK ............................................
Computational Command. ...............................................
SET Command .......................................... :..................
Control Commands ........................................................
GO or GOTO Command ................................................
IF Command................................................................
If with Less Than Three Line Numbers ..................
Arithmetic Comparison with IF Command ............
DO Command ..............................................................
Nested DO ..............................................................
RETURN Command ..................................................
QUIT Command .-.......................................................
FOR Command ..........................................................
FOR with a DO ......................................................
Nested FOR and DO ..............................................
Subscripted Variables ..................................................
COMMENT or CONTINUE Command ...... ;.............
Edit Commands ......... ,...... ,.............................................
WRITE or WRITE ALL Command ..........................
ERASE and ERASE ALL Commands ., ......................
MODIFY Command ....................................................
Library Commands ..... ,.....................................................
LIBRARY SAVE ........................................................
LIBRARY CALL ......................................................
LIBRARY DELETE ......................................... ,........
LIBRARY LIST ........................................................
Error Messages with Library Commands ....................
Estimating Program Length ..........................._.................
Debuggl'ng ............................. , ....................................... .
xx

9-61
9-61
9-62
9-63
9-63
9-64
9-64
9-65
9-66
9-66
9-67
9-68
9-68
9-68
9-68
9-68
9-69
9-69
9-70
9-71
9-71
9-72
9-72
9-72 '
9-73
9-73
9-74
9-74
9-75
9-75
9-76
9-76
9-78
9-78
9-78
9-79
9-79
9-79
9-80
9-81

Using the Error Diagnostics ........................................
Using the Trace Feature ............................. ~ ..............
FOCAL Functions .................... ;.....................................
Sine Function (FSIN) ................................................
Cosine Function (FCOS) ..........................................
Exponential Function (FEXP) ..... ~ ..............................
Logarithm Function (FLOG) ....................................
Arctangent Function (FATN) ............ ~ .......................
Square Root Function (FSQT) ..................................
Absolute Value Function (FABS) ..............................
Sign Part Function (FSGN) ........................................
Integer Part Function (FITR) ....................................
Random Number Function (FRAN) ........................
FOCAL Output Operations ................... ~ ........................
Control Characters ..........................................................
~
Reading FOCAL Paper Tapes ..................
o . . . . . . ._ . . .

...........

FORTRAN-D .. .......... .......... .............................. ................
Calling FORTRAN-D .................... ;...............................
Using FORTRAN-D ........................................................
Line Format .................................. ..................................
Statement Numbers .. ................................. .................
Statement Continuation Character . .............................
FORTRAN Statements ..................................................
Comment Statements ......... :................... ~....................
Character Set ..............................................................
Constants . ....................................................................
Integer Constants ....................................................
Real Constants ..........................................................
Fixed and Floating-Point Representation ................
Variables ....................................................................
Integer Variables .....................................................
Real Variables ......... ........... .....................................
Scalar Variables ......................................................
Array Variables ......................................................
DIMENSION Statement ............................................
FORTRAN Arithmetic ....................................................
Arithmetic Operators ..................................................
Use of Parentheses ..................................................
Arithmetic Expressions ..............................................
XXI

9-81
9-82
9-82
9-83
9-83
9-84
9-84
9-84
9-85
9-85
9-85
9-86
9-86
9-86
9-87
9-88
9-95
9-95
9-96
9-97
9-98
9-98
9-99
9-99
9-100
9-100
9-100
9-101
9-101
9-102
9-103
9-103
9-103
9-104
9-104
9-105
9-105
9-106
9-107

Arithmetic Statements ............................... ,................ 9-108
Multiple Replacement .......................... " ................ 9-109
Mode Conversion .................................................... 9-110
Functions ................................................... "............. .. 9-110
Program Control ........................................... ............... .. 9-111
END Statement .......................................................... 9-111
STOP Statement .......................................................... 9-111
PAUSE Statement ........................................................ 9-112
GO TO Statement ...................................................... 9-112
Example of Integer Summation .................................. 9-113
IF Statement ................................................................ 9-113
DO Loops ................................................................... 9-115
CONTINUE Statement............................................ 9-117
Computed GO TO ...................................................... 9-118
FORTRAN Input/Output .............................................. 9-118
Data Formats .............................................................. 9-119
ASCII Coded Data ................................................ 9-119
Binary Coded Data ................................................ 9-119
Input/Output Statements ............................................ 9-119
ACCEPT and TYPE Statements ............................ 9-120
READ and WRITE Statements .............................. 9-121
Variable Specification in I/O Statements .................... 9-121
FORMAT Statement .................................................. 9-123
The A Format Specification ........................................ 9-124
Input Formats .............................................................. 9-125
Integer Values-the I Format .................................. 9-125
Real Values-the E Format .................................... 9-126
Output Formats .......................................................... , 9-126
E and I Formats ...................................................... 9-126
Format Control Specifications .................................. 9-127
Hollerith Output ...................................................... 9-127
Imp!ementation Notes .................................................... 9-128
Double Subscripts ........................................................ 9-128
Substatement Feature .................................................. 9-129
Error Checking ............................................................ 9-130
FORTRAN-D Source Program Restrictions .............. 9-131
FORTRAN-D Compiler and Operating System
Core Map ................................................................ 9-131
FORTRAN-D Error Diagnostlcs .................................... 9-133
Compiler Compilation Diagnost!cs .............................. 9-133
xxii

Compiler Systems Diagnostics ..................................... 9-135
Operating System Diagnostics...................................... 9-136
~

.PAL-D Assembler ..............................................................
Introduction ................... .................................................
. EduSystem 50 PAL-D ....... :............................................
Example of a PAL-D Program ........................................

9-137
9-137
9-137
9-138

Utility Programs ............................. :....................................
Symbolic Editor ....................................... ........................
Loader .............................................................................
Octal Debugging Technique ............................................
Catalog (CAT) ................................................................
System Status (SYSTA T) ....................,............................

9-145
9-145
9-149
9-150
9-153
9-154

Programs for Paper Tape and DECtape Control ................
PIP (Peripheral Interchange Program) ............................
PIP Conventions ................................ ...........................
Paper Tape to Disk Transfers ......................................
Disk to Paper Tape Transfers ....................................
High-Speed Reader/Punch Assignments ....................
BIN Format File Transfers ................. :....... ~ ................
Moving Disk Files .......... :......................................... \...
Deleting Disk Files ................................................... ....
BASIC File Transfers ..................................................
SAVE Format File Transfers ............. .........................
COpy Program ................................................................
Using and Calling COpy .......................... ".................
Loading'Files from DECtape ......................................
Saving Disk Files on DECtape ....................................
Listing Directories ......................................................
Deleting Files ........................................................ ;.....
Deleting all Existing Files on a Device ......................
Example of COpy Usage ............................................
AdvaDletl Monitor Cootmands ............................................
Introduction ............................................................. .........
Control of User· Programs ..............................................
Defining Disk Files ..........................................................
Creating a Disk File ........................ :...........................
Opening and Closing a File ............... ;..........................
Extending, Reducing, and Renaming a Disk File ......

9-157
9-157
9-157
9-157
9-158
9-158
9-159
9-159
9'-160
9-160
9-160
9-161
9-161
9-162
9-163
9-163
9-164
9-164
9-165
9-167
9-167
9-168
9-169
9-170
9-170
9-171

xxiii

Protection Codes
Error Conditions ...................................................... ..
Saving and Restoring User Programs ............................ ..
Utility Commands ......................................... "............... ..

9-171
9-173
9-174
9-177

Writing Assembly Language Programs ............................. .
Introductioll ................................................................... .
Console I/O .................................................................. ..
Files and Disk I/O .......................... :............................. ..
Assignable Devices ............ ,............................................ .
Program Control ............ "................................................ .
Program and System Status ........................................... .
PDP-8 Compatibility ............................................... ,....... .

9-179
9-179
9-180
9-183
9-190
9-195
9-197
9-200

Storage Allocation ............................................................... .
Storage Map .................................................................. ..
File Directories ............................................................... .
Prqject-Programmer Numbers ................................... ,.. ..

9-205
9-205
9-205
9-206

••••••••••• ,

••••••••••••• ,

•••••••••••••••••••••••••••• II

APPENDICES

Appendix A

Read-In Mode Loader ................................

A-I

Appendix B

Character Codes .... ......................................

B-1

Appendix C

EduSystem 50 Monitor Command Summary

C-1

Appendix D

EduTest ........................................................

D-1

LIST OF TABLES

Table
Table
Table
Table
Table
Table
Table
Table
Table
Table

1-1
1-2
1-3~

2-1
3-1
4-1
5-1
5-2
5-3
6-1

BASIC Statements ...... ,............................... .
BASIC Edit and Control Commands ....... .
BASIC Functions and Arithmetic Operations
EduSystem 5 BASIC Statement· Summary
EduSystem 10 BASIC Statement Summary
EduSystem 15 BASIC Statement Summary
EduSystem 20 BASIC Statement Summary
EduSystem 20 BASIC Function Summary
EduSystem 20 Error Messages ................ ~.
EduSystem 25 BASIC Statement Summary
XXIV

1-134
1-139
1-144
2-11
3-5
4-26
5-2
5-3
5-12
6-23

:Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
'Table
Table
Table
Table
Table

6-2
6-3
7-1
8-1
8-2
8-3
8-4
8-5
8-6

8-7
8-8
8-9
8-10
9-1
9-2
9-3
9-4
9-5
9-6
9-7
9-8
9-9
9-10
9-11

Table 9-12
Table 9-13
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table

9-14
9-15
9-16
9-17
9-18
9-19
9-20
9-21
9-22
9-23
9-24

EduSystem 25 BASIC Function Summary 6-26
EduSystem 25 Error Messages ................. . 6-26
EduSystem 30 BASIC Statement Summary 7-2
Statements ................................................. . 8-4
Edit and Control Commands .................... .. 8-6
Batch Control Cards ................................... . 8-8
Functions ................................................... . 8-9
Arithmetic Operations ............................. . 8-10
EduSystem 20 Error Messages ................. . 8-10
Batch Mode Program Loading Errors ....... . 8-12
Interactive Mode Pro'gram Load:ng Errors 8-13
Coding Errors ........................................... . 8-14
Program Logic Errors ............................... . 8-15
LOGOUT Options ..................................... .. 9-10
Monitor Error Messages- .......................... .. 9-16
Internal Data Codes .................................. .. 9-49
BASIC Error Messages ............................ .. 9-50
Non-Fatal Error Messages ......................... . 9-55
EduSystem 50 BASIC Language Summary .. 9-56.
FOCAL Command Summary ................... . 9-89
FOCAL Functions ..................................... . 9-92
FOCAL Error Messages ........................... . 9-93
FORTRAN-D Statement Summary ........... . 9-132
FORTRAN-D Compiler C6mpil~tion
t'ICS .................................................
,
·
.
D lagnos
9-134
FORTRAN-D Compiler Systems
·
st'ICS ................................................ .. 9-135
D lagno
FORTRAN-D Operating System
t'ICS ................................................. . 9-136
·
D lagnos
EduSystem 50 Symbol List ...................... .. 9-139
P AL-D Error Diagnostics .................. ,......... . 9-142
Symbolic Editor Operations Summary ....... . 9-146
EDIT Command Summary ...................... .. 9-147
ODT Command Summary ........................ .. 9-151
PIP Option Summary ................................. . 9-161
COpy Option Summary .......................... .. 9-165
Monitor Program Control Commands ....... . 9-169
Monitor Utility Commands ...................... .. 9-178
EduSystem 50 Internal Character Set ...... .. 9-192
EduSystem 50 lOT Instruction Summary .. .. 9-202
xxv

Table A-I
Table D-l

RIM Loader Programs .............................. ..
EduTest Error Messages ............................

A-I
D-I0

LIST OF ILLUSTRATIONS
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure

4-1
7-1
7-2
7-3
7-4
7-5
7-6
7-7
7-8
8-1
8-2
9-1
9-2
9-3
9-4
9-5
9-6
A-I
A-2

"System Building Dialog ................................ 4-20
EduSystem 30 BASIC Card .......................... 7-18
Line Number Example ................................ 7-19
Statement. Example ...................................... 7-20
EduSystem 30 BASIC Template .................. T-21
Marking the Statement Operand .................... 7-22
Completed BASIC Cards ............................ 7-23
BASIC Program Deck .................................. 7-25
System Building Dialog ................................ 7-44
Building EduSystem 40 ................ .'............... 8-18
Starting EduSystem 40 .................................. 8-21
Number Representation ................................ 9-102
Program Flow ................................................ 9-112
Legal and Illegal Nesting Techniques ............ 9-116
Program Branching in DO 'Loops ................ 9-11 7
EduSystem 50 Storage Map ........................ 9-205
File Directories ............................................ 9-206
Loading the RIM Loader .............................. A-2
Checking the RIM Loader ............................ A-3

XXVI

1
teach yourself:

basic
INTRODUCTION

BASICl is a conversational computer language which enables a
human to carry on a "dialog" with a computer. We will "talk" to
the computer by using a Teletype2 like the one shown below. Your
-terminal may be an alphanumeric cathode ray tube (CRT)
DECterminal or a high-speed DECwriter. Operations with these
terminals are, in most cases, identical w.ith the Teletype, so we .,
will only discuss the Teletype here.

OFF
REL.

B. SP.
ON

STARTSTOPFREE~

OFF
LINE

LOCAL

BASIC (Beginner's All-purpose Symbolic Instruction Code) is a trademark -registered by the Trustees of Dartmouth College.
2 Teletype is a registered trademark of the Teletype Corporation.
1

1-1

Using the Teletype, we type messages to the computer, requesting it to carry out operations. The computer performs the required
operations and prints the results on the same Teletype. If we
make certain mistakes or if we ask the computer to do something
"it cannot do, it may print an error message. For example, if we type
DO THE HOMEwORK ON PAGE 257

(and press the RETURN key)
INHAT1

the computer may respond by printing a message such as
WHAT?
The actual response depends on the EduSystem that you are
usmg.
If you wish to use the computer, you must:
Learn what the computer can do and what the computer cannot do.
Learn a language, such as BASIC, so that you can instruct
the computer to do things within its capability.
Communcate with the computer by means of the Teletype.
We will begin by assuming that you know little or nothing about
computers and will try to lead you through the following four
levels of "know-how."
1. You know nothing about computers. If you wish to .use a
computer to help you solve a problem, you describe the
problem to Susan. Susan uses the computer and returns the
answer to you.
2. You can operate the computer (Teletype), using a program supplied by another person. The program, however,
is gibberish to you-incomprehensible!
3. You can read and understand programs written by others
but are unable to write original programs of your own.
4. Computerland is yours! You can invent your own original
problem-solving pro~edures, write them in the BASIC language, check them out on the computer, correct them ("debug" them) if necessary, and obtain the desired results.
This chapter is designed to help you learn the fundamentals of
BASIC. Many examples and exercises are included to aid you in
discovering the elements of the BASIC language.
1-2

Teletype Keybourd
BASIC programs must be written using the symbols that appear
~n the Teletype keyboard. A diagram of the Teletype keyboard
lS

shown below:

'*"

fT\ f7'\ f7\ ('$\ 17\ fa\ f-"\
fl\ f \
f.\ ~
VV'-V-.V\.:.J\'v\'ve\"v\'vVV\V
~ f \ f \ r:;;) ~ ~ ( ) f \ (;;;\ A
(@\ ~ {;;\
~\.::J~\':"'\'v\'yY\::..J\.:J\V\:...J~~

8oe~vG)eDOOCDeCD@ee

Q()'OOOCDCDOG(D 8
SPACE

No other symbols may be used. For example, the following
symbols are commonly used in mathematics, but may not appear
in a BASIC program because they are not on the keyboard.

On the keyboard diagram, locate the keys with the foHowing
symbols:
ABC 0 E F G H I J K L M N

Letters:

Digits:

1 234 567 B 9 0

Special:

P Q R STU V

wx y z

To type any of the above symbols, simply press the appropriate
key. For example, to type the letter S, press the key on which S
appears.

1-3

Here is another copy of the key~oard chart so you won't have
to turn the page back.

e>cbCDC)G)(D0660cbcb©

~(\(\~~~()(\(';;;\:-ff\e0
~ \.V \!..J \.!..) \V.\V v \V \.:J
\.V ~ ~

@ee

80GJGJG)evQO(D,e:
8 OOOG)O ~ Q)OC)Q) 8

Locate the SHIFT keys. There are two of them, located at the
left and right ends of the bottom row of keys. When we refer to a
character that is typed while the SHIFT key is held down, we will
show it as SHIFT/Character. For e~ample, if we want you to type
a ~ (back arrow) we will tell you to type SHIFT/O.
We have drawn arrows to call your attention to the keys with
tlte following special characters.

()

* ....

To type any of these characters, you must hold either SHIFT
key down and press the key that has the desired character.

The space bar looks like this:

SPACE

Use it to insert spaces as you type.
(;;\
~

Locate the RETURN key:

Now you are ready to start "talking" to the computer.
1-4

GETTING ACQUAINTED WITH BASIC
Imagine that we are seated at the teletype and that (perhaps
with some help) we have attracted the attention of the computer.
We will begin with some absurdly simple programs.

If you try these programs; remember to press the
RETURN key at the end of each line that you type. If

you make a mistake, the compu~er may print'an error
message. Ignore it-retype the line.

Here we go!

SCR

10 PRINT 7
99 END

RUN
7

First, we type SCR and' press the
RETURN key. The computer
SCRatches (erases) any old program in its memory.
Then we enter our BASIC program,
consisting of two statements. Each
statement is on' a separate line. The
program is in the computer's memory.
We tell the computer to RUN the
program. It does and 'prints the re-

sult, 7.
The BASIC program is shown again below.

10 PHtNT' 7
99 END

It consists of two statements, a PRINT statement and an END

statement. Each statement begins with a line number. Read onit gets better. '
1-5

Let's do something a little more exciting.
SCR

First, we SCRatch the preceding
program.

1~ PRINT 3+4
99 END

And then enter a new program.
This program also has two statements.

RUN

We tell the computer to RUN the
program.

It does, The result is 7 since 3

4= 7.
20
30
40
40

PRINT
PRINt'
PRIIf!
PRINT

3-4
3*4
3/4
3/4

Then we type LIST and press the'
RETURN key.

LIST

10 PRINT
PRINT
PRINT
PRIN_T
END

20
30
40
99

Let's add three more statements.
We use 20, 30 and 40 as line numbers.

3+4
3-4
3*4
3/4

The computer LISTs the program
in its memory. Note that there are
five statements and that they are
listed in line number order.
O.K., let's RUN the program.

RUN

Here are the four results, one for
each of the first four statements in
the program.

-1
12

Exercise 1. Examine the preceding program, then write the symbol that is used to tell the computer to perform each of the following arithmetic operations. OPERATION

SYMBOL

Addition
Subtraction
Multiplication
Division
1-6

Remember these things.
WE TYPE

TO TELL THE COMPUTER TO

SCR

SCRatch (erase) the program in memory.

RUN

RUN the program in memory.

LIST

LIST the program in memory.

The statement
10 PRINT 3+4

tells the computer to evaluate the numerical expression 3
print the result. In this case, the result is 7.

+ 4 and

The statement

tells the computer to evaluate the numerical expression 3*4 (3
times 4) and print the result. This time, the result is 12.
The statement
99 END

simply marks the end of the program. Every BASIC program
musj have an END statement.
Each statement begins with a line number.' A line number may
be any counting number in the range:
1 ~ line number :::;;; 2046 .
Larger EduSystems permit line numbers to 9999, but 2046 is
plenty for most programs.
Instead of numbering statements with consecutive counting numbers (1, 2, 3, etc.) we use 10, 20, 30 and so on. This' gives us
room to insert a new statement between two old statements. For
example, if we had already entered a program using 10, 20, 30,
40 and 99 as line numbers, we could insert a sta,tement between
statement 20 and statement 30 by using 25 as the line number
of the new statement.
1-7

Exercise 2. Do not use the computer to do this exercise. Instead,
pretend that you are the computer. We have entered the following
program into your memory and told you to RUN the program.
Do it.

10
20
30
40
99

PRINT
PRINT
PRINT
PRINT
END

12+3
12-3
12*3
12/3

RUN

We entered this program, consisting
of five statements, into your memory.
O.K., computer, RUN the program ..
Indicate your answer by filling in
the blanks.

Exercise 3. You are·still the compuer. We will add a statement
to the program we entered in the preceding exercise.

50 PRINT 2*3+4

We add this statement.

LIST

LIST the program in your memory.

'-.

RUN-

Now RUN the program.

1-8

Numerical Expressions
The computer prints the value of a numerical expression as a
decimal numeral. The following table shows examples of computerprinted values of numerical expressions.
'

EXPRESSION VALUE

REMARKS

3.14
-123

A decimal numeral is a
decimal numeral

2+3+4
5-3+4
2*3*4
2*3/4

6
24
1.5

2+3+4=5+4=9
5-3+4=2+4=6
2*3*4....:... 6*4 = 24
2*3/4 = 6/4 = 1.5

2*3 +4
2 + 3*4
35 - 2*3
112+3
2 + 3/4
24/2*3

10
14
29
3.5
2.75
36

2*3 + 4 = 6 + 4 10
2 + 3*4 = 2 + 12 14
35 - 2*3 35 - 6 = 29
1/2 + 3 = .5 + 3 3.5
2 + 3/4= 2 + .75 2.75
24/2*3 = 12*3 = 36

11(2+3)
(2+3)/4
24/(2*3)

.2
1.25
4

1/3
2/3
100/3
200/3

.3333333
.6666667
33.33333
66.66667

=
=
=
=
=
=

. 11 (2 + 3) = 115 .2
(2 + 3)/4 5/4 1.25
24/ (2*3) = 24/6 =4

Value rounded to seven
significant digits.

NOTES
1. The operations are done in left to right
"order.
2. All multiplications and/ordivisions are done
before any additions and/ or subtractions.
To evaluate 24/2 *3 the computer first divides 24 by 2, obtaining 12. Then it mUltiplies
12 by 3, obtaining 36.
3. We use parentheses to modify the order in
which operations are done.

1-9

NOTE 1.

NOTE 2.

NOTE 3.

Your turn-but let someone else use the computer while you
work the following exercises.
Exercise 4. You are the guest star on the television program
"Computer for a Day." To win the grand prize (7 microbucks)
you must evaluate each of the following numerical expressions. Go!
(1) 3*4+5 _ _ _ __

(2) 3 + 4*5 _ _ _ __

(3) 3/4 + 5 _ _ _ __

(4) 3 + 4/5 _ _ __

(5) 3*4/5 _ _ _ _ __

(6) 3/4*5 _ _ _ __

(7) 3*(4

+ 5)

_ _ __

(8) 3/(4*5) _ _ __

(9) 3/(4

+ 5)

_ _ __

(10) 3/4/5 _ _ _ __

Use your computer to check the answers. Did you win the prize?
If not you can still win by finding a computer that evaluates numerical expressions the same way you do. Good lu~k!
Exercise 5. Complete the following table showing BASIC expressions that correspond to given mathematical expressions.

MATHEMATICAL EXPRESSION
(1) 2

x 3 + 4 -:- 5

BASIC EXPRESSION
2*3

(2) 37(43 - 19)

+ 4/5

37*(43 - 19)

(3) 3.14X 5 X 5

(4)

2
3+4

(5) 73 - 25

+ 53

Back to the computer to check your answers.
1-10

The PRINT Statement
Previously, we used PRINT-statements of the following form: .

n
where

n = line number
e = numerical expression

For example:
10 PRINT 3+4

Imenumber~
PRINT----------~

numerical expression _ _ _.....;.t
A PRINT statement of this· form directs the computer to computethe value (simplest form) of the numerical expression e and
to print the result on the Teletype.
The following program illustrates a PRINT statement that has
more than one numerical expression.

SCR

As usual, we first SCRatch any leftover program.

10 PRINT 3+4" 3-4" 3*4~ 3/4
99 END

Next, we enter the program. The
PRINT statement includes. four expressions.

RUN

Let's RUN the program.

-1

.75

Since the PRINT statement has four expressions, the computer
prints four results.
1-11

A more general form of the PRINT statement is shown below.
n

PRINT - list of expressions

For example,

10 PRINT 3+4" 3··4" 3*4" 3/4

line number

-.J

PRINT----....
list of expressions

--------001

Remember these things:
• A PRINT statement can contain more than one expression.
• One result is printed for each expression in a PRINT statement.
• If a PRINT statement contains more than one expression,
then the expressions must be separated by commas.

• Up to five (5) results per line are printed. If there are more
than five expressions in -the PRINT statement, additional
results are automatically printed on the next line;
For example, the statement

will cause the computer to print the following results.
RUN
1

2.4

1-12

.15

Exercise 6. Do not use the computer for this exercise. Instead,
pretend that you are the computer and RUN each of the following programs.
10 PRINT 1,2,3,4,5,6,1,8,9,10,11, 12
99 END

RUN

10 PRINT 1*2,2*3,3*4,4*5,5*6,6*1,1*8,8*9
99 END
RUN

Exercise 7. Each new PRINT statement causes a new line to
be printed. RUN this program.

10
20
30
40
50
60
10
99

PRINT
PRINT
PRINT
PRINT
PRINT
PRINT
PRINT
END

1,1*1
2,2*2
3,3*3
4,4*4
5,5*5
6,6*6
1,1*1

Once again ...
Each new PRINT statement
printed.
causes a new line to

RUN

1-13

If we use a semicolon (;) instead of a comma to separate expressions, the results will be packed mor,e closely together. For
example, try this one on your computer.
SCR

Goodbye, old program!

10 PRINT 3+4;3-4;3*4;3/4

Note the

s(~micolons

(;).

99 END

Watch the spacing in the results be-

low.
The results are "packed" more
closely together than if we had
used commas.

RUN
7 -1

.75

When we use semicolons to separate expressions, the computer
will print up to 17 results per line. The actual number, however,
depends on the number of digits that it must print. For example,
10 PRINT 1;2;3;4;S;6;7an9;

H~ill;

12;1:3; 14: 15; 16; 17; lR.:19

99 END

RUN
1
18

The first 17 results were printed on
the first line - the 18th result on
the second line.

Let's see what happens as the numbers get larger.

10 PRINT 1112;123;1234'12345;123456;1234567
99 END

RUN
1 12

123

1234

12345

1234056

1.234567E+06

This is a floating point numeral. We describe floating point numerals in the next section.
1-14

Remember these things:
• If a PRINT expression, contains more than one expression,

then the expressions must be separated by commas (,) or
semicolons (;).
• If commas are used for spacing, up to five results per line
are printed. If semicolons are used, the results are ':packed"

more closely together. The actual spacing depends on the
size of the numbers involved.
• If you want to find out more about spacing -

experiment!

EXPERlMEN~
Floating Point Numerals
Floating point notation is similar to scientific notation. The computer does it this way.

10
20
30
40
50
60
70

PRINT
PRINT
PRINT
PRINT
PRINT
PRINT
PRINT

10
100
1000
10000
100000
1000000
10000000

In the program each number is expressed in "standard" or "common"
notation.

99 END

RUN
10
100
1000
10000
100000
1.000000E+06
1.000000E+07

The numerals are printed' in standard notation, exactly as they are
written in the PRINT statements.

But these are printed as {loating
point numerals.

1-15

The following examples show the same number expressed in
"standard" notation, scientific notation and floating point notation.
If a number is larger than 6 digits, its numeral will be printed in
floating point notation.
STANDARD
NOTATION

SCIENTIFIC
NOTATION

1000000·
10000000
100000000
1000000000000

1X
1X
1X
1X

FLOATING
POINT
1.000000E + 06
1.000000E + 07
1.000000E + 08
1.000000E + 12

106
107
lOS
1012

Let's see how BASIC handles small numbers.

10 PRINT .1
20 PRINT .001
30 PRINT .000000001
99 END
RUN
.1

If a number has more than 2 decimal places, its numeral is printed
in floating point notation.

1.000000E-03
1.000000E-09

•

Exercise 8. Complete the following table showing the numerals
in scientific notation and standard notation corresponding to numerals given in floating point notation as they might be printed
by the computer.
FLOATING
POINT
1.00000E + 09

SCIENTIFIC
NOTATION
1 X 109
1 X 10-9

STANDARD
NOTATION
1000000000
.000000001

1.00000E - 09
2.00000E + 09
2.00000E - 08

2 X 109
2 X 10-8

3.00000E + 12
6.02000E + 23

6.02 X 1023

2000000000

.000000000000000123456

1.23456E - 16

1-16

Printing Messages
The PRINT statement in the following program directs the computer to print a message.

The "message is enclosed in quotation marks.
10 PRINT "I LIKE PEOPLE"
99 END
RUN
Let's RUN

the program.

The computer types the message.

I L IKE PEOPLE

Here is another example.

10 PRINT ttGOOD MORNING"
99 END
RUN
GOOD MORN ING

Unfortunately, if you RUN this program in the afternoon, the
computer will still print

GOOD MORNING

The next example illustrates the difference between a numerical
expression and the value of a numerical expression.

10 PRINT "3+4-",3+4
END

RUN
3+4=

This program directs the computer
to print the message "3 + 4 ="
followed by the value of 3 + 4.

READY.

1-17

If you didn't like the spacing in the printed results, you can use
a semicolon instead of a comma to control the spacing.

10 PRINT "3+4:";3+4
99 END
RUN

Semicolon spacing.

3+4:7

Exercise 9. You be the computer. RUN the following program
without using the computer-you do the work and fill in the
blanks.

10 PRINT "IF I WERE. A COMPUTER,,"
20 PRINT "1·'0 DO ARITHMETIC LIKE THIS"

30
40
50
60
99

PRINT
PRINT
PRINT
PRINT
END

"3+4.";3+4
"3-4-"J3-4
"3*4-"J3*4
"3/4-";3/4

RUN
IF I WERE A COMPUTER"
I'D DO ARITHMETIC LIKE THIS

Your work is here.

REMEMBER THIS: Anything enclosed in quotation marks in
a PRINT statement is printed exactly as
it appears. No arithmetic is performed.
1-18

Exponents-Computing a Power of a Number
The following program illustrates a new idea power of a number.
10 PRINT "5*5-5.2-"J5'2
20 PRINT "2*2*2-2. 3-" ;2"3
30 PRINT ~3*3*3-3'4·"J3'4

computing a

99 END

The t is on the bottom row of keys.
Hold the SHIFT down when you
wish to type t.

RUN
5*5-5 '2- 25
2*2*2-2'3- 8
3*3*3-3'4- 81

We' use the t key when we want to.
tell the computer to compute a
power of a number.

In math, we write 2 3 , but in BASIC we write 2 t 3. Remember·
-BASIC notation is not math notation even though there are
similarities.
Here are some examples showing the values of expressions in
which the t is used.
EXPRESSION

VALUE

2t5
3t2 + 4t2
(2 + 3)t4

32
25
625

REMARKS

2t5
2*2*2*2*2 32
3t2 + 4t2 = 9 + 16 25
(2 + 3)t4 = 5t4 = 5*5*5*5 = 625

Exercise 10. Write the value of each expression.

EXPRESSIO~

VALUE

YOUR REMARKS

It3
7t2
3t3
4t5

Unless parentheses are used to change the order, the computer
does powers first, then multiplications and divisions, then additions
and subtractions. (See Note 2, page 1-9.)
1-19

GATHERING SPEED
Variables
In mathematics, we have great freedom in selecting symbols to
use as variables. We use the letters A - Z of our alphabet, the
letters of the Greek alphabet and, in fact, any symbol that we may
"invent" for this purpose. In BASIC, however, we must restrict
you in your choice of symbols. For now, we impose this rule:
A BASIC variable may be any letter of the
alphabet. That is, any of the following may be
used as a variable:

ABCDEFGHIJKLM
NOPQRSTUVWXYZ
In BASIC, each variable refers to a distinct location in the computer's memory. It may help you to think of the computer's memory as a set of 26 boxes, labeled A through Z, like this:
A

-D

We call these boxes locations. Each location can hold one number at anyone time. This number is the value of the variable
corresponding to the location.
Exercise 11. LET A = 3. In other words, take pencil in hand and
write the numeral "3" in the box labeled "A." Then do the following in similar fashion:
(1) LET B

(2) LET P = 3.14

1-20

(3) LET Z =-1

The following example shows how we assign a value to a variable
in a BASIC program.

Assign the value 3 to the variable
A. Print the value of A.

10 LET A-a
20 PRINT A
99 END
RUN

And here it is (the value of A, that
is) .

A more general form of the LET statement is shown below.
n

where

LET

n = line number
v = BASIC variable
e = numerical expression
"

For example,

Here is some additional evidence .. You may wish to RUN the
following program.
Don't forget to SCRatch!

SCR
10 LET Aa.3·
20 LET' B-4
30 LET C-3+4
40 LET D-3-4
50 LET E-3*4
60 LET.F-3/4
7,0 LET 6-3'4
80 PRINT AJBICJDJEJFJG

(Note.the semicolons.)

:~~/l'\
3 4 7-1 12 .75 81
1-21

Let's see what happens-blow by blow-.as the computer RUNs
the program. Below is a trace of the program from the preceding
page. The trace shows the value of each variable after the statement on the same line has been carried out by the computer.

STATEMENT

10 LET A = 3

20 LET B = 4

40 LET D = 3 - 4

-·1

50 LET E = 3*4

60 LET F =3/4

-·1
_. 1

.75

70 LET G = 3 t4

-·1

.75

80 PRINT A'B'C'D'E'P'G
, .' , , , ,

-·1

.75

99 END

-1

.75

30 LET C = 3

The trace is an important idea-from now on, we will depend
on it. Therefore, you had better learn how to (1) read a trace and
(2) do a trace.

Exercise 12. Trace the following program .
STATEMENT

10 LET P = 5
20 LET Q = -123
30 LET R
40 LET S

= 57.3
= 2 *3 +

4* 5

50 PRINT P, Q, R, S
99 END

1-22

The LET statement directs the computer to compute the value
of the expression to the right of the "=" symbol and assign this
value to the variable that appears to the left of the "=" symbol.
This value replaces any previous value of the variable. For example,
REMARKS

STATEMENT

10 LET A = 1

Assign the value 1 to A.

15 PRINT A

Print the current value of A.

20 LET A = 2

Assign the value 2 to A.

25 PRINT A

Print the current value of A.

30 LET A = 3

Assign the value 3 to A.

35 PRINT A

Print the current value of A.

99 END

If we RUN the program above, we obtain the following results.
RUN
1

2
3

Exercise 13. Without using the computer, RUN each of the following programs. (Fill in the blanks.)
10 LET X-3
20 LET X-S
30 LET X-7
40 PRINT X
99 END
RUN

10 LET X-3
20 LET Y.S
30 LET Z-7
40 PRINT X;Y;Z·
99 END
Rl,1N

P.S.
On EduSystems, you don't have to type the word LET in an expression. In other words,

10 A

is equivalent to

10 LETA = 1

To be consistent with Dartmouth BASIC, we'll use LET in this
manual but you don't have to on your EduSystem.
1-23

Variable Expressions
A variable expression is an expression that contains a variable.
For example, the following are variable expressions:

A-B

A/B

2*X

-c

P/Q

+ c/n

A*(B

+ C)

3.14*R t 2.

We evaluate a variable expression by assigning values to its variable or variables and carrying out-the indicated operations.

For example, A *B is a variable expression with variables A and
B. If A = 3 and B = 4, then the value of A*B is 12. But if
A = -7 and B = 5, then the value of A*B is --35.'

VARIABLE
EXPRESSION
A

VALUE(S) OF
VARIABLE(S)

=3
= -123
A = 12 and B = 7
A
A

A-B

X = 3.14
X =-6

2*X

P = 35 and Q 5
p= 2 and Q = 3

P/Q

C=8
C=O
c= -12

-C

A*(B

= 3 and B =

+ C)

3.14*R t 2

= 3, B = 4, C = 5
R=3

1-24

VALUE OF
EXPRESSION
3
-123

5
-1

6.28
-12
7
.666667-8
0

12
27
28.26

Each of the following programs directs the computer to evaluate
one or more variable expressions and print the result or results.
We use LET statements to assign values to variables.
10 LET A-3
20 LET a-4.
30 PRINT A*B

10 LET A-3
20 LET B-4
30 PRINT A+B
99 END

99: END

RUN

RUN
12

Exercise 14. Without using the computer, complete each RUN
by filling the blank with the result.
10 LET A-3
20 LET B-4
30 PRINT AlB

10 LET A-3
20 LET B-4
30 PRINT A-B
99 END

99 END

RUN

Exercise 15. The following program illustrates the use of variable
expressions. Trace the program by filling in the blanks under the
headings "A" through "G."
PROGRAM

10 LET A= 3
20LETB = 4
30 LETC=A + B
40LETD=A-B
50LETE= A*B
60 LET F = AlB·
70 LET G·= AtB
80 PRINT A;B;C;D;E;F;G
99 END

1-25

DEF

FEEDING THE BEAST
The INPUT Statement
In this section, we introduce a statement called the INPUT statement. But first, let's solve a problem that may point up the need
for the INPUT statement.
Problem. The area A of a circle of radius R is given by the
formula: .
where

7f'

= 3.14

We want to use the computer to compute the areas of three different circles. These circles have radii
R == 2, R == 3, and R ---:- 8.
Here is a step-by-step description of how we could use a computerto solve the problem.

seR

First, SCRatch any old program.

10 LET R-2
20 PRINT R,3.14*Rt2
99 END

Here is our program. It will work
for R = 2.

RUN

Let's RUN it.

For R

10 LET R-3

Do NOT type SCR. Instead, enter
a new Statement 10.

RUN
3

28.26

For R

= 2, the area is 12.56.

= 3~ A = 28.26.

10 LET R-8

Again-change Statement 10.

RUN

And RUN the program.

200.96

For R

1-26

= 8, A = 200.96.

We can reduce the amount of work required to solve the problem on the preceding page by using the INPUT statement. Here
is a program that uses an INPUT statement to permit input ofa
value of R.
10 INPUT,R
20 PRINT R,3.14*Rt2

We enter this program.
And tell the computer to RUN it.

99 END

The computer types a question
mark and stops.

RUN
1

For a second, we sit and contemplate that question mark. What
does the computer want? Of course! It wants a value for R. So
we enter 2 as the value of R and press the RETURN key. The
computer then prints

12.56

O.K., here is a RUN for R
on your computer.

= 2, R = 3 and R = 8. Try this one

SCR

SCRatch any previous' program.

1121 INPUT R
2121 PRINT R,3.14'*fif2

Enter the program.

99 END

RUN

RUN the program.

12
2

12.56

RUN
13
3

RUN, the program again.

28.26

RUN
18
8

Enter 2 and press RETURN.
For R :::: 2, A := 12.56.

Enter 3 and press RETURN.
For R = 3, A = 28.26~
RUN the program again.

21210.96

Enter 8 and press RETURN.
For R
8, A
200.96.

1-27

The general form of the INPUT statement is
line number

INPUT

list of variables

For example,
10 INPut A.. B,C

line number
INPUT
list of variables
Note that only the variables in the list are separated by com~as.
There is no comma following the word "INPUT" and there is no
comma after the last yariable in the list.
The INPUT statement directs the computer to type a question
mark and then stop and wait. Now you must understand that
computers are very patient-if you don't cooperate, the computer
will simply wait-and wait-and wait. To prevent this from happening, all you have to do is feed the computer-it's hungry-it
wants data.
Remember these things:
• The INPUT statement causes the computer to type a question mark.
• When the question mark appears, the pperator must enter
one value for each variable in the INPUT statement. The
values are entered in the same left to right order as the variables appear in the INPUT statement.
o

Don't forget to type commas between values.

After entering the last number, press the RETURN key. If
you have done everything correctly, the computer will proceed.

Here is another example.
17 INPUT A"B .. C
23 PRINT A*CB+C)
99 END

RUN
13,,4 .. 5
27

Since there are three variables, we
must enter three values.

If A
3, B
A*(B + C)

1-28

= 4, C = 5, then
= 27.

Exercise 16. There is something wrong with each INPUT statement shown below. For each one, circle the mistake and write the
reason.

I~CORRECT

STATEMENT

REASON

10 INPUT ,A,B,C,
20 INPUT X,Y,
30 IMPUT P,Q,R,S,T
40 INPUT A+B
50 INPUT I;J;K
60 INPUT AA,BB,
70 INPUT AB C

Exercise 17. We ran two simple programs. Here they are but
some things are missing. Complete each RUN by filling in the
blanks.

10 I NPUT A;B, C
20 PRI NT A
.)0

PRI NT B, C

12 INPUT U,V,W,X
25 PRINT U,U+V
36 PRINT W,W*X

99£ND

99 END

RUN
1-2,-3,-4

RUN
1_-

1-29

The GO TO Statement
The following program appeared on page 1-27.
10 INPUT R
20 PRINT RI3.14*Rt2
99 END

When we used it, we had to type RUN for each value of R. (See
page 1-27.) To eliminate the need to type RUN for each new
value of R, we add the following GO TO statement.
30 GO TO 10

(This directs the computer to "GO
TO Statement 10.")

Here is a RUN of the modified program. Try it on your computer.

seR

First, let's SCRatch.

10 1 NPUT R
20 PRINT R,3.14*Rt2
30 GO TO 10
99 END
RUN

Then enter the program.

12
2
13
3
18
8

12.56
28.26
200.96

Here is our GO TO statement.
Now let's RUN the program.
Each time after printing the results
the computer does a GO TO 10
and automatically restarts at the
INPUT statement.
How do we tell the computer we
are finished? Hold CTRL down,
press C, and release. The computer
will stop.

1-30

The GO TO statement has the general form
line number

GO TO

line number

The GO TO statement directs the com""
puter to GO TO the statement that has
this
30

For example:

GO TO

line number
GO TO
line number
Exercise 18. Do not use the computer to answer this. If you were
a computer and you came to the following statement, what would
you do?
.
115 GO TO 45

Exercise 19. Complete the following program to convert from
degrees Centigrade to degrees Fahrenheit.
In math notation, the formula is F
10 INPUT C

'C + 32

(You write the formula-in
BASIC.)

20 LET F-

30 PRINT C"F
40 PRINT
50 GO TO

(00 TO where?)

99 END
RUN

10
0

If C

= 0, then F = 32.

1100
100

212

If C

= 100, then F = 212.

137
37

(Hint: Body temperature)

Give F, what is C?

1-31

READ and DATA Statements
Whenever possible, we prefer providing data (values of variables) by means of the READ and DATA statements. The following program is a modification of our "Area of a Circle" friend on
page 1-26.

10 READ R
20 PRINT R,3.14*Rt2

This is a READ statement.

30 DATA 2,3,8

This is a DATA statement.

40 GO TO 10
99 END
RUN

Here are the results." On each line,
the value of R is on the left and
the value of the area is on the right.

12.56
28.26
200.96

3
8

DATA ERROR AT LINE 10

This message may be different or
even omitted. It simply means that
the computer has READ all the
DATA.

The statement

10 READ R

tells the computer to read one value of R from the list of values in
the DATA statement. Each time the READ statement is executed,
the computer reads the next value from the DATA statement. In
other word~, the computer remembers what values have already
been read.
.
If there is no more data to be read in the DATA statement, the

computer stops automatically.
1-32

Here is another example using the READ and DATA statements:
Four students' named Frodo, Sam, G and alf, and Strider have
each takep three quizzes. Their scores are:

..
STUDENT

FIRST SCORE SECOND SCORE THIRD SCORE

Frodo

Sam

Gandalf

Strider

We have written a. program to compute the. arithmetic mean
(average) of three scores and have run it for the above data.

10
20
30
40
90
91
92
93
99

READ XIY .. Z
LET M-(X+Y+Z)/3
PRINT X.. YIZ .. M
GO TO 10
DATA 66 .. 81 .. 75
DATA 91 .. 88 .. 95
DATA 78 .. 78 .. 62
DATA 80 .. 83 .. 86
END

We use X, Y, Z to denote the first,
second and third scores.
Frodo's scores.
Sam's scores.
Gandalf's scores.,
Strider's scores.

RUN
66
91
78
80

81
88
78
83

75
95
62
86

74
91.33333
72.66667

DATA ERROR AT LINE 10

, The averages of the three scores are in this column.

DATA statements may be' placed anywhere in the program.
They must, however, have line numbers smaller than the line number of the END statement.
1-33

The general form of the READ statement is

For example:

list of variables

READ

line number
10

READ

X, Y, Z

line number

The variables are
separated by
[ commas.

READ
list of variables

Exercise 20. There is probablyH something wrong with ~ach of
the following READ statements. For each one, circle the mistake
(if possible) and write the reason.

INCORRECT STATEMENT

REASON

10 READ, A,B,C
20 READX,Y
30 REED P,Q,R,S,T
40READA+B
50 READ I;J;K
60 READ AA,BB
70 READ ABC
80 READ 3.14

The READ statement directs the computer to read one value
from the DATA statement for each variable in the READ statement. If there are two or more DATA statements in a program,
the values in the statement with the smallest line number are used
first, then the data in the statement with the next smallest line
number and so on.
3

Depends on the system ... EXPERIMENT!

1-34

The general form of the DATA statement is:
line number
For example:
line number

,list of numerals

DATA
DATA

66, 81, 75 .

DATA··-- - _.....
list of numerals _ _ _ _..I

Expressions such as 2 + 3 are not allowed
in the list.

Exercise 21. There is something wrong with each of the following DATA statements. For each one, circle the mistake and write
the reason.

INCORRECT STATEMENT

REASON

10 DATE 1, 2, 3,4
20 DATA 112,2/3,3/4
30 DATA A, B, C, D, E
40 DATA, 3.7, 2.9
50 DATA 3.7,2.9,

The following three sets of DATA statements are equi\.:alent.
90 DATA 2,3,6,8, 12, 15, 19,27,33,26,47, 59
90 DATA 2,3,6
91 DATA 8,12,15; 19,27
92 DATA 33, 26, 47, 59
90 DATA 2, 3, 6, 8,12,15
91 DATA 19, 27, 33, 26,47, 59
That's right, the numerals in the list are separated by commas.
1-35

The RESTORE Statement
The RESTORE statement allows you to reuse DATA statements,
beginning with the lowest numbered DATA statement in the program. An example of the use of the RESTORE statement is shown
below:
10
20
30
40
50
60
70

DATA 2,,3,,6
DATA 8,,12,,15
READ A"B .. C.. D·
PRINT A"B"C"D
RESTORE
READ E"F
PRINT E"F
99 END

The RESTORE statement at line
50 allows the READ statement at
line 60 to obtain values 'from the
DATA statement at line 10

RUN
2
2

3
3

Without the RESTORE statement, an error message would have
occurred, indicating a lack of data for the READ statement at line
60.
'
Exercise 22. Without using -the computer, RUN each of the following programs. (Fill in the blanks.) If you wish, check your answers with the computer.
10 DATA 1,,2
20 READ A"B
30 PRINT A"B
40 RESTORE
50 DATA 3,,4
60 READ C.. D
70 PRINT C"D
99 END
RUN

10 READ X
20 PRINT X
30 RESTORE
40 READ Z
50 PRINT Z
60 DATA 4 .. 1.. 2
70 DATA 3 .. 5 .. 7
99 END
RUN

1-36

More Messages
We can make the results more readable by including' a statement
that causes the computer to print a heading. For example

Print a heading.

5 PRINT "RADIUS"~"AREA"
10 READR
15 DATA 2~3 .. 8,
20 PRINT R~3\14*Rt2
25 GO TO 10' c
99 EN·D
RUN
RADIUS
AREA
2
12.56
3
28.26.
8
200.96
DATA ERROR AT LINE.10

Exercise 23. Time to. play computer. Without using the com- .
puter, RUN the following program.

10 PRINT "L·'~ "R" ~ "L* 10+Rtf~ "L*8+R"
13 READ L~R
21 PRINT L~R.L.10+R~L*8+R·
27 GO TO 13
85 DATA 0~7"1.0~1.1.1.1.;'2,,.e .. 1,,7
99 END

Headings

RUN

Numerical results

1-37

Exercise 24. We have written a program to compute the
a triangle, given the base B and the height H as data.

AREA'"

~rea

t BH =BH/2

We want to complete the following table.

AREA

Here is our program. Complete it by filling in the DATA stat.ement. Then, if you can get on the computer, RUN it and cqmplete
the above table.

10 PRINT "B","H","AREA"
20 READ S,H
30 PRINT B~H,B.H/2
~"

GOTO 20

90 DATA
99 END

1-38

YOU CAN COUNT ON IT
~oops

Let's teach the computer to count. That is, let's develop a program to direct the computer to generate and print consecutive
counting numbers. The counting numbers are:
1, 2, 3,A, 5, 6, 7, 8, ...
Here is our program and a RUN as evidence that it does what
we claim.
Beware! If you RUN the following program,
you may have trouble stopping the computer.
Check with someone who knows how to interrupt your computer.

10 LET K:1
20 PRI NT K
30 LET K :K+l
40 GOTO 20

Assign the value 1 to K.
Print the current value of K.
Increase the vf\lue of K by 1.
Go around again.

99 END

RUN

Let's RUN the program.

2
3
4
5
6
7

If we don't interrupt the computer,

it will go on and on-printing
counting numbers. We· can interrupt the computer by holding the
CTRL key down and pressing C.

and so on.
The above program contains a loop. The loop is described below.
10 LET K-1
20 PRINT K

30 LET K-K+l
40 GO TO 20
99 END

This is a loop. The statements in
the loop are repeated indefinitely.
Each time through the loop, the
current .value of K is increased by
1 and the loop is repeated.

1-39

If you are confused by the statement

30LETK

BEFORE

=K + 1

STATEMENT

AFTER

30 LET K=K+ 1

Remember the general form of the LET statement.
line number

LET

variable

expreSSIOn

The expression may be any BASIC expression. The LET statement directs the computer to evaluate the expression and then assign the value to the variable. If the-expression is a' variable expression, it is evaluated using the current values of its variable or
variables.
Therefore, the statement LET K = K + 1 directs the computer
to evaluate the expression K + 1 using the current value of K and
then assign the new value to K.
Exercise 25. Show the value· of the variable after the statement
has been executed.

STATEMENT

BEFORE

AFTER

30 LET K·= 1

40 LET E=E+2

1-40

Loops Exposed
In order to clarify what happens as the computer executes the
program, we will "unwrap" the loop and trace it. The following
trace shows the value of K following the execution of each statement in the program. Under the heading "OUTPUT" we also show
results printed by the computer. We have traced the program seven
times through the loop.
Study this trace carefully. We will ask you to do several such
traces.

STATEMENT

10 LET K = 1

OUTPUT

REMARKS

20 PRINT K
1
30 LET K=K+ 1 2
40 GO TO 20
2

First time through the loop.

20 PRINT K
2
30 LET K=K+ 1 3
40 GO TO 20
3

Second time through the loop.

20 PRINT K
30 LET K = 1 +1
40 GO TO 20

3
4
4

Third time through the loop.

20 PRINT K
4
30 LET K=K+ 1 5
40 GO TO 20 .
5

Fourth time through the loop.

20 PRINT K
5
30 LET K=K+ 1 6
40 GO TO 20
6

Fifth time through the loop.

6
20 PRINT K
30 LET K=K+ 1 7
7
40 GO TO 20

Sixth time through the loop.

7
20 PRINT K
30 LET K ,= K + 1 8
40 GO TO 20
8

Seventh time through the loop.

and so on!

1-41

Exercise 26. Without using the computer, show the first five results printed by the computer under control of each of the following
programs. (Fill in the blanks.)
10 LET X-I
20 PRINT X

30 LET X-X+2
40 GO TO 20
99 END

10 LET E=2
20 PRINT E

30 LET E=E+2
40 GO TO 20
99 END
RUN

RUN

and so on.

Exercise 27. Complete each program (fill in the blanks) so that
when we run the program, the computer will produce the results
shown.

10 LET J20 PRINT J
30 LET J.

12 LET P-

25 PRINT P
33 LET p.

40 GO TO 20

41 GO TO

99 END

RUN

3
4

8
16

and so on.

and so on.
1-42

Exercise 28. This is a trace of one of the programs shown in
Exercise 26. Complete the trace for three times through the loop.

STATEMENT

10 LET X = 1 .

20 PRINT X
30 LET X=X+2
40 GO TO 20

1
3
3

OUTPUT

REMARKS

First time through loop.

20 PRINT X
30 LET X=X+2
40 GO TO 20

Second time.

20 PRINT X
30 LET X=X+2
40 GO TO 20

Third time.

20 PRINT X
and so on.

Fourth time and we quit!

Exercise 29. Here are two variations on previously written programs. For each one, show -the first four results.
1,0 LET K-0

20
30
40
99

LET K-K+l
'PRINT K
GO TO 20
END

RUN

and so on.

10
20
30
40
99

LET K-l
PRINT 2*K
LET K-K+l
GO TO 20
END

RUN

and so on

1-43

Exercise 30. Trace the following program four times through
the loop~
10 LET A-I
17 LET B-1

25
30
36
43

LET C-A+B
PRINT A
LET A-S
LET Bille

50 GO TO 25
99 END

STATEMENT

REMARKS

These statements are done once.

10 LET A= 1
17 LET B = 1
25
30
36
43
50

LET C=A+B
PRINT A
LET A=B
LET B =C
GO TO 25

First time through loop.

25
30
36
43
50

LET C=A+B
PRINT A
LET A=B
LET B = C
GO TO 25

Second time through loop.

25
30
36
43
50

LET C=A+B
PRINT A
LET A=B
LET B =C
GO TO 25

Third time through loop.

25
30
36
43
50

LET C=A+B
PRINT A
-LET A=B
LET B = C
GO TO 25

Fo~rth

1-44

time through loop.

FOR-NEXT Loops
The loops we have used so far do not terminate by themselves.
They go on, and on, and on .... until someone manually interrupts.
Now let's look at a loop that terminates automatically. This loop
makes use of two new statements caned the FOR statement and
NEXT statement.
10 FOR Ka1 TO 5

20 PRINT K
30 NEXT K

We call this a FOR-NEXT loop.

99 END

RUN

.Let's Run it and see what happens.

1
2
3

We did not interrupt.
The computer stopped
cally.

automati~

Perhaps the following trace will help you understand how a
.FOR-NEXT loop works.

STATEMENT

OUTPUT

REMARKS

10 FOR K = 1 TO 5

20 PRINT K
30 NEXT K

1
2

First time through loop.
K~ 5. Do it again.

20 PRINT K
30 NEXT K

2
3

Second time through loop.
K ~ 5. D it again.

20 PRINT K
30 NEXT K

3
4

Third time through loop.
K ~ 5. Do it again.

20 PRINT K
30 NEXT K

4
5

Fourth time through loop.
K ~ 5. Do it again.

20 PRINT K
30 NEXT K

5
6

Fifth time through loop.
K> 5. Stop the loop!

99 END

K starts at 1.

Everything stops.

1-45

A FOR-NEXT loop consists of three things.
1. A FOR statement
2. A NEXT statement
3. A set of statements between the FOR statement and the
NEXT statement.
A FOR-NEXT loop begins with a FOR statement and ends with
a NEXT statement. The set of statements between FOR and NEXT
is called the body of the loop. Here is a "pictorial" representation
for a FOR-NEXT loop.

10 FOR X _ l : 12
:J0

The same variable must be used
in both places.

body of the loop
50 NEXT X

Here is another example.

I
10
20
30
99

FOR N-2 TO 7
PRINT N
NEXT N
END

This FOR statement defines a set
of values for N. The set is:
[ 2, 3, 4, 5, 6, 7 ]

RUN
2 ...
3
4 _

5
6
7 ....- - - -......

The body of the loop is executed
repeatedly, once for each value of
N defined by the FOR statement.
Every FOR statement must have a
NEXT statement and every NEXT
statement must have a FOR statement.

Has it occurred to you that the value of tht;: variable increases by
one each time throu'gh,the loop?
1-46

Exercise 31. In each program, circle the body of the FORNEXT loop.
10 PRINT "RADIUS","AREA"
20 FOR R-2 TO 4
30 PRINT R,3.14*Rt2
40 NEXT R

10
20
25
30
40

99 END
RUN .

RADIUS
2
3
4

PRINT ,"RADIUS··,"AREA"
FOR R-2 TO 4
LET A-3.14*Rt2
PRINT R,A
NEXT R

99 END

AREA
12.56
28.26
50.24

RUN

RADIUS

AREA
12.56
28.26
50.24

3
4

Remember these things.
• The FOR statement defines a set of values for the variable.
• The body of the loop is executed for each member of the
set.
• The NEXT statement causes the body of the loop to be executed again, using the next member of the set. However, if
all members of the set have already been used, then the
NEXT statement directs the computer to move on to the
statement following the NEXT statement.
The following shows the set of values defined for the variable in
each example of a FOR statement. We have omitted line numbers.
FOR Statement

Variable

Set of Values for the Variable

FOR J = 0 TO 3

[ 0, 1, 2, 3 ]

FOR 1=1 TO 1

[ 1}

FOR A= 3 TO 5

[ 3, 4, 5 }

FOR X= -2 TO 2

[ -2, '-1,0, 1, 2 }

FOR B = 1 TO 0

Empty -

the loop is skipped.

Do you see a pattern? Try the following exercises.
1-47

Exercise 32. Complete the following table.

FOR Statement

Variable

FOR N == 1 TO 6

FOR C = 0 TO 5

Set of Values for the Variable

FOR W=-3 TO 0
FOR E= 12 T0.12
FOR T=7 TO 5

The next three are tricky. Be brave-guess!

FOR X =.5 TO 2.5
FOR Y = 1 TO 2.5

FOR Z=.5 TO 3

Exercise 33. Time to play computer. RUN each program as if
you were the computer.

10 fORX=2 TO 4.

20 PRI NT X,X*X
30 NEXT X·
99 END

RUN

12 fOR K:1 IO 3
23 LET P:2tK
30 PHI NI K,P
37 NEXT K

99 END

RUN

1-48

Instead O'f using the cO'mputer to' grind O'ut numbers, let's use it
to' print patterns.

10 FOR Kal TO 8
20 PRINT "**********"

10 FOR K-l TO 7
20 PRINT "XOXOXOXOX"

30 NEXT K
99 END

NEXT.K
END

30
99

RUN

**********
**********
**********
**********
**********
**********
**********
**********

xoxoxoxox

XOXOXOXOX
XOXOXOXOX

xoxoxoxox

XOXOXOXOX
XOXOXOXOX
XOXOXOXOX

10 PRINT "XXXXXXXXX"
20 FOR Kat TO 5

10 FOR K-I TO 3
20 PRINT "+-+-+-+-+-+-+"
30
40
99

30 PRINT "XOOOOOOOX"
40 NEXT K

PRINT "-+-+-+-+~+-+-"
NEXT K
END

50 PRI NT "XXXXXXXXX"
99 END

RUN
XXXXXXXXX
XOOOOOOOX

RUN
+-+-+-+-+-+-+
-+-+-+-+-+-++-+-+-+-+-+-+
-+-+-+-+-+-+_.
+-+-+-+-+-+-+
-+-+-+-+-+-+-

xooooooox
xooooooox
XOOOOOOOX
xooooooox
XXXXXXXXX

Exercise 34. Write a program to' generate each pattern .

. *******
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*******

+-+-+-+-+-+-+
-+-+-+-+-+-++-+-+-+-+-+-+
-+-+-+-+-+-++-+-+-+-+-+-+
-+-+-+-+-+-++-+-+-+-+-+-+
-+-+-+-+-+-++-+-+-+-+-+-+

1-49

The STEP Clause
A variation of the FOR statement is shown in the following program.
10 FOR K-I TO 9 STEP 2
20 PRINT K
30 NEX1' K

Note the STEP clause.

99 END

The STEP 2. clause causes the value
of K to increase by 2 each time.
You can verify this by examining
the printed results.

RUN
I
3
5
7
9

The following shows the set of values defined for the variable in
each FOR statement. We have omitted line numbers.

FOR Statement

Values of the Variable

FOR E = OTO 10 STEP 2

E= 0, 2,4,6, 8,10

= 0 TO 11 STEP 2

E= 0, 2,4,6, 8,10

FOR E

= 1, 1.5,2, 2.5, 3
W = 1,1,1, ...

FOR X = 1 TO 3 STEP.5

FOR W = 1 TO 7 STEP 0

Exercise 35. Complete the following table.
FOR Statement

Values of the Variable

FOR T = OTO 6 STEP 3

FOR N = 1 TO 5 STEP 1

N=,

FOR K

= 100 TO 130 STEP 10

FOR X

= OTO 1 STEP .25

K=
X=

Now--be careful on the next two!
FOR E = OTO 0 STEP 2

FOR B = 3 TO 0 STEP-l

1-50

In the following example, we use a space-saving trick.

12 t.B'R X-0 TO 12 STEP 2
23 PRINT X,
35 NEXT X
99 END
RUN

o
10

Aha! Note the comma.

Exercise 36. If the PRINT statement ends with a comma, results
are printed across the page, with up to five results per line. Here
is another example-we call it program COUNTDOWN.

10
20
30
40
50
60
70

FOR N=10 TO 1 STEP -1
PRINT N..
NEXT N
PR):NT "BLAST-OFF I I."
FOR K-l TO 55
PRINT ">"J
NEXT K

99 END

A semicolon to the rescue~.
,

RUN
10
5

9
4

8
3

7
2

6
1

BLAS]" -0 FF I I I
»»»»»»»»»»»»»»»»»»»»»»»»»>,»»

1-51

Be sure to RUN this program on your computer.
Variable FOR Statements
By using variables instead of numerals, we obtain variable FOR
statements such as the one in the following program.

10 INPUT N .....~7.::::====Seeit!

20 fOR K=ITO N .....
30 PRI NT K
40 NEXT K
50 GOTO 10
99 END

Variable FOR-NEXT loop.

N_-----------We =3 =
enter

RU ...

13......

1
2
3

-------------

3, K

1, 2, 3.

_ We enter 5 as the value of N.

15.-4
1

For N

as the value of N.

2
3

For N

= 5, K = 1, 2, 3,4, 5

We enter 0 as the value of N.
The FOR loop is skipped because

"10

>N.

and so on.
Change one statement in the above program.
1 NP U T N
Here is the change.
.
FOR K=1 TO N
~
PRI NT .. *"~
---And we added this statement.
NEXT K ·
. If you want to know why, RUN
PRI NT
the program without it.
50 GOTa 10
99 END
We enter 3 as the value of N.
10
20
30
4£1
45

RUN

***
17

*******
and so on.

And the computer prints 3 asterisks.
We enter 7 as the value of N.
And the computer prints 7 asterisks.
Carryon-you pick the value of N.

1-52

Another example. Study it carefully.
10 INPUT A.. B
20 FOR X-A TO B
30 PRINT XJ
40 NEXT X
50 PRINT
60 GO TO 10

The semicolon packs 'em in.

99 END

RUN
13 .. 8
3

678

11 .. 13
1

Let's trace the above program for- A

= 3, B = 8.

OUTPUT

STATEMENT

B·

10 INPUT A, B

== A TO B 3

8
8

3
4

40 NEXT X

3
3

30 PRINT X;
40 NEXT X

3
3

30 PRINT X;
40 NEXT X

3
3

5
6

30 PRINT X;
40 NEXT X

6
7

30 PRINT X';
40 NEXT X

30 PRINT X;
40 NEXT X -

3
3

Sixth time
X> B. Stop the loop!

50 PRINT
60 GO TO 10

3
3

A carriage return

and a line feed.

10 INPUT A, B

and so on,

20 FOR X

30 PRINTX;

1-53

REMARKS

First time
X~B

Second time
X~B

Third time
X~B

Fourth time
X~B

Fifth time
X~B

Exercise 37. The following program directs the computer to
compute and print the sum and the arithmetic mean of N numbers.
Trace it.
1" READ N

s."

2" LET
30 FOR K-l TO-N

The value of N is in Line 90.

"" READ X

The values of X are in line 91.

50 LET S-S+X

60 NEXT K

70 PRINT

N~S

Here is the value of N. (See Line
10.) And here are the values of X.
Note that there are N values.

.. S/N

90 DATA 3
91 DATA 87 .. 73 .. 95
99 END

STATEMENT

OUTPUT

10 READ N
20 LET S= 0
30 FOR K = 1 TO N
40 READ X
50LETS=S+X
60NEXTK
40 READ X
50LETS = S + X
60NEXTK
40 READ X
50 LETS = S+X
60NEXTK
70 PRINT N, S, SIN
99 END

Exercise' 38. How would you modify the two DATA statements
to compute the mean of the numbers: 75, 66, 83, 75, 98?
90 DATA
91 DATA

1-54

Extra for Experts
The examples on this and the following page may help you discover more things about the FOR statement and how it is used.
We also encourage you to experiment-tryout your own ideas on
the computer. You may wish to guess how something works and
then try it out.
\

10 INPUT A,B,H
20 PRINT. "RADIUS","AREA"
30 FOR R-A TO B STEP H
40-PRINT R,3.14*Rt2
50 NEXT R
55 PRINT
60 GO TO 10

Compare!

99 END

RUN
12,8,3

RADIUS
2

(A= 2, B

AREA
12.56

The value of R is stepped from 2
to 8 in steps of. 3.

78.5

5
8

= 8 and H = 3)

200.96

Another example-another idea.
10
20
30
40
50
60

READ N
FOR K-N*N TO N*CN+l)
PRINT KJ
NEXT K
PRINT
GO TO 10
90 DATA 3,7

We can use any BASIC expression.
Note the semicolon.
Causes a line space. That is, prints
a blank line since there is no list
following the word PRINT..

99 END

RUN
9

10 11 11·
50 51 52

DATA ERROFf, AT LINE 10

1-55

Results for N = 3
Results for N = 7

We can have a loop within a loop.

10 PRINT ·'I""nJ9'
15 PRINT
20 FOR 1·-1 TO 2
30 FOR J-l TO 3 ]

]

--Inside loop

40 PRINT I"J
50 NEXT J
60 NEXT I

4!II......

-41..
__--

Outside loop

99 END

RUN
1

J
1

1
1
2
2
2

i J.. ~1

]

Inside loop

.......- - - Outside loop

.....
-..-- Inside loop

We can use a loop within a loop to print a pattern of M rows
with N asterisks in each row.

~--N

asterisks per row

......
11--

M rows

Try this program without the
PRINTS in Lines 60 and 80.
(7 rows, 12 asterisks per row)
Here they are. Seven rows of aster.....- - - - - isks with 12 asterisks in each row.

1-56

FUNCTION JUNCTION
The Integer (INT) Function

The integer (INT) function returns the value of the nearest
integer not greater than x. Let's see how it works.
10 PRINT

INT(0)~INT(1)~INT(e)~INT(3.14)~INT(7.99)

99 END

RUN

From the results, we see that:
INT(O) = 0
INT(3.14) = 3

INT( 1.) = 1
INT (7.99) = 7 .

INT(2)= 2

Here are some rules you can count on.

• If X is a whole number, then INT(X) =

.For example,
INT(O) = 0
INT(2)= 2

INT(I)= 1
INT(3)= 3

• If X is a positive number or zero, then INT(X) is the
whole number part of X.

For example,
INT( 123.45) = 123
INT(.75) = 0

INT(2.99) = 2
INT(O.75) = 0

Exercise 39. Complete the following.
(1) INT(4) = _ _ __
(2) INT(12345) = _ __
(3) INT(O.999999) = _ _

(4) INT(27.0l) = _ _
(5) INT( 12/4) =
4
(6) INT(13/5) = ___ 4

Evaluate the numerical expression first, then apply the INT function to
the result.
.

1-57

The INT function is useful in solving problems such as the fol- .
lowing.
Let a be a whole number and let b be a natural number. Divide b into a to obtain a whole number partial quotient, q,
and a whole number remainder, r.

For example, let a = 28 and b = 7.
Partial quotient, q

4
7

= 4.

(28
28

Remainder, r = O.

Next let's try a = 97 and b

=5~

Partial quotient, q

= 19.

5(97
5

47
45
2

Remainder, r = 2.

. Once more - this time a = 29 and b =

32.

Partial quotient, q

= O.

32/29

Remainder, r

= 29.

We can write a mathematical sentence relating a, b, q and r, as
follows.
a = bq

For example,

where 0
97

< b.

= 5 x 19 + 2

a= b xq

1-58

Note that r

< b.

Let's solve for r:

=a -

And let's remember that q is the whole number part of a/b. Here
is a program to compute q and r given input values of a and b.
10 PRINT ··A"~"B··~"Q"~"R" •
20 READ AlB
30 LET Q-INTCA/B)
40 LET R-A-B*Q
50 PRINT AIB~Q~R .
60 GO TO 20
70 DATA 281719715~29132
99 END
Note how we compute q and r.

RUN
B

7
5

01
2

4
19

DATA ERROR AT LINE 20

Exercise 40. Complete the following trace of the RUN of the
preceding program.
STATEMENT
. 10 PRINT "A","B","Q","R"·
20 READ A,B
30 LET Q INT (AlB)
40 LET R A - B *Q
50 PRINT A,B,Q,R
60GO TO 10

=
=

28
28
28
28
28

20READA,B
30 LET Q INT(A/B)
40 LET R A - B *Q
50 PRINT A,B,Q,R
60 GO TO 10

=
=

20 READA,B
30 LET Q INT(A/B)
40 LET R A - B *Q
50 PRINT A,B,Q,R
60GOTO 10

=
=

and so on.

1-59

7
7
7
7
7

4
4
4
4

OUTPUT

0
0
0

Exercise 41. Let x be a 2-digit whole number. That is, x is a
whole number such that:
10

We define a number y as follows.
y = sum of the digits 'of x.

For example,

= 10, then y = 1 + 0 == 1
if x = 25, then y = 2 + 5 =: 7
if x = 99, then y = 9 + 9 =: 18
if x

Complete the following program to compute y for a given value
of x. RUN it for the DATA shown.
10
20
30
40
50
70
80
90

READ X

PRINT X"Y
GO TO 10
DATA 10,,15,23,,37,,40,,99

99 END

Exercise 42. Let z be the number obtained by reversing the digits
of x. For example:

=
=

if x 10 then z = 01
if x = 37 then z = 73
if x 99 then z 99

Modify your program of Exercise 41 so that the computer computes the value of z instead of the value of y.
EXPLORE!
Try the INT function on negative numbers (non-integers as
well as integers). Can you give a general definition of the
INT function?
1-60

The Square Root (SQR) Function
We assume that you know how to compute square roots of numbers. Let's find out.
Exercise 43. Complete each of the following:
1. A square root of 4 is _--'--______________
2. Another square root of 4 is ______________
Here is how we instruct the computer to compute square roots.

10 PRINT
99 END

SQR(4)~SQR(25)~SQR(100),SQRC0)

RUN
10

If X is any non-negative number (positive or zero), then SQR(X)
is the non-negative square root of X. If you try to take the square

root of a negative number, you may obtain an error message.

10 PRINT SQRC-4)
99 END

Note the error message.

RUN
ARGUMENT ERROR AT LINE 10

The symbol SQRO which we use in BASIC corresponds to the
symbol r" which we use in mathematics. Perhaps you recall that,
is used to mean the non-negative square root of a.

-Va

is used to mean the negative square root of a when
a

>,0.
1-61

Here is a program to compute the two square roots of a.
10
20
30
99

INPUT A
PRINT SQRCA),-SQRCA)
GO TO 10
END

RUN
14
-2

14096
64
10

12
1.414214

-64

o
-1.414214

By using the FOR-NEXT
root table.
10
20
30
99

If a

= 0, there is no negative square

root.
These answers are approximations
to the square roots of 2.
loop~

you can build your own square

FOR X-I TO 10
PRINT X,SQR(X)
NEXT X
END

RUN
1
2
3
4
5
6
7
8
9

1.414214
1.732051
2

2.236068
2.44949
2.645751
2.828427
3

3.162278

To obtain the square root table of
your choice, modify the FOR statement.

Exercise 44. How would you write the FOR statement to obtain
a square root table with values of X running from 0 to 1 in STEPS
of.2?

1-62

If we know the lengths of two sides of a right triangle, we can
compute the length of the third side by applying the Pythagorean
theorem. For example, suppose c.is the length of the hypotenuse
and a and b are the lengths of the other two sides, as indicated in
the diagram.
Given a and b, we want to comp~te c.

C=,Ia>+~b
a

Let's use the computer.
10
20
30
40
90
99

READ A"B
LET C-SQRCAt2+Bt2>
PRINT A"B"C
GO TO 10
DATA 3,,4,,12,,5,,1,,1
END

{Data for 3 triangles)

RUN
3

5
1

1.~14214

DATA ERROR AT LINE 10

From the results we see that
If a = 3, b = 4 then c == 5
If a = 12, b = 5 then c = 13
If a= 1, b = 1 then c = 1.41421
Exercise 45. Suppose we know the values of c and a. You write
the program to compute and print the value of b. Then use your
program to obtain the value of b for each of the _following.

- 1-63

LOOK BOTH WAYS

LOOK BOTH WAYS
Look back-where have we been?
Loops

SCR

FOR

SQR

expressions

LET

INPUT

variables

INT

LIST

floating point

READ
PRINT

messages

RESTORE

END

DATA

RUN

Look ahead-more BASIC-·where will it lead?
IF

RND

ABS

COS

STOP

ATN
REM

RETURN
ON ... GOTO
Subscripted variables

SGN

DIM
Arrays

flow charts
DEF
1-64

LOG

TAN

GOSUB
SIN
EXP

FINDING YOUR WAY
Flowcharts
A flowchart is like a road map. A road map helps you find your
way through unfamiliar terrain-a flowchart helps you find your
way through a computer program. If you want to, use a road map,
you must learn how to read it-true also of a flowchart. We will
start with easy flowcharts and show you how to r.ead them. Here
is a flowchart of'a program to generate 'counting numbers.

When you read a program
follow the line numbers.

When you read a flowchart,
follow the arrows.

10 LET K-l
20 PRINT K
30 LET K-K+l
40 GO TO 20
99 END
,;'

,,;'

Note that this arrow corresponds to the GO TO statement. In
this flowchart there is no box corresponding to the END statement.

If you prefer, you can draw horizontal flowcharts instead of

vertical flowcharts.

LETK=1

~4. . _L_E_T...,K_r--K_+_'_~1

~31

"..--...,

1-65

Here is a flowchart with an END box.

LET R=3

LET A-3.14*R'2

~10-LE-!~R-_3~ ~

~ PRINT R,A

20 LET A-3.14*Rt2 '
30 PRINT R,A------------~

END--------------------------~

In the above flowchart, we showed the END box because it is
actually executed in the program, causing the computer to stop.
What next? An INPUT box.

10
20
30
40

INPUT R
LET A-3.14*Rf2
PRINT R,A
GO TO 10

99 END

This END is never actually
executed by the computer; so
we don't show it in the flowchart.

Note the shapes of the boxes used in the :Ilowchart so far.

From now on, we will usually omit this reminder.

1-66

Confused? More examples may help.

13 INPUT A,B
LET Q-INTCA/B)
37 LET R=A-B*Q

PRINT A,B,Q,R

52 GO TO 13
99 END

RUN
779,12
79

? and so on.

To save space, we might do the
above flowchart like. this

or like this

INPUT A,B

We simply put two LET statements in one
LET box in order to save space. If there
are two or more statements in a box, execute
them in order from top to bottom.

1-67

Exercise 46. Below are flowchart boxes in the order in which we
introduc.ed them. Note the shape and write the type of box (INPUT, END, LET, etc.) beneath each shape.

C
_ _)

How do we indicate a GO TO statement in a flowchart?

----

..
Exercise 47. Complete the flowchart of the following program.

C--,-_
10 INPUT AID
20 PRINT A
30 LET A-A+D
1&0 GO TO
99 END

Exercise 48. Write the program that corresponds to the following
flowchart. Use our line numbers.
12

-----------------------

---------------------------------------------------48
-------------------------36

----.--------------------

99
LET K= K+1

What does the program do? That
is, what does it direct the computer to do? Predict the results,
then RUN the program on the
computer.
1-68

We use the same box shape for READ as we do for INPUT.
But there is no flowchart box corresponding to a DATA statement.

10 READ A~B
20 LET C-A*B
30 PRINT A,B .. C
40 GQ TO 1090 DATA 3~I&~S~-7
99 END

RUN
3
5

-7

-35

DATA ERROR AT LINE 10 -

Let's put the computation
directly into the PRINT
statement (program) or the
PRINT box (flowchart).

10 READ X,N
20 PRINT X~N .. X+N
30 GO TO -10
60 DATA 2 .. 3,10,10
99 END

RUN
2
10

DATA ERROR AT LINE 10

Remember: Use

C
______)
1-69

for either INPUT or READ.

Messages? How do we show them in a flowchart? Easy . . .

10 PRINT "GOOD MORNING t '
99 END

Note the quotation marks.

Another example10
20
30
40
50

PRINT "RADIUS", t'AREA"
READ R

PRINT R,3.11&*Rt2
GO TO 20
DATA 2,3,8

99 END

RUN

RADIUS

AREA

12.56
28.26
200.96

2
3
8

DATA EUROR AT LINE 20

If you don't like OUf style of flowchart, invent your own. Like ...

~~CATCH

ANSWER

1-70

FOR-NEXT Loops in a Flowchart
,

Remember FOR-NEXT loops? We show them in a special way
in a flowchart.
10

FOR Klill TO 5 -

FOR

- 20 PRINT KJ

K =1 TO 5

30 NEXTK
99 END

RUN
PRINT K

NEXT K

Another one-this time with
a STEP clause.

10 FOR E-e TO 10 STEP 2
PRINT E
39 NEXT E
99 END

FOR

E-0 TO 10
STEP 2

RUN
PRINT 'E

o
2
1.&

6
8

NEXT E

We include the END box in the flowchart above because it is
actually executed-stopping the computer after all numbers specified by the FOR-NEXT loop have been printed.
1-71

Exercise 49. <;omplete the flowchart of the following program.

10 INPUT A.,.B"H
20 FOR X=ATO B STEP H
3~ PRINT X
40 NEXT X
50 GO TO 10
99 END

Exercise 50. Draw··a flowchart of the following program. Draw
your flowchart here. ~
10
20
30
49
50

INPUT N
FOR Kul TO N
LET P-KtK
PRINT K"P
NEXT K

99 END

RUN
15
1
2
3
1&

1
4
27
256
3125

K t K increases rapidly,
doesn't it?!

1-72

MAKING DECISIONS
A Fork in the Road
The road divides into two paths ... which way?

...

This way?

--------< ,

or this way?

You must decide;
In a flowchart we use a diamond shaped box to indicate a decision point based on a condition.
One arrow into the box

We write the
condition inside
the box.

YES

Two arrows out of the boxone labelled "YES" and.
one labelled "NO"

The condition in the box must have exactly two possible outcomes.
• If the condition in the box is TRUE, follow the arrow

labelled YES.
• If the condition is FALSE, follow the arrow labelled NO.

Examine the condition in the decision box above and complete
the following table showing which path to follow for given values
of A andB.
Value of A
3

Value of B

4
2
7
1
,-1

-2

-1

5
7

Which Path? (YES or NO)

1-73

Which is larger, 3 or 41
Which is larger, 5 or 21
If A

= 3 and B = 4, which is larger, A or B1

If A

= 5 and B = 2 which is larger, A or B1

.._ _ _ _ _ __

In the flowchart below, trace the path for A = 3, B = 4 and the
path for A
5, B
2. You may wish to mark these paths in two
different colors.

PRINT A

The flowchart directs the
computer to print the larger
of two numbers, A and B.

Suppose you mark the path for A
3, B =: 4 with a red pencil
and the path for A
5, B
2 with a green pencil. Which path
would we follow (red or green) if

= 0, B = 21 _ _ _ _ __
A = 7, B:= 71 _ _ _ _ _ _ _ A = - 1, B == =- 21 _ _ _ __

A = 1, B

= 01 ____

._ _ _ A

Let's translate the flowchart into a BASIC program.
1-74

10 INPUT A,B
20 IF A>B THEN 50 ~---t
30 PRINT B~
40 GO TO 10
. 50 PRINT A
60 GO TO 10
99 END

This is an IF statement. It corresponds to a decision box in a flowchart.
... Fol1ow me if and only if A> B.
Prove it! RUN the program.

RUN
13,4
4
15,2
5

If A

A =3,B.=4.
JJ is larger than A.
A = 5, B = 2.
A is larger than B.

= 3 and B = 4 the computer executes statements 10, 20,

30 and 40.
If A

= 5 and B = 2 the compu.er executes statements 10, 20,

~
50 and 60.
Let's trace the program. We follow the computer as it executes
each statement and show the values of A and B after each statement is carried out. For a PRINT statement, we also show what is
printed under the heading "OUTPUT."

STATEMENT

B OUTPUT

10 INPUT A,B

20 IF A> B THEN 50
30PRINTB

3
3

4
4

4000 TO 10
10 INPUT A;B .

20 IF A> B' THEN 50
50 PRINT A

5
5

2
2

60 GO TO 10
10 INpUT A,B

20 IF A>B THEN 50
30 PRINT B

7
7

REMARKS

First case: A
3,
B = 4.
A>B is FALSE.
Continue with Statement 30.
Go around again.
Second case: A = 5,
B=2.
A>B is TRUE.
Go to Statement 50 and
proceed.
Go aroul1d again.
Third case: A
7,
B = 7.
A>B is FALSE.
Continue with Statement 30.

40 GO TO 10
and so on.

1-75

Exercise 51. Complete the following program and flowchart directing the computer to print the smaller of two numbers, A and B.

10 INPUT
20
30 PRINT
40 GO TO
50 PRINT
60 GO TO
99 END
RUN

A,B
B

A
PRINT A

13.4
3
15.. 2
2

Exercise 52. We have written a program directing the computer
to print two numbers in ascending order with the smaller on the left
and the larger on the right. You do the flowcbart here;

10 INPUT A.B
20 IF A B and set C = A.

B is TR VE, our guess is
correct. In this case, follow the
YES path.

But if C ~ B is FALSE, we were
wrong. We acknowledge our mistake and set C B.

By either path,
C
MAX(A, B)
'maximum of
A and B. So we print the value of

Again, there are two possible paths through the flowchart. Mark
them in two colors. If you mark the path for A= 3, B = 4 in green
and tne path for A
5, B
2 in red, which path (green or red)
should we follow if

= 2, B = I? _ _ _ _ _ _.::-- A = 9, B = 10? _ _ _ _ __

A =7,B= 71 _ _ _ _ _ _ _ A =O,B= -1 1·

1-77

~~_ __

O.K., here is the BASIC program to go with the flowchart on the
preceding page.
Note how we write
statement.

10 INPUT A, B

20 LET C=A
30 IF C>=B THEN 50
40 LET C=B
50 PRINT C'"

60 GO TO
99 END

~ In

an IF '

. . . . . Follow me if and only if
C

= 3,B = 4.

B is TRUE.

RUN

C=4.

13,4
4
15" 2
5

A
5, B
C=5.

= 2.

Your turn ... complete the following trace of the above program.

STATEMENT

ABC

10 INPUT A,B

20 LET C;:j A

3..

30IFC> ::::tBTHEN50

OUTPUT

REMARKS

~ "",3
4

40LETC =B

B is FALSE.

Yau carryon.

50PRINTC

60 GO TO 10
10 INPUT A,B

20LETC-:A

5...

30 IF C

B THEN 50

~ ,..5
2

1-78

TRUE or FALSE?
Where to next?

The IF Statement

The IF statement directs the computer to examine a relation between two expressions and then follow one (and only one) of two
paths depending on whether the relationship is TRUE (YES) or
FALSE (NO).
In general, the IF statement looks like this:

where

= line number of the IF statement

= any BASIC expression

THEN

e;!

e;! =

any BASIC expression
r
anyJegal BASIC relation (see below)
t = line ~umbef of th'e statement executed next
if and only if el r e;! is TRUE

Relation between
.~
two expressions, el and e2 ~
For example,
35

INT(X)

THEN

t IFt t tr
n

is TRUE if X is an integer.
X = INT(X)
is FALSE if X is not an integer.
Here is a handy table showing BASIC relations and corresponding mathematical ralations.
MATH

<
>
~
~

:f=

BASIC

RELATION

<
>
<=
>=
<>

Equal to
Less·than
Greater than
Less than or equal to
Greater than or equal to
Not equal to

1-79

A Problem. Write a program directing the: computer to tell us
whethe,r a n;umber is positive, negative or zero.
Let's solve it. Since there are three possibilities (X > 0, X < 0,
or X
0),: we can't solve the problem with a single IF statement.
But we can do it with two IF statements.

For example,

If X > 0 is FALSE, then
X < 0 or X= O. Which
one?

There are three possible paths through the program. Mark them
in three colors.
What color path if X

= 7? _ __

What color path if X

= - 3?_ __

What color path if X = O? _ __
Exercise 53. Write a BASIC program to go with our flowchart.
RUN nfor X
7, X
-3 and X
O.

1-80

VARYING PATTERNS
Rectangular Patterns
We wrote a program to print rectangular patterns on the Teletype. We ran it ... here is what happened.

Rows

?12.29~~
__--------------------

*****************************
*****************************
*****************************
*****************************
*****************************
*****************************
*****************************
*****************************
*****************************
-*****************************
*****************************
*****************************

Columns
Our program lets us specify the
number of rows and columns in this
rectangular pattern.
This pattern has 12 rows and 29
columns. That is, it has 12 rows
and there are 29 asterisks in .each

row.

Using our program, we can direct the computer to print rectangular patterns with as many rows as we want. The number of
columns, however, is limited to 72 since there are only 72 printing
positions across the paper.
In the above pattern, there are
12 x 29 = 348
asterisks in all.
Let's RUN the program again.
13, 10 .........-------------This time we want 3 rows,

columns.

**********
**********
**********

Here they are . . . count them.

Now let's look at the program.
1-81

Below is part of the program. This part directs the computer to
print one row of asterisks with N asterisks in the row.

10 INPUT N
15 PRI NT

N specifies the number of asterisks
to be printed in the row.
Here is the heart of the program. It
causes the computer to print N
asterisks, all in one row because the
PRINT statement ends with a semicolon.

30 FOR C: 1 .TO N
40 PRI NT "*";
50 NEXT C

60 PRINT
80 GO TO 1,0
99 END

This PRINT causes a carriage return and line feed to occur after all
the asterisks have been printed.

RUN

Let's try it.

110

= 10, so
the computer prints a row with 10
asterisks.

**********
120

N=20,

********************

How many asterisks?

172

= 72. Computer prints 72 aster-

isks.

= 73 , . , can't get them all on
one line',

************************************************************************
175
************************************************************************

The 73rd asterisk ended up

h~re.

The computer will print up to 72 asterisks on one line ... but
no more. If N > 72 then the computer prints 72 asterisks on the
first line and continues on the next line. Suppose N = 200. How
many lines
it take to print the "row" of 200 asterisks?

will

1-82

By adding three statements and changing the INPUT statement
in the preceding program, we get a program to print a pattern consisting of M rows with N asterisks in each row.
10 INPUT M,N
15 PRIr'lT

Which lines did
we add?

20 FOR R"l TO M

30 FOR c~ I TO N
40 PRINT n*n.:

One row with·
N asterisks

50 NEXT C

M rows

60 PRINT
70 NEXT R

\
75 PRINT
80 GO TO 10
99 END
RUN

This program has a "loop within a
loop."
Does it work? RUN it.

= 5, N = 12.

15,12

We enter M

************
**********~*
************
************
************

The computer prints a rectangular
pattern with 5 rows and 12 columns.

1 1,7

A 1 by 7 pattern (1 row, 7 columns).

*******

*
*
*
*
*

And a 7 by 1 pattern (7 rows, 1
column).

We finish with a 1 by 1 pattern.

*
P .S. How about a null (empty)
pattern?

1-83

Exercise 54. If you are tired of seeing asterisks before your eyes,
change this 'Statement ~

40 PRINT

to this_
.

.... 40
~40
r

or t hIS---

""'''J

PRINT "X" J
PRINT "I'"

or to the statement of your choice. Then RUN the program again.
Exercise 55. Start with our program on page 1-83. Change the
INPUT statement to
•

10 INPUT M

and change one other statement so that the modified program will
print right triangular patterns, like these.
RUN

----

-------1
I

This pattern ~as 2 rows with, 1
asterisk in Row 1 and 2 asterisks in
Row 2.

12Ar

!3~·~--------------------------'--~1

**
***

-~.-

This pattern has 3 rows with 1
asterisk in Row 1, 2 asterisks in
Row 2 and 3 asterisks in Row 3.

_______________________________

**
***
****

--,

This pattern has 4I rows with 1 asterisk in Row 1, . . .

and so on.
For an INPUT value of M, the pattern has M rows with 1 aster- .
isk in Row 1, two asterisks in Row 2, three asterisks in Row 3,
... , M asterisks in Row M.
1-84

In the following program, we use a "brute force" approach to
tell the computer to print a "leaning tower" pattern.
10 PRINT "********"
20 PRINT " ********"
30 PRINT" **"''''****''
40 PRINT"
********"
50 PRINT "
**",***",,,,,,
60 PRINT "
"''''*'''****''
70 PRINT ..
"'****"'*"'''
80 PRINT "
*******"'''

Each PRINT statement tells the
computer to print a certain number of spaces followed by 8 asterisks.

99 END

spaces
RUN

. . *"'**"'**'"
*"''''**'''''''''
"''''**'''***
********
********
. ********
********
********
\

You can use the·" brute force
method to print just about any
pattern you wa~t.

spaces

Let's make the tower lean the other way ..'
10 PRINT ..
20 PRINT "
30 PRINT "
40 PRINT "
50 PRINT"
60 PRINT."
70 PRINT"
80 PRINT "
99 END

********"
********"
********"
********" Print 7 spaces, then 8 asterisks.
********"
Print 6' spaces, then 8 asterisks.
***",***",,,
And so on.
********"
"'**"'**"'*"

RUN

*******'"
",**",,,,*,,,,,,.
********
********
"'***"'**'"
"'**"'''''''**
***"'''''''*'''
*******"',

1-85

The TAB Function
Yes, we're leading up to something . . . here is another way to
do the first leaning tower pattern.
10 PHINT TAB(0);"********"

20 PRINT TAB(1);"*** ••••• "

30 PRINT TAB(2);"** •• ***."
40 PRINT TAB(3)J"******.*"
50 PRINT TAB(4);"*.**** •• "
60 PRINT TABCS)}"******.*"
70 PRINT TAB(6);"* •• ***.*"
80 PRINT TAB(7);"****.***"
99 END

RUN
********
* •• **.**
*.******
.* •• *.**
********
*.*** •••
********
***.** ••

We wrote this program primarily ...
to introduce the TAB function.
The TAB function causes the computer to spaee over to the printing
position enclosed in the ( ).

We hope your version of BASIC provides the TAB function ...
if n9t; you might as well skip the rest of this section. fi If your computer does provide the TAD function, read on!
EXAMPLE

EXPLANATION

TAB(7)

Space the teletypewriter over to printing Position 7.

TAB(25)

Space the teletypewriter over to printing Position 25.

There are 72 printing positions across the page . . . they are
numbered through 71.

****************************************************
'pOSit jon

Position 37

Position 71

Your turn ... circle printing Positions 10, 20, 30, 40, 50, 60
and 70 above.

EduSystem 10 does not include the TAB function; larger systems do.

1-86

In general, the TAB function looks ]ike this
TAB(e)
where e is any BASIC expression. The expression is evaluated and
the computer spaces the Teletype to the position specified by the
value of the expression. If the value of e is not a whole number,
then the computer ~paces the teletype to the whole number part·
of the value of e.

EXAMPLES

EXPLANATION

TAB(K)

Move to Position K.

TAB(R - 1)

Move to Position R -1.

TAB (2*X + 3)

Move to Position 2*X

K ~ 71)

+ 3.

R -1
~

71)

2*X + 3

71)

Here is yet another way to print the leaning tower pattern.
10 FOR R= 1 TO 8
1 ).:
20 PRINT TAB(
30 NEXT R
T
99 EN D
.
RUN

RI.

********
********
********
********
********
********
********
********

u********"
.

Space over to printing Position
R - 1. When R
1, this is Position 0; when R = 2, this is position
1; and so on.

The computer cannot space the
Teletype ;
FOR C= 1 TO 8
PRINT U.";
NEXT C
PRINT
NEXT H
END

20
30
40
50
60
70
80
99

FOR R= 1 TO 8
PRINT TAB(8-R);
FOR Co: 1 TO 2.R-l
PRINT ".";
NEXT C
PRINT
NEXT R
END

Exercise 58. By adding an INPUT statement and changing a few
things in the programs of the preceding exercise, you can get a pr

• • • • .. • • ••••• • ••••• • *

probability of printing a star
is Y2. The probability of printing a
space is 1/2 •

Let's look more closely at statement 35.
35 IF

INT(2*RND(O))

THEN 50

The possible
values are 0
and 1 . - - - The following statement will also do the job. Try it!
35 IF

Because

RND(O)

< 1/2 THEN 50

~RND(O) < .5 is TRUE about V2 the time.
RND(O) <.5 is FALSE about 1;2 the time.'
1-94

In the following pattern the probability of printing a star is 1/10
and the probability of printing a space is 9/10. LOOK FOR CONSTELLATIONS ... MAKE UP YOUR OWN ... ARE ANY
SIGNS OF THE ZODIAC HERE?

142,65

*
**
*
* **
**
* *
*
*

* *
**
*
* *
*
*
*

*
*
*'
*

•• **. *

* **
** *
*
*
*
**
**...
*
...

*
*

**
*
*
*
*
*

*
**

**
*
*

* *
*
*

*
*

*
* *

*
*
* *
**

*
**
*
* *
** *
*
* *
* * *
*
**
*
*
**
*
*
*
**
*
** *
*
*
*
* **
**
*
*
**
*
*
* * *
*
*
*
***
* *
*
*
*
* * *
**
*
**
* * * **
* *
*
*
*
* *
* *
* '" *
*
* * *
**
*.*
•
...
**
*
**
*
* * *
** *
*
*
**
* * • ... *
**
* ,.; **
** ... *
*
*•
...
*
...
...
** •
... * *
... ***... * *...
*
* * •
... •• *
• *
* *... ...*
...
**...
* * *
*
...
*
*
*
* ...

*
*

* ** * *
*

>I<

Did you look at it from the left? The right? The top?
1-95

Exercise 63 . Write a program to generate random patterns like
-the one on the preceding page. You can do it by changing one
statement in our program on page 1-94. RUN it-look for constellations.
Exercise 64. Modify your program of the preceding exercise so
that the probability of printing a star is 1/20 and the probability
of printing a space is 19/20. RUN it-look for constellations.
Exercise 65. Why not enter the probability of printing a star
along with M and N? Begin your program with the statement
10 INPUT M, N, P
where
M is the number of rows,
N is the number of columns, and
P is the probability of printing a star.

But note: P must be entered as a decimal numeral such as .5 or
.1 or .05.
Here is a RUN of our program.

120,65,.1

*
**
*
* **
**
* *
*
*

*
*

* *
**
*
* *
*

*
*
*
*
*

*
*

**
*
*
*
*

* ** * *
*

*
**
**
*

'"
*

**
** *
* *
**
*
*
*
* * *
**
*
*

1-96

* *
*
*

**
* *

*
*
*

*
*
*
*

*
*

*
* *

*
*

*
**
**

* *
**
**

*
* * -

*
*

LITTLE BOXES
Remember . . . in BASIC, a variable refers to a location in the
computer's memory. You can think of the variable as the name
of the location.

1-1_. . .

variable/ : /
location"/'

A location is a "box" in which we
can store a number.

Here is a box (location) with a number in it.

The number in the location is the
value of the variable. (The value
of A is 37.)

Subscripted Variables
Are you acquainted with subscripted variables?
Here is a sUbscripted variable

This is the SUbSCriPt------

The symbol 'xa' is read 'x sub 3.'
Here are some additIonal examples of subscripted variables.

Read 'a 1 ' as 'a sub l'
Read 'C7' as 'c sub 7'
Read 'r2' as 'r sub 2'
and so on.

1-97

In BASIC, we can use subscripted variables, but we write them
in a slightly different way. Like this:
Here is a BASIC subscripted variable--------••X(3)
This is the subscript

------1

The subscripted variables X ( 1 ), X (2) and X (3) each correspond to a location
X(l)D

X(2)D

X(3)D

Exercise 66. LET X(l) = 73. In other words, take pencil in
hand and write the numeral "73" in the box labelled" X (l ) ." Then
do the following in similar fashion.
(l)

LET X(2) = 67

(2)

LET X(3)

= 85

Suppose that X ( 1 ), X (2) and X (3) are scores obtained on
three quizzes. Here is a program to compute and print the average
score (the arithmetic mean of the three scores).
1 0 LET X ( 1 )". 7 3
12 LET X( 2)=67
14 LET X( 3)-85
20 LET S=X(1)+X(2)+X(3)
30 LET M-S/3
40.,."PRINT M
99 END
RUN

Quiz 1. The score is 73.
Quiz 2. The score is 67.
Quiz 3. The score is 85.
Add the three scores, then divide
the sum by 3 and print the result.
Yes, we know you can write a
shorter program . . . but did you
learn anything about subscripted
variables?

1-98

Here is a better program.
INPUT X( 1>.X(2).X(3) ~
LET S=X(1)+X(2)+X(3)
LET M=S/3
.
PRINT M
50 PRINT
With
60 GO TO 1 0
three
99 END
RUN
10
20
30
40

?73.67.85~~.---------------~

this program, we INPUT the
scores.

x (1)1

--II

7_3

L...._ _ _

X(2)

6_7......1

X (3)

1L-_ _ _8_5 ......1

L -_ _ _

..........- - - - - - - - - - - O.K., enter your scores.

Exercise 67. Complete the following program to compute and
print the arithmetic mean (average) of four scores:
X ( 1 ), X (2), X (3) and X ( 4 )

10 INPUT
20 LET 5= _ _ _ __
LET Me _ _ _ __
~0

40 PRINT M
50 PRINT
60 GO TO·
99 END
RUN

R UN your program for the following sets of data. Each set consists of
four scores.

73,67,85,83
82,88,97,90

?
1

SHOW THE RESULTS
OF THE RUN

1-99

Next, let's change our program so that the data is called in by
means of a READ statement instead of an INPUT statement.
10
15
20
30
40
60
80
81
82
83
99

PRINT "XC 1 ) It, "XC 2)", "XC 3)", "MEAN'"
READ XCl),XC2),XC3)
LET S-X(1)+XC2)+XC3)
LET M=S/3
PRINT X(1),XC2),XC3),M
GO TO 15
DATA 7 3 , 6 7 , 8 5 } DATA 82,88,97
Four sets of data. Each. set has
DATA 93,89,95
three scores.
DATA 17, 11 , 61
END

RUN
XC 1>
73
82
93
77

X(2)
67
88
89
71

XC 3)

85
97
-95
67

MEAN
75
89
92.33333
71.66661

DATA ERROR AT LINE 15

Exercise 68. Change the above program to a program to compute and print the mean of four numbers X ( 1), X (2), X (3), and
X ( 4 ). Show the modified program below along with a RUN for
the following sets of data:
73,67,85,83
82,88,97,90

1-100

Generalizing
But what if there are five scores or six scores or se~en scores?
Shall we write a separate program for each case? Why not write
one program that takes care of any number of scores ... let's try.
We want to write a program to compute the arithmetic mean of
N numbers (quiz scores, golf scores, measurements ... you name
it). Since we have N numbers, let's call them
~

X(l), X(2), ... , X(N).

We tried the following program but it didn't 'work. We kept
,getting error messages.

10
20
30
10
20
30
40
50
60
70
71
72
73
99

READ N
Our computer didn't like these two
READ X(1),X(2),. •• , X ( N ) : : 7 statements.
LET.S-X(I)+X(2)+ ••• "LI5T
READ N
READ X( 1 )"XU3),,000,,'X(N)
LET S=X N. Therefore the loop terminates.
1-103

Exercise 69. Let's continue the trace that we began on the preceding page. We will show the statements; you fill in the K, Sand
M columns. Remember ... we left X( 1), X(2) and X(3) as
follows.
X(1)[_ _
73__

1 __67__1 X(3)1_____85_1

X(2) ___

STATEMENT

30LETS=O

33 FOR K

== 1

OUTPUT

35 LET S = S + X(K)
37 NEXT K

3
3

35 LET S = S + X (K)
37 NEXTK

3
3

35 LET S = S + X(K)
37NEXTK

3"
3

40 LET M = SIN
50 PRINTN, S, M
60 GO TO 10
and so on.

3
3
3

Exercise 70. For each program segment (portion of a program)
fill in the affected locations.

10 FOR N= 1 TO 4
20 LET peN )-2tN
30 NEXT N

70
75
80
85

LET F( 1 )
FOR Kc:2 TO 6
LET FCK)c:K*F(K-l)
NEXT K

P( 1)

P(3)

F(1)

F(3)

C]
C]

F(5)
1-104

D
P(4)
D
F(2)
D
F(4)
D
P(2)

F(6)

Subroutines
A new idea-subroutines-and three new statements, GOSUB,
RETURN, and STOP. Let's use them in a rewrite of the program
on page 1-103.
10
......... 20
30
40
50
60

READ N
GOSUB 100
LET M-S/N
PRINT N .. S.. M
GO' TO 10
STOP

-.~100

110
120
130
140
15&
160
110

FOR K-l TO N
READ X(K)
NEXT K
LET 5=0
FOR Kal TO N
LET S=S+X(K)'
NEXT K
RETURN

300
310
320
330
999

DATA
DATA
DATA
DATA
END

3 .. 13 ..
3 .. 82 ..
4 .. 13 ..
5,66 ..

main program

subroutine

61 .. 85
88",91
data
61 .. 85 .. 83
18 .. 11 .. 82,15

base

This program has a main program, one subroutine and a data
base. The subroutine in lines 100-170 is called by the GOSUB
in line 20.
Now, RUN the above program. The results should be the same
as for the program on page 1-99.
When the GOSUB in line 20 calls the subroutine, the computer
goes to line' 100 and executes the commands from line 100 to 160.
The RETURN statement in line 170 sends the computer to the
line following the GOSUB (line 30) that sent the computer to the
subroutine. The STOP statement in line 60 sends the computer to
the END statement, thus signaling the completion of the program.
A program may contain more than one subroutine. Suppose that
we wish to' print. headings for each of the columns printed by the
above program. We can do this by adding one statement to the
main program and inchidin~ one more subroutine.
1-105

5 GOSUB 200

new main program statement

200 PRINT "N"" "S"" "M"
210 PRINT
220 RETURN

new subroutine

Now LIST the program and then RUN it.
5 GOSUB 200
10 READ N
20 GOSUB 100
40 PRINT N" S" M
50 GO TO 10
60 STOP
100 FOR K- 1 TO N
110 READ X(K)
120 NEXT K
130 LET S"'0
140 FOR K-l TO N
150 LET S-S+X(K)
160 NEXT K
170 RETURN
200 PRINT "N"" "s"" "M"
210 PRINT
220 RETURN
300 DATA 3,,73,,67,,85
310 DATA 3,,82,,88,,97
320 DATA 4,,73,,67,,85,,83
330 DATA 5,,66,,7S,,71,,82,,75
999 END
RUN
N
3
3
4

S
225
267
308
372

DATA ERROR AT LINE 10

(II

0
(II

A program may have many GOSUB's, each .of which go to the
same subroutine; this is especially helpful when the same (or similar) statements appear more than once in the same program.
When you use subroutines, keep them distinct from the main
program. This is normally done by placing them after the main
program. Remember that the last statement in the main program
must be a STOP or a GO TO (e.g., GO TO 999-the END
statement) .
1-106

SNOOPY AND THE RED BARON
It is 1976 and the candidates for President of the United States

are Snoopy and the Red Baron. We conducted a poll by asking
29 of our friends to respond to the following question.
Who should be President in 1976?
Circle the number to the left of the
candidate of your choice.
1.

Snoopy

Red Baron

You guessed it . . . we are going to write a program to direct
the c~mputer to count the votes for each candidate, Snoopy and
the Red Baron. First, let's record the 29 votes in one or more
DATA statements. Remember, each vote is a "1" or a "2."

91 DATA 2,1,2,1,1,2,2,2,1,1,2,2,2,1,1
92 DATA 2,2,1,1,2,2,2,1,2,1,1,1,2,2

Before continuing, we ask you the following questions.
How many votes did Snoopy get? _ _ _ _ _ _ _ _ _ __
How many votes did Red Baron get? ___________
Add the number of votes obtained by Snoopy and the number
obtained by the Red Baron. The total should be 29 . .'. if not,
check your work.

1-107

We think you answered the questions on the preceding page
as follows.
1. You counted the number of "Is" in the two DATA statements. The result is the number of votes obtained by
Snoopy.
2. Then you counted the number of "2s" in the two DATA
statements. The result is the number of votes obtained by
the Red Baron.
That's fine, but we are going to use a different method. First, we
define two subscripted variables and assign the value zero (0) to
each. Like this:

C(I)r=~

C(2) I_____ _0.......1

Then we read the 29 votes, one by one. If the vote (V) is a "1"
we increase the value of C( 1) by one. But if the vote is a "2," we
increase the value of C (2) by one. After we have rea,d all 29
votes, C ( 1) will contain the number of votes for Snoopy and C (2)
will contain the number of votes for the Red Baron. Here is the
program and the results of a RUN.

If you don't understand the pro10
20
30
40
50

gram, study the trace on the next
page.

LET C( 1 )=0
LET C( 2)=0
FO R K- 1 TO 29
READ V
LET C(V)=C(V)+1

60 NEXT K
10 PRINT C(I),C(2)
91 DATA 2 .. 1 .. 2,1, 1,2,2,2,1,1,2,2,2,1,1
92 DATA 2 .. 2,1, 1,2,2 .. 2,1,2,1,1,1,2,2
99 END

RUN
13

t..-------+L-----

vote count for Snoopy.

L , - - - v o t e count for the Red Baron.

1-108

Exercise 71. Study the following partial trace of our vote count, ing program and fill in the missing information under the K, V,
C( 1) and C(2) columns.

STATEMENT

10 LET C(1)= 0
20 LET C(2) = 0

C(1)

C(2)

0
0

30 FOR K = 1 TO 29

40 READ V
50 LET C(V) = C(V)
60 NEXTK

1
1
2

2
2
2

0
0
0

0
1
1

2
2
3

1
1
1

40 READ V
50 LET C(V) = C(V)
60NEXTK

3
3
4

2
2
2

1
1
1

1
2
2

40 READ V
50 LET C(V) = C(V)
60 NEXT K

40 READ V
50 LET C(V) = C(V)
60NEXTK

40 READ V
50 LET C(V) '= C(V)
60NEXTK

and so on.

1-109

Exercise 72. We conducted another poll, asking the same question. But this time, we asked 32 people to votle for Snoopy or the
Red Baron. Here are the votes.
1, 1, 2, 1, 2, 2, 2, 2, 1, 1, 2, 1, 1, 1, 1, 1
2, 2, 1, 2, 1, 1, 2, 2, 2, 1, 1, 1, 2, 1, 1, 2
Use our program to process the above data. You will have to
change Lines 30, 91 and 92.
Exercise 73. Conduct your own poll. Then use our program to
process the data. You will probably have to change Lines 30, 91
and 92.
Exercise 74. Figure out how to use the following program to
count votes. Change it to count the votes of either Exercise 68
or 69.

10 READ N ..
20 LET C(I)=0
25 LET C(2)=0

30 FOR K=1 TO N ~~~-----------------40 READ V
50 LET C(V)=C(V)+1
60 NEXT K
70 PRINT C(I) .. C(2)
90 DATA 29 ~
91 DATA 2 .. 1 .. 2 .. 1.. 112 .. 2 .. 2 .. 1.. 1.. 2 .. 2 .. 2 .. 1 .. 1
92 DATA 2 .. 2 .. 1 .. 1.. 2, 2, 2,1 .. 2,1 .. 1, 1 .. 2, 2
99 END
RUN

N votes

1-110

Value of N.

No Opinion
Here is a slightly different questionnaire.

Who should be President in 1976?
Circle the number to the left of the
candidate of your choice.
1. Snoopy
2.

Red Baron

No Opinion

We asked 37 people and got the following votes.
1,3,1,.2,3,1, J, 2,3, 1, 1,2,1,1,2, 1,2,2,2
2, 1, 3, 2, 2, 1, 2, 1, 1, 3, 1, 1, 2, 3, 1, 1, 2, 3
How many votes for Snoopy? _ _ _ _ _ _ _ _ _ _ _ __
How many votes for the Red Baron? _ _ _ _ _ _ _ _ __
How many No Opinions?_--------------TOTAL of above categories? ______________
Now we hav.e three categories, so we use three subscripted
variables.
C(l)

I___~]C(2)
Snoopy

Red Baron

C(3)

L...--_ - - - - - - '

No Opinion

Exercise 75. Change our program of Exercise 74 into a program
to process data such as the above (three categories instead of two) .
You will have to add a line to set C(3) to zero, change Line 70
and, of course, change Lines 90, 91 and 92.
1-111

Exercise 76. In a newspaper, the results of a poll might be presented in a table such as the following.

CANDIDATE

VOTES

PERCENT

Snoopy

46%

Red Baron

35%

No Opinion

19%

(% of total vote)J

Modify your program of Exercise 75 so that the results are
printed in a table like the one shown above.
Exercise 77. But suppose there are three candidates. For example, our questionnaire might look like this.

Who should be President in 1976?
Circle the number to the left of the
candidate of your choice.
1.

Snoopy

Red Baron

Lucy

No Opinion

Write a program to count votes obtained by using the above
questionnaire. Invent your own data . . . print results in a table
similar to the table in Exercise 76.
1-112

More Choices
We have used questionnaires with two choices, three choices and
four choices. In each case, the choices have been political candi-.
dates or a "No Opinion" category. Our categories don't have to be
political, however. Here are several questionnaires that you can use
to gather data. Do so . < • then use the program on the following
page to compute the results of each of. your polls.

Which breakfast cereal do
you prefer? Circle the
number to the left of your
choice.

What is your favorite musical group? Circle the
number to the left of your
choice.
1. Beatles
·2. Blood, Sweat and
Tears
3. Crosby, Stills, Nash &
Young
4. Jefferson Airplane
5. Lawrence Welk
6. Rolling Stones
7. None of the Above

1.
2.
3.
4.

Trix
Total
Cheerios
No Opinion

What is your favorite individual sport? Circle the number to the left of your choice.
1.
4.
7.
10.
13.
16.
19.

Badminton
Fencing
Handball
Roller Skating
Surfing
Track
None of Those
Listed

. 2.
5.
8.
11.
14.
17.

Bowling
Golf·
IceSkating
Snow Skiing
Swimming
Water Skiing

3. Boxing
6. Gymnastics
9. Karate
12. Squash
15. Tennis
18. Wrestling

If someone circles two or mOre choices, throw out their ques-

tionnaire ... our program can't handle this case.
1-113

Here is our program. The lines that begih with the word "REMARK" are remarks! They have no effect on the execution of the
program. You may insert a REMARK line wherever you please.
100
200
2110
220
-300
310
320
330
400
410
420
500
510
600
610
620
63~

640
7f60
710
720
730
900
901
902
903
999

REMARK***THE P~OPLE·S POLL
REMARK***M IS THE NUMBER OF CATEGORIES (M<:99)
Dlf1 C (99)~ Let's talk about this below.
READ M
R~MARK***SET C(l),C(2), ••• ,C(M) ALL TO ZERO
FOR K:l TO M
LET C(K):0
NEXT K
REMARK***PRINT A HEADING
PRINT "CATEGORY", "VOTES"
PRI NT
REMARK***THERE ARE N VOTES
READ N
REMARK***READ N VOTES AND COUNT BY CATEGORY
FOR K:l TO N
READ V
LET C(V):C(V)+1
NEXT K
RiMARK***PRINT RESULTS (M LIHES,2, NUMBERS P~R LINE)
FOR K:l TO M
PRINT K,C(K)
NEXT K
R Ef1ARK***BEGI N DATA LISTS
DA TA ..........- - - - - - - Put your value of M here.
DATA ...
Put your value of N here.
DATA ,.
Record your votes, beginning here.
END
Use as many DATA statements as

necessary.

*** O.K., now RUN it! ***
The statement

2.10 DIM C(99)

is a DIMension statement. 7 It tells the computer to permit subscripts of C up to and including 99. Without a DIM statement, the
largest permissible subscript is 10. We chose 99 arbitrarily. We
could have c;:hosen 25 or 100 or 150 or any limit we wanted.
7

Not necessary on EduSystems 20 or 25.

1-114

Generation Gap

Snoopy and the Red Baron ... a new questionnaire.

Q1. Who should be President in 1976'1 Circle the

number to the left of your choice.
1.
2.
3.

Snoopy
Red Baron
No Opinion

Q2. Circle the number to the left of the phrase
that describes your age group.
1. Under 30 years old
2. ·30 years old or older.

The first question has three possible responses (1, 2 or 3) and,
the second question has two possible responses (lor 2). Each
completed questionnaire gives us two numbers. For example,
/1,2

L__

A vote for Snoopy ... by a person 30 years old or older.
We conducted a survey. We asked 32 people to vote, therefore
we got back 32 pairs of 'numbers . , .64 numbers in all.
1, 2, 2, 1, 3, 2, 1. 1. 2. 2, 2. 2. 1, 1, 2, 1, 1,2,2,2,2,2, 3, 1
2,2, 1, 1, 1, 1,2,2, 1,2, 3,2,2, 2,2, 1, 1, 1, 1, 1, 1, 1, 1,2
1, 1, 1, 2, 2, 1, 1, 2, 2, 2, 1, 1, 3, 1, 1, 1
Begin here and circle or underline each pair of numbers. The first
number in each pair is the vote (1, 2, or 3) and the second number
in each pair is the age group of the voter,

How many people under 30 voted for Snoopy?
How many people 30 or older voted for Snoopy?
1-115

· Fortunately, BASIC permits us to use variables with two subscripts.
UNDER 30

30 OR OVER

Snoopy

C(1,I)

IC(1, 2)

Red Baron

C(2, 1)

.IC(2, 2)

No Opinion

C(3, 1)

IC(3,2)

Here is a variable with two subscripts:
First subscript - , - - - Second subscript _ _ _.L
Have you guessed the following?

= number of votes for Snoopy by people under 30.
C( 1,2) = number of votes for Snoopy by people 30 or over.
C ( 1, 1)

C(2, 1) = number of votes for Red Baron by people under 30.
Your turn. Complete the following.
C(2, 2) = _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
C(3, 1)

= ________________

C(3, 2) = _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
Here is our data again, copied from the prec:eding page. Use it to
fill in the boxes (C(1,l), C(I,2), etc.) at the top of the page. We
suggest that you look at each pair of nuinbers and, for each pair,
put a mark in the appropriate box. After you have used all pairs,
simply count the number of marks in each box and write in the
number.
1, 2, 2, 1, 3, 2, 1, 1, 2, 2, 2, 2, 1, 1, 2, 1, 1,2, 2,2,2,2, 3, 1
2,2,1,1,1,1,2,2,1,2,3,2,2,2,2,1,1, 1, 1, 1, 1, 1, 1,2
1, 1, 1,2, 2, 1, 1, 2, 2, 2, 1, 1,3, 1, 1, 1
1-116

Here is a BASIC program to count the votes. We have included
several REMARKS to describe what's happening.
'
100
200
210
220
230
240
250
300
310
320
330
340
350
400
410
420
430
440
450
900
901
902
903
999

REMARK***SNOOPY~RED

BARON AND THE GENERATION GAP
REMARK***PUT ZEROS IN THE BOXES
FOR 1= 1- TO 3
FOR J= 1 TO 2
LET .c

7
DIM--list of subscripted variables

The above DIM statement tells the computer that:
The subscript of A must me
The sUbscript of B must be

20.
30.

The first subscript of C must be

20.

The second subscript of C must be

The first subscript of D must be

The second subscript of D must be

12.

If you don't mention a subscripted variable in a DIM statement,

then the computer assumes that its subscript or subscripts must be
less than or equal to 10.
1-120

Below are two programs. RUN each program using the given
data. Describe to yourself. what each program does, then make up
your own data and RUN it again.
10
15
20
25
30
35
40
45
50
55
60
65
70
80
81
82
83
84
85
99

DIM K(50).Ae50)
READ N
FO R J- 1 TO N
READ KeJ)
Maybe you can figure
NEXT J
program does without
LET S:a0 .
it!
FO R J:a 1 TO N
READ AeJ)
lF AeJ)<>KeJ) THEN 60
LET S-5+ 1
NEXT J
PRINT S
GO TO 35
DATA 12
DATA 2.1.2. 3. 4~ 1.3.2. 1.4.4.1
DATA 2.1.1.3.4.1.3.1.1.3.4.2
DATA 2. 1~ 2. 3. 3. 1. 3~ 2. 1.4.4. 1
DATA 1.1.1,3,4.1.3,2.2,4.4,1
DATA 3,4.2, 1,4. 1,2,4, 3.4, I, 3
END

100
200
210
220
230
300
310

DIM X(30)
READ N
F'OR K-l TO N
READ XC K)
NEXT K
FOR J-l TO N-l
FOR K-J TO N
3~u. xeJ)-X(K)LISL_
100 DIM X( 30 ..
200 READ N
210 FOR K=l TO N
220 READ XCK)
230 NEXT K
300 FOR J=l TO N-l
310 FOR K-J TO N
320 IF X(J).M THEN 260
250 IF H=INTCH) THEN 252
251 GOTO 260
252 IF H>0 THEN 254
253 GOTO 260
254 IF H<4 THEN 280
260 PRINT "YOU CHEATED',I 'LL GI \IE YOU ANOTHER CHANCE. Jt
270 GOTO 215
280 LET M=M-H
290 IFM=0 THEN 410
300 REMARK***THE COMPUTER
310 LET R=M-4*INTCM/4)
320 IF R<>1 THEN 350
330 LET C=INT(3*RND(0»+1
340 GOTO 360
350 LET C=(R+3)-4*INT«R+3)/4)
360 LET M=M-C
370 IF M=0 THEN 440
375 PRINT
380 PRINT "I TOOK";C;"MATCHES"
390 GOTO 200
,,400 REMARK***SOMEBODY \/JON ( SEE LINES 290 AND 370>
410 PRINT
420"PRINT "I \NON'!' BETTER LUCK, NEXT TIME.
430 GOTO 100
440 PRINT
450 PRINT "O.K. SO YOU wON. LET'S PLAY AGAIN."
460 GOTO ,100
999 END
It

We show a RUN on the following page (we lost).
1-125

WE STAHT WITH 23 MATCHES. WHEN IT IS YOUR
TURN, YOU MAY TAKE 1,2, OR 3 MATCHES. THE
ONE wHO MUST TAKE THE LAST MATCH LOSES.
THERE ARE NOW 23 MATCHES
HOW MANY MATCHES DO YOU TAKE?? 3

Human (that's me)
takes 3 matches.
Computer takes 3 matches.

I TOOK 3 MA TCHES
THERE ARE NOW 17 MATCHES
HOw MANY MATCHES DO YOU TAKE?? 2
I TOOK 2 MA TCHES
THERE ARE NOw 13 MATCHES
HOw MANY MATCHES DO YOU TAKE?? 3
I TOOK 1 MATCHES
THERE ARE NOW 9 MATCHES

Quite illegal!

HOw MANY MATCHES DO YOU TAKE?? 4 /
.
YOU CHEATED! I ILL GI VE YOU ANOTHER CHANCE. We got caught!
HOw MANY MATCHES DO YOU TAKE?? 1
I TOOK 3 MATCHES
THERE ARE NOW 5 MATCHES
HOW MANY MATCHES DO YOU TAKE?? 2
I TOOK 2 MATCHES

Nice try, but again
/ 'we got caught.

THERE ARE NOW 1 MATCHES

HOW MANY MATCHES DO YOU TAKE?? 0
YOU CHEATED! llLL GIVE YOU ANOTHER CHANCE.
HOW MANY MATCHES DO YOU TAKE?? 2
YOU CHEATED! I'LL GIVE YOU ANOTHER CHANCE.
HOW MANY MATCHES DO YOU TAKE?? 1
I WON"! BETTER LUCK NEXT TIME.

Can you beat the computer? Try it!

1-126

Rounding a Number
Sometimes we want to round a number. If you don't know what
we mean by "round," study the following program and the RUN
of it.

10
20
30
40
50
60
70
-80
99

REMARK*** ROUND TO THE NEAREST INTEGER
PRINT" X....... X ROUNDED"
PRINT
READ X
LET R-INT=C9/5>*T+32
GOSUB 100
PRINT FNF'CX>
GOTO 10
STOP
REMARK***READ AND TEST DATA
READ X
IF X>-273 THEN 140
PRINT "INVAL I D DATA"
RETURN
DATA -'40,0,100,23,9,37,-274
END

RUN
-40
32
212
73.4
48.2
98.6
INVALID DATA
-461.2
DATA ERROR AT LINE 110

The DEF statement in line 10 defines a function FNF which
may then be used elsewhere in the program. Defined functions must
have three letter names, starting with FN. The format of the DEF
statement is as follows:
(line number)DEF FNF(T) = (9/5)*T + 32
argument
1-131

formula

argument

F may be any letter. The argument (T) has no significance but
must be; the same on both sides of the equal sign. The formula may
be expressed in terms of numbers, several variables, other functions
(INT, SQR, etc.), or mathematical expressions.
Om:e the function has been defined, it is called in the same
manner as other BASIC functions, e.g. FNF(X). Only one DEF
statement is permitted in an EduSystem 10 program. The larger
EduSystems allow multiple DEF statements in a program.
Exercise 86. Define a function to find the area of a circle. Remember that the formula is:
A

= 3.14xR2

or as we say in BASIC

3.14*R t 2

Use the function to find the areas of circles with radii of 6, 8,
and 12. Use the computer to check your answers.
PAST AND FUTURE BASIC
Look back ... you have learned a lot about the language called
BASIC.

• Direct Statements9 SCR, RUN, LIST
• Statements: PRINT, END, LET, INPUT, GO TO, READ,
DATA, FOR, NEXT, IF, DIM, REMARK,
GOSUB, RESTORE
• Operations: +, -, *, /, t
• Relations: =, <, >, <=~ >=, <>
• Functions: INT, SQR, TAB, RND
• Also: Numerals, numerical expressions, variables, variable
expressions, traces, messages, loops, flowcharts, subscripted variables
Briefly mentioned:
• The SIN, COS, TAN, and ATN functions
• The LOG, EXP, ABS, and SGN functions

A direct statement does not have a line number. It is executed immediately (when you press RETURN) instead of being stored in the computer's
memory for later execution. Some people use the term "immediate statement" i:qstead of "direct statement."

1-132

Now you can "say" simple things in BASIC, but you are not
yet fluent. As with any language, if you want to become fluent, you
must use the language and also learn more about it.
Look ahead . . . more to learn about BASIC . . . things that
we haven't covered at all or have only mentioned briefly.
• Statements

DEF, GOSUB, ON . . . GO TO ... , RESTORE, RETURN, STOP
• Logical Operations: AND, OR, NOT
• Functions: ABS, ATN, COS, EXP, LOG, SIN, TAN

The above are included in many versions of BASIC. But there
are also some hopped-up versions of BASIC that have additional
features. Look for:
• Strings and String Variables
• String Functions
• Files
Where do you look? For each EduSystem there is a chapter in
this handbook that describes the exact characteristics of the language for that EduSystem. The following chart summarizes the
BASIC statements, edit and control commands, and functions and
indicates the EduSystems on which they are available;

1-133

Table 1-1.

-I

BASIC Statements

Statement

Format

Description

Input/ Output
CLOSE
CLOSE
DATA

CLOSE
CLOSEf
DATA n 1 ,n 2 , ••• nn

GET

GET f,l,r

INPUT

INPUT V1 ,V 2 , ••• vn

INPUT#

INPUT#, V

KILL

KILL F$

LINPUT

LINPUT v$l! V$2"" v$n

LPRINT

LPRINT e1 ,e 2 , ... ell

Close open ouput data file.
Close file f.
Numbers n 1 through nn are
variables for READ.
Read record r, form as in
line 1, from file f.
Get VI' through VII input from
Teletype.
Get v (can be numeric and!
or string variable) from
input data file.
Delete a stored data file
named by F$.
Get long character string
from Teletype.
Print values of specified text
or expressions on line printer
or high-speed paper tape
punch.

.;:...

EduSystems
5 10 15 20 25 30 40 50
x
x

x
x
x

x
x

Table 1-1 (Cont.).

Statement

Format

Description

OPEN

OPEN f,n$
OPEN A$ FOR INPUT

Open a file named n$ as file f.
Open an existing data file
named by A$.
Create or reopen an existing
data file named by B$; x is
number of blocks reserved for
this file.
Open a file; go to line n if
unavailable.
Print values of specified text,
variables, or expressions.
Format control (, or ;).
Write data (numeric or
string) onto die output data
file ..
Write record r, form as in
line 1, in file f.
Read variables v 1 through
vn from DATA list.
Reset DATA pointer to beginning value.

OPEN B$ FOR OUTPUT,x

'","'"
'\.;)
""'"

BASIC Statements

OPEN-ELSE

OPEN fELSEn

PRINT eH e2 , ••• en

PRINT#

PRINT#,n

PUT

PUT f,l,r

READ

RESTORE

V1 ,V 2 , ••• vn

EduSystems
5 10 1,5 20 25 30 40 50
x
x
x

·x
x

x
x

Table 1-1 (Cont.).
Statement

Format

Description

RESTORE *

RESTORE$

" RESTORE$

Reset DATA pointer for
numeric data only.
Reset DATA pointer for
character string data only.
Delete file from disk storage.
Record data n l through nn on
mass storage file .

UN SAVE
WRITE

....
....w
I

BASIC Statements

UNSAVEf
WRITE n 1 ••• n1l

Transfer of Controls
GO TO
GOTOn
IF-GO TO
If el r e2 GO TO n

IF-THEN

ON-GO TO

IF el r e2 THEN n
IF el r e2 THEN x

ON el GO TO 11 ,1 2 , ••• l n

Loops and Subscripts
DIM
DIM v(d 1),v(dl'd 2 )

EduSystems
5 10 15 20 25 30 40 50

x
x
x
x

Transfer control to line n.
If relationship r between e 1
and e2 is true, transfer control
to line n.
Same as IF-GO TO.
I f relationship r between e 1
and e2 is true, then perform
executable BASIC statement.
Computed GO TO.

x x
x x

x
x

x x

Dimensions, variables subscripted.

x x

x
x

Table 1-1 (Cont.).

....
....w
I

-..J

BASIC Statements
EduSystems
5 10 1520 25 30 40 50

Statement

Format

Description

FOR-TO-STEP

FOR v=el TO e2 STEP e3

NEXT v

Set up program loop. Define
v values beginning at el to e2,
incremented by e3.
Terminate program loop increment value of v until v
(>e2).

Subroutines
GOSUB
ON-GOSUB
RETURN

GOSUBn
ON el GOSUB
RETURN

x
x
x

STOP

Enter subroutine at line n.
Computed GOSUB.
Return from subroutine to
statement following GOSUB
or ON-GOSUB.
Transfer control to END
statement.

Others
CHAIN
'CHAIN$

CHAINn$
CHAIN$A$

x.
x

CHANGE

CHANGE v1 , TO V2

DEF

DEF FNA(x)=f(x)
DEF FNA(x,y)=(x,y)

I~,I2'"

.In

Link to next user program.
Link to public library program
named in A$.
Change character string to
array of character codes.
Define a function.

x
x

Table 1-1 (Cont.).

BASIC Statements
EduSystems

.....
.....

Statement

Format

Description

5 10 15 20 25 30 40 50

END
LET

END
LETv=f

x
x

RANDOMIZE

RECORD

REMARK
SLEEP

REM text
SLEEPn

End of program.
Assign value of formula f
to variable v. The word LET
is optional.
Randomizes random number
routine.
Define the size and composition of record.
Insert a remark or comment.
Cause program pause for
n seconds.

V1 ,V 2 , ••• vll

x
x

Table 1-2.

-I

Command

Format

Description

BYE
CATALOG

BYE
CAT

CAT$

COMPILE

CO~name

Leave BASIC Monitor.
List names of user programs.
in storage ar~a.
List names of public library
programs.
Compile program in core,
save on disk.
Stop program execution,
return to edit mode.
Delete line n.
Delete line TI.
Delete lines n through m
inclusive.
Search line n for character c.
(See appropriate chapters for
instructions on use.)
List the data files stored by
this user.
List the public data files.
Return. to keyboard mode
after TAPE.

CTRL/C.

CTRL/C

y.)

BASIC Edit and Control Commands

DELETE

DELn
n

DELn,m
EDIT

EDIn
(c)

FILELOG

FIL

FILEIDG$
KEY

FIL$
KEY

EduSystems
5 10 15 20 25 30 40 50
x

x
x

x
x
x

x
x x
x'

x
x
x

x
x

Table 1-2 (Cont.).
Command

Format

Description

LIST

LIST
LISTn

List entire program in core.
List program starting at
line 11.
List line n only.
List lines n through m
inclusive.
List entire program, no
header.
List program starting at line n,
no header.
List program to line printer.
Clear core, request program
name.
Clear core, bring program to
core from storage area.
Clear core, request public
library program name, bring
program to coreo from storage
area.
Replace old file on disk with
version in core.
If name not specified, old
name retained.

LISTn
LIST n,m
LISTNH
LISTNHn

'"""
I

'"""

.j:::..

BASIC Edit and Control Commands

LLIST
NEW

OLD

OLD$

REPLACE

REP
REP name

EduSystems
5 10 15 20 25 30 40 50
x

x x

x
x

Table 1-2 (Cont.).

BASIC Edit and Control Commands
EduSystems

'"""
......

Command

Format

RUN

SAVE

RUNNH
SAVE name

SCRATCH

SCR

TAPE

TAP

UN SAVE

UNSAVEname

BATCH
~CHO

BATCH
ECHO

LPT
LENGTH

NAME

PTP

'"""

Description
Compile and run program
in core.
Same as RUN without header.
Store program named on
storage device.
Erase current program from
core.
Read paper tape; suppress
. printing on Teletype.
Delete program named from
storage area.
Commence batch processing.
Switch from printout to nonprintout mode or vice versa.
Print output on line printer.
Request number blocks to
store current program.
Same as NEW but does not
delete existing program.
Punch entire program on
paper tape.

5 10 15 20 25 30 40 50
x

x
x
x

x
x

Table 1·2 (Cont.).
Command

Format

Description

PTR
PUNCH

Read paper tape.
Punch entire program on
paper tape.
Punch program starting at
line n.
Change name of program in
core.
Renumber program lines.
Print output on Teletype.
Enable use of privileged
commands.
Insert password, no echo.

PUNCH n
RENAME

REN

....

RESEQUENCE

TIY

TTY

PRIVILEGE·

PRIVILEGE

I-"
I

.j::>..

BASIC Edit and Control Commands

(password)
Privileged Control Commands
BATCHn
BATCH
HEADER

HEADER
(header)

LOG

Same as BATCH, limit program runs to n.
Change header; type new
header (maximum 12 characters) for next batch run.
Print system log.

EduSystems
5 10 15 20 25 30 40 50
x
x

x
x
x

Table 1-2 (Cont.).

Command

Format

Description

MAX

MAXn

Set instruction limit n times
200 per program for next
batch run.
Change password, no echo.

..... PASSWORD
I

..-

..r;:..

BASIC Edit and Control Commands

SAVE
STACK

PASSWORD
'. (new password)
SAVE
STACK
STACKn

UN SAVE

Save program in storage area.
Start unattended batch
operation.
Same as STACK; limit runsl
program.
Delete program from storage
area.

EduSystems
15
20 25 . 30 40 50
5 10
x

x
x

Table 1-3.

BASIC Functions and Arithmetic Operations
EduSystems
5 ]0 15 20 25 30 40 50

Functions

Description

SQR(x)
SIN(x)
COS(x)
TAN (x)

Square root of x(vx)
Sine of x (x in radians)
Cosine of x (x in radians)
Tangent of x (x in
radians)
Arctangent of x (x in
radians; result in radians)
eX (e=2.712818)
Natural log of x (lo~x)
Absolute value of x (Ixl)
Greatest integer of x
Sign of x (+ 1 if positive,
-1 if negativc, 0 if zero)
Random number betwecn 0 and 1
Truncates decimal portion of x
Controls printing head
position on Teletype
Converts character code
to character. Used only
with PRINT statement.

ATN(x)
EXP(x)
LOG (x)
ABS(x)
INT(x)
SGN(x)
RND(x)
FIX(x)
TAB (x)
CHR$(x)

1-144

x
x
x
x

x x

x
x
x
x
x

x x

x
x
x
x

Table 1-3 (Cont.)
Functions

BASIC Functions and Arithmetic Operations
EduSystems
5 10 15 20 25 30 40 50

Description

MID(A$,M,N) Returns N characters,
starting at the Mth character of A$.
LEN(A$)
Returns the number of
characters in A$.
CAT(A$,B$)
Returns a string of A$
concatenated with B$
(maximum of 6 characters returned).
Arithmetic Operations
SYMBOLS
t exponentiation
* multiplication
I division
+ addition
subtraction
ORDER OF EXECUTION
1. Parenthetical expressions
2. Exponentiation
3. Multiplication and Division
4. Addition "and Subtraction

1-145

x
x

1-146

2
edusystems
INTRODUCTION
EduSystem 5 is a BASIC-speaking supercalculator--calculator
because it can be used like a calculator to obtain fast, accurate
results, super because it is a computer that ·'uses BASIC and does
much more than calculate. EduSystem 5 has the ability to operate
in two modes: immediate and programmable. Immediate mode
allows the user to perform arithmetic calculations and obtain immediate results without writing programs. The problem and the
solution are printed at the Teletype to provide a hard copy for
future reference. In programmable mode, one uses BASIC to
write programs and type them on the Teletype keyboard. Programs
are stored in computer memory and can be printed via the teletype
and, if desired, punched on paper tape to be used again in the
future.
EduSystem 5 BASIC contains all the elements needed to write
and execute meaningful programs. In addition, it provides several
special features.

• Several commands may be typed on a single line. PrograIll;s
using this feature require less storage in the computer, thus
enabling users to write longer programs.
• A colon (:) may be used in place of the PRINT command
to save time and storage space.
• Typing errors are easily corrected with the use of the ALT
MODE (or ESCAPE), ~ back arrow, or RUB OUT key.
• INPUT statement responses may be either mathematical
expressions or numeric values.
All these features, and more, are yours with EduSystem 5. And
it expands. If your needs grow beyond EduSystem 5, you can
expand it, with a few simple additions, to an intermediate-scale
EduSystem 15.
2-1

System Components
EduSystem 5 is composed of a table-top computer (PDP-8/F)
with 4096 words of core memory and a Teletype with paper tape
reader and punch. An optional off-Jine Teletype with paper tape
reader and punch allows users to prepare paper .tapes of their
programs before coming to the EduSystem 5 and increases the
number of persons who may use it each day. Each EduSystem 5
includes the BASIC language processor, a user's guide, and a
self-teaching workbook for ·learning the BASIC language.
System Expansion
.
EduSystem 5 is easily expanded to EduSystem 15 by adding a
DECtape magnetic tape drive (TD8-E), memory extension control,
256 word read-only memory, and an EduSystem 15 software kit.
(See Chapter 4 for a full description of the capabilities of EduSystem 15.)
BASIC LANGUAGE CAPABILITIES
EduSystem 5 BASIC includes the language elements shown in
Table 2-1. These elements are used as explained in Chapter -1.
Differences jn usage for EduSystem 5 are discussed below.
Line Numbers
In EduSystem 5 BASIC there is no upper limit on the size of
the line number for any statement.
Single-Character PRINT Command
EduSystem 5 permits the use of a colon (:) in place of the
PRINT command. This abbreviation can be used in place
of PRINT in either programmable or immediate mode. The statement format is the same as that of the PRINT command, for
example:

1eJ

: 5+ 10 :is the same as 10

PR I NT 5+ 10

Multiple Statements per Line
EduSystem 5 allows more than one command to
single line. Commands after the first begin with
character ("), typed as SHIFTIL on the keyboard.
often more. understandable when statements, such
2-2

be
a
A
as

typed on a
back slash
program is
a series of

LET's!, are grouped into a single line. For example, tbe program:

A= 1\ 8= 4 \ C= 6

: (A+B )*C

END

is the same as

10
20
32J

LET A= 1
LET 8=4
LET C=6

PRI NT (A+8)*C

END

and will produce the same result when the RUN command
typed:

RUN
30

This capability is helpful when the program to be written is too
big for EduSystem 5. Commands take less storage in the computer
when they are grouped as a single statement.
Immediate Mode
EduSystem 5 allows certain BASIC statements to be used in
immediate mode, that' is, to be issued and ,executed immediately
without being included in a formal program. Commands commonly
used with immediate mode are PRINT, (or:), LET; FOR, and
NEXT. Immediate mode is a quick way to calculate expressions
and equations. For example, the statement
:SIN(l),COS(l),TAN(l)

followed by the RETURN key, causes the sine, cosine, and tangent
of 1 radian to be printed immediately, as follows:
0.841471

0.540302

1.55741

Typing multiple commands per line is especially useful in the
immediate mode. A table of square roots of the .first 10 integers
lRemember that the word LET is optional in the LET statement.

2-3

could, for example, be generated by typing the following single
line and pressing the RETURN key:

FOR 1:1 TO 10\: SQRCI),\NEXT I
1

2.44946

1.41421
2.64575

1.73205
2.82843

2
3

2.23607
3.16228

Although they are rarely used, other BASIC commands are
available in immediate mode. The immediate GOTO command
may be used to start a program at a point other than the beginning.
This is accomplished by loading the program into the computer
memory and typing, for example:
GO TO 200

After the RETURN key is pressed, the program execution will
begin automatically at line number 200. In this case, the RUN
command need not be typed.
INPUT Statement
EduSystem 5 allows the student to respond to the INPUT query
(?) with either a mathematical expression or :a numeric value. An
e~pression entered as input may contain one or more arithmetic
operations and may use any available BASIC function. For example, the BASIC statement:
10

INPUT X

could be answered in any of the following ways:
? 10 t5+6

1SQR(4f2-2)

1LOG(186) ,

As explained in Chapter 1, the INPUT statement may have
multiple inputs. These inputs may be either mathematical expressions or numeric values. For example, the BASIC statement
10

INPUT A,B,C

could be answered as follows:
1512,INT(876.33),7+6t25

2-4

NOTE
Remember that you use CTRL/C to stop
a program that is running.
PROGRAM EDITING
There are two times when a program may require editing ·pro:cedures. The first occurs while a line is being typed but before
the RETURN key has been pressed. The second occurs when a
line has been completely typed and the RETURN key has been
pressed. Each situation has its own editing procedures.
Procedure 1: Before the RETURN key is pressed.
Three keys may be used to correct typing ~rrors: ALT MODE
(or ESCAPE), ~ (back arrow), or RUBOUT.
\,

ALT MODE (or ESCAPE) is used to delete an entire line.
When this key is used, BASIC prints $DELETED, erases
that line from the program, and returns the carriage so that
line may be retyped.
~

(back arrow), SHIFTjO on the keyboard, or RUB OUT is
u'sed to delete a character from a line. BASIC prints a back
arrow, deleting the last character from that line. More than
one back arrow deletes more than one character, in reverse
.order.
Procedure 2: After the RETURN key is pressed.
Once aline of the program has been transmitted to computer
memory via the RETURN key, several methods of correction may
be. used. Lines may be inserted, deleted, or changed.
INSERTION: To add a line to a program, assign, a line
number that falls between two existing lines, type the line
number and text, and press RETURN.
DELETION: To erase a line from computer memory, type
the line number only and press the RETURN key.
CHANGE: To change an individual line, simply retype it.
The old instruction is replaced by the new one.
ERROR MESSAGES
EduSystem 5 checks all commands before executing them. If it
cannot execute a command, it informs the user by printing one'

2-5

of the following messages arid the line number in which the error
was found,
Message

Explanation

SYNTAX ERROR

Command does not have correct syntax.
Common examples of syntax errors are
misspelled commands, unmatched parentheses, and other typographical errors.
The function used was deleted at system
load time and thus is not available. A
DEF statement will produce this message
if the DEF capability was deleted.
Program and variables exceed computer
capacity. Reducing one or the other may
help. If the program has undergone extensive revision, try punching it out, typing SCR, and reloading.
The subscript used is otltside the DIM
statement limits.
A branch statement (GOTO, GOSUB,
or IF) references a nonexistent line.
FOR loops are too deeply nested.
FOR and NEXT statements are improperly paired.
Subroutines are too deeply nested.
GOSUB and RETURN statements are
improperly paired.
No more items are in the data list.
A function has been given an illegal argument, e.g., SQR(-l).

FUNCTION ERROR

TOO-BIG ERROR

SUBSCRIPT ERROR
LINENO ERROR
FOR ERROR
NEXT ERROR
GOSUBERROR
RETURN ERROR
DATA ERROR
ARGUMENT ERROR

To correct the error indicated by the message, the appropriate
line in the program must be corrected in the manner described
under Program Editing, Procedure 2.
OPERATING INSTRUCTIONS
Initial Installation
When EduSystem 5 is first installed, it must be loaded with a
special software program, the BASIC language processor. Once
this software is loaded, it need not be reloaded. Perform the
following steps to load BASIC.
1. Plug the EduSystem 5 computer into a standard 3-prong

2-6

electrical outlet. Plug the Teletype into a second standard
outlet. Turn the key lock on the front of the computer to the
power position and turn the Teletype to line. Set all switches
on the SWITCH REGISTER (to the left of the ADDR
LOAD switch) to the "down" position and press the EXTD
ADDR LOAD switch.
2. Perform the following set of switch manipulations. In each
step, there are 12 figures which correspond to the 12 switches
labeled SWITCH REGISTER (SR) on the front of the computer. The
symbol indicates that the corresponding switch
should be set to its "up" position. The 9 symboi means that
the corresponding switch should be set to its "down" position. The octal instructions which correspond to this diagram
OCTAL
appear on the right.2

*9999 9"
9??' 9"
?M .?*
999 ?"
99. 99'9
999 999
*9* 99*

Set SR to: . . . . . .
Set SR to:
Set SR to:
Set SR to:
Set SR to:

_9
-9
*?
"9

Set SR t o : ' "
Set SR t o : ' "

999
Set SR to: "9999
Set SR to: .9* 9__
Set SR to: . . 9 999
Set SR to:
*99
Set SR t o : ' "

Set SR to:
SetSRto:
Set SR to:

999
9"
_9
9*.
9*9

*-9" ... ...

6032

99* then lift DEP
... then lift DEP
"9 then lift DEP
"9 then lift DEP
"9 then lift DEP
999 thenliftDEP

6031
5357
6036
7106
7006
7510

then lift DEP

5357

-9 then lift DEP
99* then lift DEP
... 'then lift DEP
* 99 then lift DEP
999 then lift DEP
**9 then lift DEP

7006

?"
...
_9
*9* 9" *\2* "9
9**

then pressADDR LOAD 7756
then lift DEP

.9- 9" .9_ ...

SetSRto: . . .
Set SR to:

"?
9*9

6031
5367
6034
7420
3776

thenliftDEP

3376

then lift DEP
and again lift DEP

5356

2The octal instructions are provided for those familiar with the octal, or
base 8, number system. An explanation of this system is included in
Introduction to Programming 1972.

3. Place the tape labeled EDUSYSTEM-5 in the Teletype paper
tape reader. Position the tape at the: single row of holes
punched at the beginnXl;f the tape.
4. Set the SR to . . .
(7756); then press
ADDR LOAD. Press the CLEAR switch, then the CONT
switch. Push the paper tape reader switch to the START
position. The tape should read in. If it stops before the end
of tape, an error has occurred. Repeat steps 2, 3, and 4.
5. When the tape has read in properly, BASIC prints the
following message:
SEL·ECT THE SMALLEST SET OF FUNCTIONS NEEDED FROM THE
FOLLOWING CHOICES
AT N
I IXI I I I I I
LOG+EXP
I IXIXI I I I I
SIN+COS+TAN I tXIXIXI I ! I
DEF(FN)
I IXIXIXIXI I I
SQR
I IXIXIXIXIXI I
RND
I IXIXIXIXIXIXI

.9."IN THEN 90
60 PRI NT
10 PRINT "O.K. IT'S YOUR CHOICE."
80 STOP
90 PR INT
100 PRINT "y OR N7";
110 GOTO 30
120 END

RUN NH
\~OULD YOU LIKE TO DO THIS AGAIN , <=, >=). Relational operators may only be used
in IF statements'.

S1
S2

Statement as a whole is not properly written and, as a
result, does not conform to proper BASIC syntax. For
example, a semicolon is allowed in a PRINT statement
but not in a READ or INPUT statement.
4-14

Message

Explanation

Statement's command word is not one of the BASIC
statement types.

The program is too large to be run. Cause is usually an
extremely large number of PRINT -statements.

Program is either too large or too complex to be run.
The total number of variables, constants, functions, and
line numbers should be reduc~d, if possible.

A OOSUB, OOTO, or IF statement contains a line
number which does not exist.

A quotation mark indicating the beginning of a string of
text does not have a corresponding quotation mark at
the end of the text string.

Program Logic Errors 4
Some errors do not show up until the program is actually executed. An example of this type of error is an expression which
uses a square root of a variable. If, when this square root is actually calculated, the variable has a negative value, a program
logic error has occurred. EduSystem 15 prints the following messages if _program logic errors occur.
Message

Explanation

A CHAIN statement tried to chain to a program which
was not available in the DECtape storage area.

Program ran too long and was automatically stopped by
the system.

The program ran out of data. It attempted to do a
READ after all data had been read.

4Some program logic errors may be corrected by the method described
under Program Editing, Procedure 2. Most, however, necessitate the rewriting of the program.

4-15

Messag~

Explanation

The program attempted to divide by zero. Instead of
dividing by zero, BASIC divides by the smallest possible
number, giving a result of about 10500 • This error does
not cause the program to stop.

An expression contains a function which was not defined
in a DEF statement.

The program is too complex to be executed. The problem is generally that too many subroutines have the!Dselves executed GOSUB instructions.

Programl.ttempted to take the logarithm of a negative
number
zero.

A RETURN statement was used outside of a subroutine
or a subroutine was entered by at GOTO instead of a
GOSUB.

See GS.

Program attempted to take the square root of a negative
number. BASIC automatically takes the square root of
the absolute value of the number instead. This error
does not cause the program to stop .

Program used a subscript which was too large for the
variable. The maximum size of a subscript is specified
in a DIM statement.

There is no more room on the DECtape to write data.
The program attempted to do a WRITE statement when
the data list was full. (Note that if this error occurs, the
program text will no longer be intact. A NEW, OLD,
or ~CR command must be used to clear the program
area.)

OPERATING INSTRUCTIONS
Loading the System
When EduSystem 15 is first installed, it must be loaded with a
special software program, the BASIC language processor. Once this
4-16

software has been loaded, it need not be reloaded. Perform the following steps to load BASIC.
INITIALIZE THE DECTAPE UNIT
Perform the following steps to prepare the TD8E DECtape unit
for software loading.
'
1. Set the REMOTE/OFF/LOCAL switch to OFF.
2. Place a DECtape on the left spindle with the DECtape
label out.
3. Wind four turns of tape onto the right spindle.
4. Set the REMOTE/OFF/LOCAL switch to LOCAL.
S. Wind a few turns of tape onto the right spindle with the ~
switch to ensure that the tape is properly mounted.
6. Dial 0 on the unit selector dial.
7. Set the REMOTE/OFF/LOCAL switch to REMOTE.
8. Set the WRITE ENABLE/WRITE LOCK switch to
WRITE ENABLE.
INITIALIZE COMPUTER MEMORY
To initialize the PDP-8/F memory, perform the following steps.
1. Turn the key lock on the front of the computer to
POWER.
2. Perform the following set of switch manipulations on the
SWITCH REGISTER (to the left of the ADDR LOAD
switch). In each step, there are 12 figures which correspond to the 12 switches labeled SWITCH REGISTER
(SR) on the front of the computer. The • symbol indicates that the corresponding switch should be set to its
"up" position. The :: /
~-

~ lr;t~ T

vb (s \ evllow&b) cry 0.. G~ X b]

~c..~

ptQAfifJ'"\

I4t
JUvl.,
ulitllJ<..
IILtft b)I
SireJ
IF THEN Statement
The IF THEN statement described in Chapter 1 is used to transfer conditionally from the normal order of program execution. For
example:

X>Y THEN 200

transfers control to ]ine 200 if X is greater than Y. If X is not
greater than Y, control transfers to the line following line 50. EduSystem 20 BASIC uses the IF THEN statement in this way to
change the order of program execution. It also allows the IF THEN
statement to, conditionally perform an operation without changing
the order of program execution. For example:

X>Y THEN PRINT "X>Y"

If X is greater than Y, BASIC prints X> Y. Whether or not X

is greater than Y, the next statement executed is the one following
line 50. IF THEN used in this manner does not change the order
of program execution.
5-8

The IF THEN statement can also be used to transfer control to
a subroutine. For example:

25 I If' A+B=C THEN. GOSUB 100

If A
100.

equals C, control is transferred to the subroutine at line

Truncation Function (FIX)
EduSystem 20 BASIC includes all the functions discussed in
Chapter 1 (see Table 5-2). In addition, it includes the truncation
function (FIX) which returns the integer part of x. For example:
PRI FIXC-842.756)
-842

Notice that FIX is like INT for positive arguments. In fact, FIX
could be defined as:
f/J /}

lIu

FIX(X)==SGN(X)*INT (ABS(X» _

.-+.:-:- _//

ac~~. ~ dtfoitd~ <1~ f!ht UJai::~} ~:V·Lf~

fJr

CHR$ Function !,..''-IT 4Ak'~fv.1;D VA ~
I X . JD Wlt tit. .
Occasionally, it is desir-~l~ to type a character other than the
printing ASCII set (see Appendix B) or to convert ASCII character codes t? their respective characters. A special PRINT statement function, CHR$, is used for this purpose: This function
takes as its argument a single constant or variable and prints the
single character whose character code corresponds to that value.
For example:
10 FOR 1=0 TO 9
20 PRINT CHRS(I+48)J
30 NEXT I
RUN
0123456789
READY

/It ~S()
"IN,) ur Clf'R.- 'Ii'(J l{)<,
J' ~ MA l(\f?~

.. ~~ ~ -tiM w etvui tfO

~J ~~-rA1?

.
LA/'

This program prints "0123456789" because 48 to 57 are the
ASCII values for the characters 0 through 9. The following special characters can also be printed using the CHR$ function:

rtD PR iAJ7

('NUL L (/ 5-9fke GH1(~· C2-5 ~)

............

Bell
Line feed
Carriage return
Quote (")
Back arrow (~)
Form feed

CHR$(7)
CHR$(10)
CHR$(13)
CHR$(34)
CHR$(95)
CHR$(12)

For each ASCII character there is a second acceptable form of
CHR$ function. The second code is obtained by adding 128 to the
ASCII code given in Appendix B. For example, both CHR$(65)
and CHR$(193) cause the character A to be output.
ON·GOTO Statemenl

The ON-OOTO statement permits the program to transfer control to one of a set of lines depending on the value of a formula.
The statement is of the form:
line number ON formula OOTO line number, line number . ..

The formula is evaluated and then truncated to an integer. This
integer is used as an index to tell which of the line numbers receives control. If the integer is 1, the first line number is used; if it
is 2, then the second is used; etc. Obviously, the formula after
truncation cannot be zero or negative or greater than the number
of line numbers in the list. For example:
10 ON A+2 GOTO 100,200,300,400

If A is 2, then control is passed to line 400. The range A can have
in this example is -1 to 2.

ON GOSUB Statement

The OOSUB and RETURN statements are used to allow the
user to transfer control to a subroutine and return from that subroutine to the normal course of program execution (see Chapter 1).
The ON GOSUB statement is used in the same manner as the ON
OOTO statement described previously. The statement is of the
form:
'
line number ON formula OOSUB line number, line number . ..

5-10

The formula is evaluated and then truncated to an integer. Depending on the value of the integer, control is transferred to the
subroutine which begins at one of the line numbers listed. When
the RETURN statement is encountered, control transfers to the
line following the ON GOSUB line. For example:
50 ON X GOSUB 200,300,400
If X is 1, 2, or 3) control will transfer to line 200, 300, or 400
re:;pectively. If X is not equal to 1, 2, or 3, line 50 is ignored .9

7 fLAA i? 1
HAVE A HIGH SPEED PUNCH {Y OR N)?Y
HAVE A HIGH SPEED READeR (Y OR 1'J)7Y'
ABOVE CORRECT (Y OR N)?Y

If the number of users is more than 1, BASIC continues the dialog
by asking:
PDP-8/L COMPUTER ?

When all responses have been entered, BASIC asks:
IS THE ABOVE CORRECT

V\A)"\L \ i~~

v{ ",-v..{\-t~l

_~A

QGAt ~~'
,J

',J

As explained in Chapter 1, the INPUT statement may have
multiple inputs. These inputs may be either mathematical expressions or numeric values. For example, the statement:
10 INPUT AlBIC

could be answered as follows:
148148'SISQR(48)

Comments
Previously, the use of the REMARK (or REM) statement to
introduce a comment on a single line was discussed. Comments
may also be appended to any line by starting the comment with a
single apostrophe ('). All characters typed after the apostrophe
are ignored when the program is executed. For example:
10 LET X=4 'SET X TO ITS INITIAL VALUE
20 GOTO 1~ 'LOOP BACK TO START

6-4

When responding to an INPUT statement, the user may add a
comment which prints on the terminal but has no effect on the
running program. For example:
UJ INPUT X
20 PRINT X
RUN
.
? 2 'LET X BE 2

READY
.'~

IF THEN Statement
The IF THEN statem~nt described in Chapter 1 is used to transfer conditionally from the normal ?rder of program execution. For
example:
25 IF A<-B THEN 100

transfers control to line 100 if A is less than or equal to B. If A
is greater than B, control transfers to the line following line 25 ..
BASIC-E uses the IF THEN statement in this way to change the
order of program execution. It also allows THEN to be followed
by an executable BASIC statement. This statement is executed
onl if the IF relation is true; otherwise control passes to the next
separate statement. or example:
50 IF 2+2=4 THEN LET A=7'PRINT A

Since the statement (2+2=4) is true, BASIC prints 7. The next
. statement executed is the one following line 50. IF THEN used
in this manner does not change the order of program execution.
The IF THEN statement can also be used to transfer control to
a subroutine. For example:
25 IFA+B=C THEN GOSUB 100

If A+B equals C, control is transferred to the subroutine at line

100. Otherwise, the next statement executed is the one following
line 25.
'
6-5

ON-GOTO Statement
The ON-GOTO statement permits the program to transfer
control to one of a set of lines depending on the value of a formula.
The statement is of the form:

line number ON formula GOTO line number,line number . ..

The formula is evaluated and then truncated to an integer. This
integer is used as an index to tell which of the line numbers receives control. If the integer value of the formula, is 1, the first
line number is used; if the value is 2, then the second is used; etc.
Obviously, the formula after truncation cannot be zero or negative
or greater than the number of line numbers in the list. For example:

If X is 2, then control passes to line 400. The allowable range of
X in this example is -1 to 2, so that the range of the formula

value is 1 to 4.
ON GOSUB Statement
The GOSUB and RETURN statements are used to allow the
user to transfer control to a subroutine and return from that subroutine to the normal course of program execution (see Chapter 1).
The ON GOSUB statement is used in' the same manner as the
ON GOTO statement described previously. TlJ.e stateme~!_ i~of",
the form: -

line number ON formula GOSUB line number, line number . ..

If X is 1, 2, or 3, control transfers to line 200, 300, or 400, respectively. If X is not equal to 1,2, or 3, line 50 is ignored.

6-6

RANDOMIZE Statement
The random number (RND) function produces a random number between 0 and 1, as described in Chapter 1. A given program
using the RND function produces the same random numbers each
time it is run. If the user wants the random number generator to
calculate different random numbers every time the program is run,
EduSystem 25 BASIC provides the RANDOMIZE statement.
RANDOMIZE is normally· placed at the beginning of a program
which uses the RND fmiction. When the program is executed,
RANDOMIZE causes the RND function to choose a random starting value so that the same program gives different results each
time it is run. For example:
10 RANDOMIZE
20 PRINT RND(0)

prints a different number each time it is run. For this reason, it is
good practice to debug (detect, locate, and correct mistakes) a
program completely before inserting the RANDOMIZE sta~ement.
To demonstrate the effect of the RANDOMIZE statement on
two runs of the same program, the RANDOMIZE statement was
inserted as line 15 below:
15 RANDOM
20 FOR 1=1 TO 5
25 PRINT "VALUE" I "IS" RND(0 )
30 NEXT I
RUN
VALUE 1 IS .3808637
VALUE 2 IS .7119271
VALUE 3 IS .9687586
VALUE 4 IS .03029916
VALUE 5 IS .4629068
READY
RUN
VALUE
VALUE
VALUE
VALUE
VALUE

2
3
4
5

IS
IS
IS
IS
IS

.8916059
.2441537
.3154383
.07033823
.583024

READY

6-7

Truncation Function (FIX)
EduSystem 25 BASIC includes all the functions discussed in
Chapter I (sce Table 6-2). In addition, EduSystem 25 includes the
truncation function (FIX) which returns the integer part of the
function argument. For example:
PRI FIX(82+100.677S,
182

PRJ FIX(SQR(85.54621»
9

Notice that FIX is like INT for positive arguments. In fact, FIX
could be defined as:
FIX(X)=SGN(X) *INT(ABS(X))

EXTENDED SYSTEM CAPABILITIES
In addition to the BASIC language features previously discussed, EduSystem 25 has several extended features that allow the
user to write longer, more complex programs. These features include the ability to store programs on DECtape, create and manipulate data files on DECtape, and link program segments together
to al10w longer user programs. Another extended capability allows
character strings to be input, manipulated, compared, and output.
These extended features are discussed below.
String Variables
EduSystem 25 BASIC has the ability to manipulate alphanumeric information (commonly called strings). A string is a
sequence of six or fewer printing ASCII characters (see Appendix
B). If a string contains more than six characters, only the first six
are retained. A string variable is signified by one letter followed
by the dol1ar sign ($) character and, optionally, by one or two
subscripts. The following are all acceptable string variables:
A$
B$(l)
C$(2,5)
READING STRING DATA
Strings of characters may be read into string variables from
DATA statements. Each string data element is composed of one
to six characters enclosed in quotation marks. The quotation marks
are not part of the actual strings. For example:

"'~.~~.
~

\JZ.o.t ~ \o.P~ ~ '~Lt 6-~ E:~t-

d. OJ'..fA,

f; ~ ,

}..fA }/'f.

s-tr.)

Rtp,.{)kf

10 READ AS,SS,CS
20 DATA "JONES","SMITH","TAYLOR"

The string JONES is read into A$, SMITH into B$, and TAYLOR
into C$. If the string contains more than six characters, excess
characters are ignored.
PRINTING STRINGS
The normal PRINT statement may be used to print string information. If a semicolon is used to separate string variables in a
PRINT command, the strings are printed with no intervening
spaces. For example, the program:
10 READ AS,SS,CS
20 PRINT CSJSS'AS
30 DATA ttlNG" ,·"SHAR", ttT IME-"
.-/
RUN
.
'~Z:"""
'-

causes the following to print :

10 READ AS,BS,CS
20 PRINT CSJBSAS DELETED

10 READ AS, Bslcs
20 PRINT CSJBSICS DELETED

--~

READY

INPUTTING STRINGS
String information may be .entered into a BASIC program by
means of the INPUT command. Strings typed at the keyboard
may contain any of the standard BASIC characters except back
arrow (~) and quotation mark. Back arrow, as always, is used to
delete the last character typed. Commas ar~ used to separate string
variables, as with numeric data. If a string contains a. comma, the
entire string must be enclosed in quotation marks. The following .
program demonstrates string input:
10 INPUT AS,BS,CS
20 PRINT AS,BS,CS
RUN
1 JONES,SMITH,TAYLOR
JONES
SMITH

TAYLOR

READY

6-9

Strings and numeric information may be combined in the same
INPUT statement as in the following example. Note that if an
input string contains more than six characters, only the first six are
retained.
10 INPUT AIASIB$
20 PRINT ASIBS1A
RUN
? 01754IMAYNARDIMASS.
MAYNAR
MASS.

1754

READY
co,) I lie: ,

The numeric variable A is set to 1754 (leading zeroes are not
printed). The string MAYNAR is put in the string variable A$,
and the string MASS. is put into the string variable B$.
LINE INPUT
Strings of more than six characters may be entered by means of
the LINPUT (line input) statement. A LINPUT statement is followed by one non-subscripted variable, e.g., A$. The following
program illustrates the use of the LINPUT statement:
10 LINPUT AS
20 Z=-AS(0)
30 FOR I-I TO INTCZ/6+.9)
40 PRINT ASCI);
50 NEXT 1
60 PRINT
RUN
? MAYNARDI MASS.
01754
MAYNARDI MASS. 01754
READY

This program inputs the entire line of type from the terminal and
stores the characters so that the values of the string variables are,
effectively:
A$(1) = MAYNAR
A$(2)
D, MAS

A$(3)=S. 01
A$(4) = 754
A$ (0) = total number of characters stored
Commas and quotation marks are treated as ordinary characters
and, hence, are stored in the string variables. LINPUT accepts a
line of characters up to a carriage return.
6-10

WORKING WITH STRINGS
Strings may be used in both LET and IF THEN statements. For
example:
10 LET YS="YES"
20 IF B$, >=, <=, <> are used with string
variables to represent alphabetic order; they could be used to alphabetize a list of strings .. The arithmetic operations (+, -, *, /, t)
are not defined for strings. Thus, statements such as LET A$ = 3 *5
and LET C$ = A$+ B$ have no meaning and should never be used
in a BASIC program. Such statements do not cause an error message to be printed; however, the results of such operations are
undefined.
'
STRING FUNCTIONS
EduSystem 25 'BASIC contains several functions for use with
character strings. These functions allow the program to access part
of a string (MID), generate a numeric string or value (CRR$),
determine the number of characters in a string (LEN), and link
two strings together ( CAT) .

)

CHR$ Function
Occasionally, it is desirable' to type a character other than the
printing ASCII set (see Appendix B) or to convert ASCII character 'codes to their respective characters. A special PRINT statement function, CRR$, is used for this purpose. This function
takes as its argument a single constant or variable and prints the
single character whose character code corresponds to that value.
6-11

1" FOR 1=" TO 9
2" PRINT CHRS(I+46);
30 NEXT I
RUN
0123456769
READY

This program, prints "0123456789" because 48 to 57 are the ASCII
values for the characters 0 through 9. The following special characters can also be printed using the CHR$ function:
CHR$(7)
CHR$(10)
CHR$(13)
CHR$(34)
CHR$(95)
CHR$(12)

Bell
Line feed
Carriage return
Quote (")
Back arrow (~)
Form feed

For each ASCII character there is a second acceptable form of
CHR$ function. The second code is obtained by adding 128 to the
ASCII code given in Appendix B. For example, both CHR$« 65)
and CHR$ (193) cause the character A to be output.
MID Function
The MID function is used to obtain a portion of a character
string. The format of this function is:
MID(A$,M,N)
BASIC accesses the characters in the string variable A$ and
returns N characters, beginning with position M. Characters in a
string are numbered 1 through 6. Consider the following example:

10 LET AS·"UVWXYZ"

20 PRINT MID(AS,3,3)
RUN
WXY
READY

6-12

LEN Function
The LEN function returns the number of characters in the string
argument. Characters in a string are numbered 0 thro'ugh 6. For
example:
10 RS.tfRANDOM"
20 PRINT LEN(RS)
RUN
6

READY

CAT Function
The CAT function returns a string of characters which are the
result of the concatenation (1i~king) of two other character strings.
A maximum of six characters can be returned by the CAT function; if the first string to be linked contains six characters, only
those six characters are returned. For example:
10 AS."01234S"\BS="678910"
20 PRINT CAT(ASIBS)
RUN
01234S
READY.
"-

If the first string contains less than six characters, they are linked

as shown in the following program.
10 A$="EDU"\B$="-2S"
20 PRINT CAT(A$IBS)
\ RUN
EDU-2S
READY

Program. Storage / Retrieval
EduSystem 25 allows the system DECtape to be used for permanent on-line program storage. Programs stored in this way may
be loaded instantly without handling a paper tape or typing a
lengthy program.
STORING USER PROGRAMS
User written programs may be stored on DECtape. Each program to be saved must have an assigned name, entered at the beginning of the programming session. The NEW command is given
to clear any existing program and define the name of the new program to be entered. To use the NEW command, the user types:
6-13

NEW

and presses RETURN. The system then asks for:
NAME--

The user then types any name of 1 to 6 characters (the first ·of
which must be alphabetic) and presses RETURN. BASIC assigns
that name to the program to be entered. The user may change the
name of the program at any time by typing the RENAME command. BASIC again asks for NAME- and assigns the new name
to the program being entered. RENAME does not delete the existing program as does NEW.
Once a program has been named and typed correctly, it may be
stored on DECtape with the SAVE command. Any existing program stored under the same name is deleted when a SAVE command is issued. Thus all stored programs have unique names which
may be used to recall them in the future. To store a program, the
user, having named and entered a program, types:
SAVE

and presses RETURN. BASIC stores the program on DECtape
under the name specified with an extension identifying the user
terminal from which the program was saved. For example, a program named ALPHA that is saved from ter'minal .E2 (see Starting
EduSystem 25) is stored as ALPHA .E2. Extensions protect the
programs from access by other terminals, i.e., terminal .E1 cannot access a program stored by terminal .E2.
When the program has been stored, BASIC prints READY. At
this time, the program still resides in computer memory; storing·
does not erase computer memory. A NEW or SCR command must
be typed to erase the program from memory after it has been
stored on DECtape.
RETRIEVING USER PROGRAMS
User programs stored on DECtape are brought into memory
with the OLD command. Only programs stored from the same
user terminal can be retrieved at that terminal. When recalling a
program with the OLD command, the user must give exactly the
6-14

same name as was used 'when the program was stored. To use the
OLD command, the user types:
OLD

and presses the RETURN key. The system then asks for NAME-.
The user can also use the OLD command and the program name
(e.g., ALPHA) on the same line as follows:
OLD ALPHA

BASIC brings the stored program into memory but does not
erase the program from DECtape. If the user wishes to modify the
program, he can make the necessary modifications, then issue another SAVE command. This procedure replaces the original stored
program on DEC tape with the modified version of the same name.
The user can obtain a listing of all programs stored from his
terminal by using the CATALOG command. CATALOG, like
all other program storage/retrieval commands, is an immediate
command. It is used by typing CATALOG and pressing RETURN. BASIC immediately prints a listing, without extensions,
of all programs stored by the terminal from which the CATALOG
command was issued.
RUNNING VERY LONG PROGRAMS
EduSystem 25 accommodates BASIC programs up to 250 lines
long. If a program is any longer, it may be necessary to break it
into several segments. A program that has been broken into more
than one piece is called a chained program.
Each part of a chained program is saved on DECtape as a separate program, complete with name and system-assigned extension.
The last statement of each part to be executed is- a CHAIN statement specifying the name of the next 'section of the program. For
example, a program named ALPHA is segmented into three parts:
ALPHA, BETA, and GAMMA. ALPHA is loaded with the OLD
command.
250 CHAIN "BETA"

6-15

The last statement in ALPHA is a CHAIN statement.
or
250 CHAIN

The string variable (B$) may be used if the segment name was
previously assigned to it, for example:
248 BS="BETA"

When this CHAIN statement is reached, the BET A segment of the
program is loaded and executed. The BET A segment then chains
to the next (GAMMA) segment of the program with a statement
such as:
399 CHAIN "GAMMA"

Each separate part of the program links automatically to the next
part of the program.
The CHAIN command may also be used to branch to a stored
program -from a working program. For example:
10 INPUT "WHAT LESSON DO YOU WANT" A$
20 CHAIN A$

RUN
WHAT LESSON DO YOU WANT? DELTA

would cause BASIC to retrieve, load, and execute the program
named DELTA.
DELETING STORED PROGRAMS
The UNSAVE command is used to delete a program already
stored. UNSAVE must either be preceded by a NEW, OLD, or
RENAME command which specifies the name of the program to
be deleted or the command must be typed as:
UNSAVE ALPHA

specifying the name (e.g., ALPHA) of the program, on DECtape,
to be deleted. The user must use exactly the same name used when
6-16

the program was stored. Only programs which were saved from
the terminal being used may' be deleted by a user at that terminal,
e.g., a user at terminal .Bl may delete only those programs stored
with an extension of .El. (These are programs listed in response
to the CATALOG command.)
USING PUBLIC LIBRARY PROGRAMS
Programs stored by' the System Manager with the extension
.EB may be accessed by all users. These programs are collectively
called the public library. To obtain a listing of the available public
library programs, the user types:
CATS

and presses the RETURN key. A listing of the public library programs is printed. A sample listing is shown below:

ROCKET
LUNAR
POLUTE
ELECT
SNOOPY
GAMBLE
READY

The user can access any program in the public library by typing
OLD$ and the desired program name. For example, the user types:
OLOS SNOOPY

The library program SNOOPY is loaded into memory and the
system prints READY. The user can then execute SNOOPY by
typing RUN or, if desired, can obtain a listing of SNOOPY by
typing LIST. User may access the public library but cannot SAVE
or UNSAVE the library programs. These programs are protected
by the .EB extension.
The user can also access public library programs by chaining to
them from a program. For example, the _user can access the public
6-17

Iibraryprogram ELECT by including the following statement in his
program:
55 CHAINS f9ELECT"

, or by including the following statements:
50 ES."ELECT"
55 CHAINS ES

Data File Storage1Retrievai
Just as some programs may be too large to be executed as a
single p.rogram, other programs may need to store and use more
data than may be contained in DATA statements within the program. If this is the case, data may be stored on DECtape. Data
stored in this way is called a data file.
EduSystem 25 allows users to read and write OECtape data
files. These data files may contain numeric or string data. Data files
are the perfect way to test student programs. The instructor may
create a data file which all student programs must use and then
answers may be stored in another file which may be checked
automatically.
Data files are stored automatically by EduSystem 25 on the
DEC tape mounted on DECtape drive 1. Data files are stored with
an extension similar in principle to that previously discussed for
programs. Terminal .El data files have the extension .Dl, .E2
data files use .D2, etc. The system manager's extension (.ES)
uses .DS data files. Normally, .DS files can only be read; users
are limited to reading only by placing DECtape drive 1 on WRITE
LOCK.
CREATING DATA FILES
When the user desires to store data on DECtape, he must create
a data file, or use an existing data file. Data files are created with
the OPEN FOR OUTPUT command. For example, the user wishes
to create a data file named DATAI0 (date file names, like program file names, can be 1 to 6 characters long, the first character
of which must be alphabetic). The data file name can be used in
the OPEN statement or a string variable can represent it. A data
6-1S

file would be created when the following statement was executed
In a program:
10 OPEN "DATA10" FOR OUTPUTI12

The data file name must be enclosed in quotation marks. This statement could also be coded as:
10 OPEN AS FOR OUTPUTI12

if A$ has been set equal to DAT Al O. The 12 at the end of the
statement indicates that 12 blocks are to be reserved for this file.
Any number of blocks up to 64 may be reserved in this manner.
If no blocks are res~fved in the OPEN FOR OUTPUT statement,
the system assumes that the file is to be 10 blocks long.
When the data file has been created, or reopened, the user may
write data into the file with the PRINT # statement. This statement may contain either numeric or string data separated by
commas or semicolons. For example, a single data item can be
entered by typing the following:

20 PRINT

248

This statement writes 248 and a carriage return/line feed onto a
data file that has been opened for output. Several data items may
be included in a PRINT # statement, with commas printed as
separators between data items on each line of the output file. The
commas must be enclosed in quotation marks to have them print
on the output file. For example:

writes each of the above items on the data file as separate data
items as follows: 1, 2, 3, 4, 5 and a carriage return/line feed
exactly as the items would be input from the terminal.
6-19

Character strings are used in the PRINT # statement in the
same manner, for example:
25 A$="JONES"\8$="SMITH"\C$="TAYLOR"
30 PRINT#IA$IB$IC$

would write three separate character strings onto the DECtape as
follows: JONES, SMITH, TAYLOR and a carriage return/line
feed. Writing PRINT # statements with multiple operands (data jtems) saves space on the DECtape data file because fewer carriage return/line feeds need to be stored.
When al1 data has been entered with PRINT # statements, the
output file should be closed with the CLOSE statement. Since
EduSystem 25 allows only one output file to be opened at a time,
the CLOSE statement is used to close the output file. For example:
3~

READING DATA FILES
When the user wishes to usc data stored on DECtape data files,
he opens a previously created file with the OPEN FOR INPUT
statement. If, for example, the user wishes to read data stored in
a file named DATAlO, he can reference this name in the OPEN
statement or use a string variable t<;> represent. it. The data file
would be opened when the following statement was executed in
a program:
40 OPEN

"DATf\l~"

FOR INPUT

The data file name must be enclosed in quotation marks. The above
statement could also be coded as:
35 BS="DATA10"
40 OPEN BS FOR INPUT

When the data file has been opened for input, the user may read
data from the file with the INPUT # statement. The INPUT #
statement searches the file for a carriage return/line feed character and inputs the next data item, or items. This statement may
contain either alphabetic or string variables separated by commas
or semicolons. For example, the statement:

6-20

searches for a carriage return/line feed character and inputs the
next five separate data items· (separated by either a comma, a
semicolon, or a carriage return/line feed ) from a data file.
The following program uses the examples in this section to
demonstrate data file usage:
10 X$="DATA10"
15 OPEN X$ FOR

OUTPUT~12

-20 PRINT*~1~2~3~4~5
, 25 A$="JONES"'B$="SMITH"'C$="TAYLOR"
30 PRINT#~A$~H$IC$
35 CLOSE
40 OPEN X$ FOR INPUT
50
55

INPUT#~A~H~C~D~E
INPUT#~A$~B$~C$

PRINT
65 PRINT
70 PRINT
75 PRINT
60

A~H~C~D~E
A$~B$~C$

RUN
1

JONES

SMITH

TAYLOR

LISTING· DAT A FILES
The user can obtain a listing of the data files for his terminal
by typing the FILELOG command. This immediate mode command is typed as:
FILELOG

or
FIL

and produces a listing of the data file names without extensions.
For example:
FILELOG
DATAl'"
NUMBER
CIRCLE
TIMER
READY

6-21

ERASING DATA FILES
Data files can be deleted from DECtape with the KILL command. If, for example, the user wishes to erase a file named
DATAIO, he types:
KILL DATA lei

when the RETURN key is pressed, BASIC deletes DATAIO from
the data file and prints READY. The KILL command and the file
name must be separated by a space. This command deletes only
those data files entered from the same terminal, i.e., with the same
extension.
USING PUBLIC DATA FILES
Data files stored by the System Manager with the extension .08
may be accessed by all users. To obtain a listing of the available
public data files, the user types:
FILELOGS
FILS

and presses the RETURN key. A listing of the public data files· is
printed. A sample listing is shown below:
FILS
TESTell
TESTI1J2
DATASI1J
DATASS
DATA611J

The user can use the data in any public data file by opening the
file for input. For example, to use the data in a public file named
DATA55, the user types:
911J OPENS "DATASS" FOR INPUT

Included in a program, the above statement would make the data
in DATA55 available to the user program. The user can manipulate this data in his program but cannot change the data file in any
way. Public data files are protected by the .08 extension.
6-22

Table 6-1.

EduSystem 25 BASIC Statement Summary

Command (Abbreviation)

Explanation

Input/Output Statements
. LET

Assign a value to a variable.
The word LET is optional.
READ(REA)
'j
Assign values from data list to
variables.
.PRINT(PRI)
Print out the indicated information on the Teletype.
DATA(DAT)
Provide data for a program.
RESTORE(RES)
Restore the data list.
INPUT(INP)
Get values or expressions from
the Teletype.
LINPUT(LIN)
Get long character string from
the Teletype.
'GOTO(GOT)
Change order or program execution.
'IF THEN(IF THE)
Conditionally perform speci,,:
fied operation or conditionally
change order of program execution.
Set up a program loop .
. FOR TO STEP(FOR TO STE)
'NEXT(NEX)
End of program loop.
GOSUB(GOS)
Go to a subroutine.
RETURN(RET)
Return from a subroutine.
, Conditionally change order of
ON GOTO(ON GOT)
program execution according
to evaluation of formula contained in statement.
ON GOSUB(ON GOS)
Conditional1y go to a subroutine according to evaluation of
formula contained in statement.
Insert a program comment.
'REMARK(REM or ')
Cause RND function to ranRANDOMIZE(RAN or RANDOM) domly select new sequence of
random numbers between 0
and 1.
Define a function.
DEF FN
Stop program execution.
STOP (STO)
End a program (not required
END
with EduSystem 25).
Editing/Control Commands.
LIST(LIS)
LIST n(LIS n)

List entire program in memory.
List line n.

6-23

Table 6-1 (Cont.).

EduSystem 2S BASIC Statement Summary

Command (Abbreviation)

Explanation

'. LIST n,m(LIS n,m)

List lines n through m inclusive.
Delete line n.
Delete lines n through m inclusive.
Search line n for the character
typed.
Return to KEY (normal) mode.
Execute the current program.
Erase the current program
from memory.
Same as SCRATCH.
Read a program from the Teletype paper tape reader or
punch a program on the Teletype paper tape punch.
Stop a running program, print
STOP, and then READY.

DELETE n(DEL n)
DELETE n,m(DEL n,m)
EDIT n(EDI n)
KEY
RUN
'SCRATCH(SCR)
BYE
TAPE(TAP)

,CTRL/C

Program Storage/Retrieval Commands
'NEW
Clear memory, request program
name.
'RENAME(REN)
Chan&e the name of the program currently in core memory.
Store program in memory on
'SAVE
DECtape, using the name specified by NEW, RENAME, or
OLD and an extension determined by the user's terminal.
Erase memory, retrieve, load
CHAIN A$
and begin execution of the
stored program named in A$.
Used to segment a large program into workable sections~
Chain to public library proCHAIN$ A$
grams.
Clear memory, request pro'OLD
gram name, bring named program to memory from DECtape.
Delete from DECtape the proVNSAVE
gram named in most recent

6-24

Table 6-1 (Cont.).

EduSystem 25 BASIC Statement Summary

Command (Abbreviation)

Explanation
NEW, RENAME, or OLD
command.
List names of stored programs
for this user (extensions are
not printed).
List public library programs.
Request public library program
name, bring named program to
memory from DECtape.

'CATALOG(CAT)
'CAT$
'OLD$

Data File Commands
OPEN A$ FOR OUTPUT,X

OPEN B$ FOR INPUT
.-;()
OPENS B$ FOR INPUT
INPUT #

PRINT #
CLOSE
FILELOG(FIL)
FILELOG$(FIL$)
KILL A$

6-25

Create a DECtape file named
by A$, If the file already exists on DECtape, this command
reopens it. X determines the
number of blocks reserved for
this file. It may be any integer
up to 64. If no X is entered,
lOis assumed.
Open the existing file named
by B$. If no such file exists, '
an error ~ssage is printed.
Open a· .EOJfile named by A$.
Read variables (numeric and/
or string) from the input file
previously opened.
Write data (numeric and/
or string) onto the output file
previously opened.
Close open output file.
Catalog the data files stored by
this user (used only in immediate mode).
Catalog the data files stored by
the System Manager with the
extension ,DO.
Delete a DECtape data file
named by A$.

Table 6-2.

EduSystem 25 BASIC Function Summary

Function

Description

"ABS(X)
ATN(X)
COS(X)
EXP(X)
INT(X)
LOG (X)
RND(X)
'SGN(X)
SIN(X)
'SQR(X)
TAN (X)
TAB (X)
FIX (X)
CHR$(X)
MID(A$,M,N)
LEN(A$)
CAT(A$,B$)

Absolute value of x.
Arctangent of x(result in radians).
Cosine of x(x in radians).
eX (e=2.718282).
Greatest integer of x.
Natural logarithm of x.
Random number.
Sign of x (+ 1 if positive, -1 if negative, 0 if zero).
Sine of x (x in radians) .
Square root of x.
Tangent of x (x in radians) .
Controls printing head position on Teletype.
Truncates decimal portion of x.
Converts character code to character. Used only
with the PRINT command.
Returns N characters, starting at the Mth character of A$.
Returns the number of characters in A$.
Returns a string of A$ concatenated with B$
(maximum of 6 characters returned).

ERROR MESSAGES
EduSystem 25 checks all statements and commands before executing them. If a statement or command cannot be executed, the
system informs the user by printing an error message and the line
number (if available) in which the error was found (see Table
6-3 ). Procedures used to correct errors are described under Program Editing.
Table 6-3.

EduSystem 25 Error Messages

Message
WHAT?
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR

1
2
3
4
5
6
7

Explanation
Immediate mode statement or command not understood. It does not begin with a line number and is
not a valid system command.
Log of negative or zero number was requested.
Square root of negative number was requested.
Division by zero was requested.
Overflow, exponent greater than approximately +38.
Underflow, exponent less than approximately-38.
Line too long or program too big.
Characters are being typed too fast; use TAPE command for reading paper tapes.

6-26

Table 6·3 (Cont.).

EduSystem 25 Error Messages

Message
ERROR 8
ERROR ~
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR

10
11
12
13
14
15

ERROR
ERROR
ERROR
ERROR

16
17
18
19

ERROR 20
ERROR 21
ERROR 22
ERROR 23
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR

24
25
26
27
28
29
30
31
32
33
34
35
36
37
38

ERROR
ERROR
ERROR
ERROR

39
40
41
42

Explanation
System overload caused character to be lost.
Program too complex or too many variables.
(GOSUB, FOR, or user defined function calls are too
deeply nested.)
Missing or illegal operand or double operators.
Missing operator before a left parenthesis.
Missing or illegal number.
Too many digits in number.
No DEF for function call.
Missing or mismatched parentheses or illegal dummy
variable in DEF.
Wrong number of arguments in DEF call.
Illegal character in DEF expression.
Missing or illegal variable.
Single and double subscripted variables with the same
name.
Subscript out of range.
No left parenthesis in. function.
Illegal user defined function, not FN followed by a
letter and a left parenthesis.
Mismatched parentheses or missing operator after
right parenthesis.
Syntax error in GOTO.
Syntax error in RESTORE.
Syntax error in GOSUB.
Syntax error in ON.
Index error out of range in ON.
Syntax error in RETURN.
RETURN without GOSUB.
Missing left parenthesis in TAB function.
Syntax error in PRINT.
Writing past end-of-file.
Missing or illegal line number.
Attempt to GOTO or GOSUB to a nonexistent line.
Missing or illegal relation in IF.
Syntax error in IF.
Missing equal sign or improper variable left of the
equal sign in LET or FOR.
Subscripted index in FOR.
Syntax error in FOR.
FOR without NEXT.
Syntax error in LET.

6-27

Table 6-3 (Cont.).

EduSystem 25 Error Messages

Message
ERROR 43
ERROR 44
ERROR 45
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR

46
47
48
49
50
51

ERROR
ERROR
ERROR
ERROR
ERROR

52
53
54
55
56

Explanation
Syntax error in NEXT.
NEXT without FOR.
Too much data typed or illegal character in DATA
or the data typed in.
Illegal character or function in INPUT or READ.
Out of data.
Unrecognized command: RUN mode.
Bad file name or file not found.
Syntax error in LINPUT.
String error, argument is incorrect type or out of
bounds.
String function error, missing or illegal argument.
File not open or bad syntax after #.
Reading past end of file.
Bad syntax in OPEN.
No room for file on DECtape.

PROGRAM EDITING
There are two times when a program may require editing procedures. The first occurs while a line is being typed but before
the RETURN key is pressed. The second occurs when a line has
been completely typed and the RETURN key has been pressed.
Each situation has its own editing procedures.
Situation 1: Before the RETURN key is pressed.
Three keys may be used to correct typing errors:
RUBOUT, or ALT MODE (or ESC).
~

(SHIFT /0),

(back arrow), SHIFT/O on the keyboard, or RUBOUT
is used to delete a character from a line. BASIC prints the
back arrow, deleting the last character from that line. More
than one back arrow deletes more than one character, in
reverse order.
ALT MODE (ESC on some Teletypes) is used to delete an
entire line. When this key is used, BASIC prints $DELETED,
erases that line from the program, and returns the carriage
so that the line may be retyped.
6-28

Situation 2: After the RETURN key is pressed.
Once a line of the program has beer.t transmitted to computer
memory via the RETURN key, several methods of correction may
be used. Lines may be inserted, deleted, or changed.
INSERTION
To add a line to a program, assign a line number that falls between two existing lines, type the-line number and text, and press .
RETURN.
DELETION
To erase a line from computer memory, type the line number
only and press the RETURN key. The DELETE command may
also be used to erase lines' from memory. To erase a single line,
type DELETE and the line number and press RETURN. DELETE followed by the two line numbers separated by a comma
erases all lines between and including the two given. For example:
DELETE 10,,20
erase~

lines 10 through 20.

CHANGE
Old instructions may be replaced by new ones by retyping the
line. This procedure is adequate for changing simple lines. When,
however, the line contains a complex formula or a long message to
be printed, it may be changed with the EDIT command. The EDIT
command allows the user to access a single line and search for
the character or characters to be changed. To use this command,
type
EDIT line number
and press the RETURN key. BASIC waits for a search character
to be typed (BASIC docs not print this search character when it
is typed). This search character is one that already exists on the
line to be changed. After the ,search character is typed, BASIC
prints the contents of that line until the search character is printed.
At this point, printing stops and the user has the following options:
• Type new characters; BASIC inserts them following the
ones already printed.
• Type a form feed (CTRL/L) to cause the search to proceed to the next occurrence, if any, of the search character.
6-29

• Type a BELL (CTRL/G) to signal a ~hange of search
character, then type a new search character.
• Use the RUBOUT or ~ key to delete one character to the
left each time the key is pressed.
• Type the RETURN key to terminate editing of the line at
that point, deleting any existing text to the right.
• Type the ALT MODE key to delete all existing characters
to the left except the line number.
• Type the LINE FEED key to terminate editing of the line,
saving all the remaining characters on that line.
When the EDIT operation is complete, BASIC prints READY.
Note that line numbers cannot be changed with the EDIT command. The following example demonstrates the EDIT command.
An incorrect line was typed and entered to the system as follows:
60 PRINT "PI=3.14146

ABOU~'"

The line was edited as follows:

EDIT 60
PRINT .. PI=3.14146 .... S9 ABOUI"T'"

First 6 was entered as the search character. BASIC printed the
line to the 6, and the RUBOUT key was typed twice to remove the
two incorrect digits (46) and 59 was inserted in the line. CTRL/G
was typed and another search character (%) was entered. BASIC
printed characters to the % which was removed with a RUB OUT
and replaced with aT. The LINE FEED key was typed to terminate the edit and save the remaining characters. If the line is
listed, the following'is printed on the Teletype.
LIST 60
60 PRINT "PI=3.141S9 ABOUT'"
READY

6-30

OPERATING INSTRUCTIONS
Loading EduSystem 25

EduSystem 25· software is supplied on a DECtape. This tape,
called the system DECtape t must be used to create the system
when the system is installed. Perform the following procedures to
activate EduSystem 25.
'
INITIALIZE THE DECT APE UNIT
Perform the following steps to prepare the DECtape unit for
loading software:
1. Set the WRITE ENABLE/WRITE LOCK switch to
.WRITE LOCK.
2. Set the REMOTE/OFF/LOCAL switch to OFF.
3. Place the system DECtape on the left spindle with the
DECtape label out.
4. Wind four turns of tape onto the right spindle.
5. Set the REMOTE/OFF/LOCAL switch to LOCAL.
6. Wind a few turns of tape onto the right spindle with the
~ switch to ensure that the tape is properly mounted.
7. Dial 0 on the unit selector dial.
8. Set the REMOTE/OFF/LOCAL switch to REMOTE.
INITIALIZE COMPUTER MEMORY
The system may be activated in one of two ways: with an automatic loader (hardware bootstrap) or with an OS/8 bootstrap
loader. The following instructions are for an EduSystem- 25 that
includes a hardware bootstrap. If the EduSystem does not have a
hardware bootstrap, see Introduction to Programming'1972, Chapter 9, for OS;8 bootstrap loading instructions.
1. Turn the key lock on the computer console to POWER.
2. Turn all Teletypes to LINE.
3. Mount the EduSystem 25 system DECtape on drive 0 as
described above.
4. Set the SWITCH REGISTER (SR) to 0600 (octal).4
5. Press and raise the HALT switch.
6. Press and raise the SW switch.
The EduSystem-25 DECtape spins and the system indicates that
it is active by printing a period (.) on the console Teletype. If the
4

An explanation of the octal, or base 8, number system is included in Introduction to Programming 1972.

6-31

system is not CJctivated, ensure that the correct DEC tape is being
used and repeat the above procedures.
Immediately following the period printed by the system, the
user enters the characters shown below:
.R EDU25

The period is printed by the OS/8 Keyboard Monitor. The user
types R to request the running of a program, in this case, EduSystem 25.r. When the RETURN key is pressed, the system prints:
TO BOOTSTRAP HACK OS/8 MONITOR:
LOAD ADDRESS 07600
AND START

This message means that EduSystem 25 (or other OS/8 programs)
can be started by setting the SR to 7600 and pressing ADDR
LOAD, CLEAR, and CONT. The OS/8 Monitor prints another
period, to allow the user to request a program. If, for example,
the user types an incorrect response to the ensuing system dialog,
. he can restart the dialog by reloading (bootstrapping back) the
OS/8 Monitor from location 7600 and again requesting that EduSystem 25 be run.·
ANSWER SYSTEM DIALOG
When the system has been activated correctly, it prints the identification message:
EUUSYSTEM 25

HASIC

and begins to ask certain questions which the user must answer
to establish the system configtlration. The first question is:
NUMBER OF USERS (l TO 5)7

The user responds with a single digit from 1 to 5, depending on the
number of terminals to be used. If one user is specified, this ques-

[) Refer to Introduction to Programming 1972, Chapter 9, for a complete
explanation of the OS/8 Operating System.

6-32

tion ends the initial BASIC dialog. If more than one user is indicated, BASIC continues the dialog by asking:
PDP-B/L COMPUTER (Y OR N>?

The user responds Y if the EduSystem 25 computer is a PDP-8/L,
N if not. An N response to this question prompts the next question:
STANDARD REMOTE TELETYPE CODES (Y OR N)?

BASIC is asking for a PT08 or KL8E device code for each Teletype to be used (excluding the console Teletype). Standard PT08
·or KL8E device codes arc 40, 42, 44, 46, 50, 52, and 54. When
a system using PT08 or KL8E interface units i~ first installed, the
user determines the specific device code for each Teletype and
labels each Teletype with its specific device code. If device codes
are standard, the user responds Y to this question and BASIC
assumes the standard device codes and continues the dialog. If
device codes are not standard, the user enters N; BASIC then asks:

TELETYPE 11 DEVICE CODE?

BASIC asks this question for each Teletype to be used, up to
seven times for a~ 8-user system. The user responds with the specific 2-digit device code for each Teletype.
When the device codes have been determined, or if the computer
is a PDP-8/L, BASIC asks the following question:
SAME AMOUNT OF STORAGE FtiR ALL USERS?

The '!bove question requires the user to decide whether to partition
the available core equally among the users on the EduSystem 25.
(Since EduSystem 25 software 'uses 4K of core, the available core
is always 4K less than the total core on the system.) If the user
responds Y to this question, BASIC determines the size of the core
memory available and divides it equally among the users, then ends
the dialog. If Nis the response, BASIC determines the amount of
available core storage and prints the highest core field according
to the following:

6-33

Field 7-32K core memory
Field 6-28K; core memory
Field 5-24K core memory
Field 4-20K core memory
Field 3-16K core memory
Field 2-12K core memory
Field 1- 8K core memory
. For explanation purposes, the following dialog is written for a
16K, 5-user EduSystem 25. The available core is to be allocated as
follows:
User 1-10 blocks (user 1 is the console terminal)
. User 2-- 6 blocks
User 3-- 8 blocks
User 4-- 4 blocks
User 5-- 4 blocks
Each core field contains 16 blocks; a core field may be divided
among several users, but no user may be allotted blocks in more
than one core field. To determine the number of blocks, BASIC
prints the following dialog and the user answers as shown:
FIELD
THERE
YOUR
THERE
YOUR
FIELD
THERE
YOUR
THERE
YOUR
THERE
YOUR

3
ARE 16 BLOCKS LEFT IN THIS FIELD.
ALLOCAT IUN FOR USER !If I WILL 91=: nU!,.' l'IAI\IY HLUCKS? 19.1
ARE 06 BLOCKS LEFT IN THIS FIELD.
ALLOCAT 10111 FOR USER *2 1" ILL BE HOW MANY BLOCKS? 6
2

ARE 16 BLOCKS LEFT IN THIS FIELD.
ALLOCATION FOR USER '3 WILL BE HOW MANY BLOCKS?8
ARE 08 BLUCKS LEFT IN THIS FIELD.
ALLOCATION FOR USER #4 WILL BE HUW .MANY' BLOCKS?4
ARE ~4 BLOCKS LEFT IN THIS FIELD.
ALLOCATION FOR USER *5 WILL BE HUW MANY BLOCKS?4

When an invalid response is made to any of BASIC's questions,
an error message is printed and the question is repeated. For
example:
STANDARD REMOTE TELETYPE CODES B.
Repeated uses of RND in a program return different values between zero and one. The sequence of numbers is, however, the same
each time the program is run. Thus, the sequence is reproducible
for later checking of the program. The RANDOMIZE statement
allows the user to make the random number sequence returned by
the RND function different each time a program is run. That is,
when executed, the RANDOMIZE statement causes the RND
function to select randomly a new sequence of random numbers. If
RANDOMIZE is used, it normally appears as one of the first lines
in a program.
Running Long Programs
EduSystem 30 runs programs of up to 6000 characters in interactive mode and up to 5000 characters in batch mode. These
limits correspond to roughly 2.00' and 250 lines per program,
respectively. In some cases, interactive programs which are at or
near the 6000 character limit and which contain many complex
FOR, IF, and GOSUB sections are too large to be run. If this is
the case, the NOLINE command may be used to gain more space.
If NOLINE is used, program logic errors· which are detected
while the program is executing cause an error message to be
printed, but the line number of the error is not printed. NO LINE
allows substantially longer programs to be run.
If the program to be run is substantially longer than the 6000character limit,. it may still be run by means of a technique known
as chaining. The program is written in sections, each of which is

7-5

less than 6000 characters. A chained program may have many of
these program sections and, hence, may be indefinitely long. Each
section of the total program is then stored in the system storage
area with the SAVE command under a separate name. The final
command to be executed in all but the last section is a CHAIN
statement containing the name of the next section of the program.
For example, the statement

950 CHAIN "PART10"

would cause the system to load and execute the stored program
whose name is PARTIO.
In the CHAIN statement, the name of the next section of the
program must be encoded in quotation marks and must be
exactly six characters long. If the actual naml~ of the next section
is less than six characters, one or more spaces must be inserted
before the second quotation mark to make a total of six characters.
For example, if the next section of the program is named LINK2,
the following CHAIN statement would be used:

955 CHAIN "LINK2"

Execution of the CHAIN statement loads and executes the
named program. The previous section of the program is deleted.
Thus, the uSer only needs to load the first section and run it. All
succeeding .sections of the chained program load and execute
automatically.
Using a Data File
Just as some programs may be too large to be executed in one
piece, other programs may need to store and use more data than
may be accommodated under normal system operation. If this is
the case, data may be temporarily stored in the system storage
area. Data stored in this way is referred to as a data file.
7-6

The data file is actually a part of the program data which is de- .
fined by a DATA statement. All data within a program is gathered
from the DATA statements into a data list which is then read by
READ statements. As items are read from the list, they are marked
as already having been used. A READ statement always fetches
the next item from the list. In fact, the data list may be considered to have a movable marker which remembers the next item
of the list. The marker initially marks the first data item. As READ
statements are executed, the marker moves down the list. A RESTORE statement moves the marker back to the top of the list.
The data file capability allows a' program, by means of a
WRITE statement, to change and add to this data list as well as
to read it. The WRITE statement format is the same as the DATA
statement format. Writing a variable puts the value of that variable
in the next place in the data list. The data item that was there previously is replaced by the new value. If a WRITE statement follows a RESTORE, it changes the first item or items in the data
list. If it follows one or more READs (or WRITEs), the WRITE
statement changes data items further down in the data list. The
total number of items' which may be put in the data list depends
on the size of the program. Maximum sized BASIC programs
may have up to 1000 items; small programs have room for 2000
items.
Programs which write data on the data list must keep track of
how much data has been' written and the order in which it was
output. If data which has been written is to be subsequently read,
a RESTORE statement must be executed to return the marker
to the top of the data list. If data has been written off the end of
the data list, the program must remember how many items the data
list c~i1tains, and be careful not to try to READ more data items
than are there. The normal BASIC check for end of data does not
exist for a written data list. The program must also be sure that
it does not write more data. than the data list can contain (10002000 items). Writing too much data causes part of the user's
BASIC program to be destroyed.
Data files are frequently used in conjunction with chaining
since data written onto the data list by one program section may
be read by the next section. The program section which writes the
7-7

data must execute a RESTORE just before the CHAIN statement. The next section, which reads the data list, must not have
any DATA statements since this data would destroy the data
items written by the previous section.

Character Variables and String Capability
Standard BASIC statements deal only with numbers, assuming
all variables to be decimal values. However, BASIC is also capable of performing many useful operations on characters or words
(strings of characters) instead of numbers. The character handling
capabilities of BASIC depend on the representation of individual
characters as numbers. Each character has its own numeric code
(or character code), as indicated in Appendix B. When a character
is input, by an INPUT statement, it is converted to a numeric
code. All internal processing of that character uses this code. Since
the code is a number. it can be used and manipulated' with any
BASIC statement. When a user program is to output a character,
BASIC converts the numeric code back into a character and
prints the character. In short, characters stored in a BASIC program are indistinguishable from numeric values: The only difference is in the way they are used, i.e., that certain numeric values
actually represent characters.
The INPUT statement is used to input characters. A dollar sign
($) is placed before a variable name to indicate that a character
code is to be input rather than a decimal number, e.g., INPUT $A.
When the character is typed, its character code is stored in the
indicated variable. It is important not to confuse character input
with numeric input. A potential confusion lies in the fact that the
numeric values are themselves characters. For example, the value
234 is composed of the three characters 2, 3, and 4. If these three
characters were input to a BASIC program as character variables,
they would be' entered as three separate numeric (character code)
values rather than as the single value 234. Whether the input
is character code or numeric, the physical characters typed at the
terminal are identical; the difference is entirely in the way that the
program interprets the input. In the following examples, each
program executes an INPUT statement. In the program on the
left, three characters are entered and three variables are set up. In
the example on the right, a single numeric value is input.
7-8

10 PRINT "ENTER VALUE";
20 INPUT X
30 PRINT X
40 END
RUN NH

10 PRINT "ENTER VALUE ";
20 INPUT $Xll$X21$X3
30 PRINT.Xl;X2JX3
40 END
RUN NH
ENTER VALUE 234 50

ENTER VALUE?234
234

READY
READY

Note that character INPUT statements do not cause a question mark to be printed. Therefore, a series of characters may be
typed without intervening question marks. Programs doing character input must therefore indicate, by PRINT statements, when
input is expected. Also note that the $ is not part of the variable
name. It is used only in INPUT statements to indicate that typed
characters are to be converted to their numeric character codes
before being stored in the variable.
Character codes may be converted to their respective characters
by means of the special PRINT statement function CHR$. CHR$
is the inverse of the dollar sign INPUT convention. The CRR$
function takes, as its argument, a single constant or variable and
prints the single character whose code corresponds to that value.
For example:
50 PRINT ChR$(65)

prints the character A. CHR$. may only be used in PRINT
statements.
One of· the most frequent uses of the character capability is to
enter words or characters into BASIC programs in response to
questions. For example, a program might ask the user if he wants
to run the program again with a different set of input data. The
user responds by typing Y if he wants to run again or by typing N
if not. The program then compares the code of the character' entered with the character code of Y to determine if they are equal.
If so, it branches back to the beginning of the program. If not, the
program executes the remaining statements. The following program
illustrates the use of character variables in making a run-time
decision.
7-9

10 PRINT

PRINT "WOULD YOU LIKE TO DO THIS AGAIN (Y OR N)1";
INPUT SA
40 IF A=#Y THEN l~
5~ IF A<>#N THEN 9~
60 PRINT
70 PRINT "O.K. IT'S YOUR CHOICE."
8~ STOP
90 PRINT
1~0 PRINT "Y OR N1"';
110 GOTO 3~
120 END·
RUN NH
2~
3~

WOULD YOU LIKE TO DO THIS AGAIN *5\END

is the same as
10 LET A=3
20 LET B=8

30 LET C=13
40 PRINT (A+B+C>*5
50 END

and will produce the same result when the RUN command
typed:."

RUN NH
120

READY

This multiple-statement capability is helpful when writing long programs since statements require less storage in the computer when
they are grouped as a single statement.
Listing the Program
The LIST command may be used to list all or part of the current
program. LIST print'S the program statements in their proper order,
regardless of the order in which they were entered. The 'EduSystem
30 LIST command has four different forms, as shown below.
7-12

Command
LIST
LIST n

LISTNH
LISTNHn

Meaning
List the entire program. Precede it by a header line 3
giving the name of the progran:t.
List the program starting at the given line number
(n). Precede it by a header line. The line number
must be separated from LIST by two spaces.
List the entire program, but do not print a header
line.
List the program starting at the given line number
(n), but do not print a header line.

NOTE
The programmer may stop a listing at any
time by typing CTRLjC on the keyboard.
Executing the Program
The programmer may execute a program at any time by typing
the ,RUN command. The existing program is inspected for errors;
if none exist, it is executed. If an error is detected, an error message (see the section on Error Messages) is printed. In either case,
at the end of the run, BASIC prints READY, indicating that the
program may now be changed or rerun. There are two types of
RUN. commands: RUN and RUN NH. RUN executes the current
program, preceding it by a header line. RUN NH (NH means no
header) executes the current program but does not print a header
line. RUN and NH must be separated by a single space. The user
may terminate program execution at any time by typing CTRLjC.
Loading a Card Program for Interactive Use
Programs previously written on cards may be loaded for use in
interactive mode. The progr~p1 'Cleck is pr;e~eded by a NEW card
and followed by a KEY c,artl. The ,U:~er mounts this deck in the
Executing Card Programs for
card reader in the normal'way
instructions) and types the BA H command. Cards are processed
in normal batch fashion u
the KEY card is read. The KEY
card switches the system, interactive mode. The program is then
available for execution J;. editing from the interactive terminal.
j/O

3 A header line consists of the program name followed, on the same line,
by the system name (EDU BASIC). If no prograin name was assigned,
the system prints "*NONE* EDU BASIC".

7-13

After two RUN commands (or after some number of RUNs if the
privileged BATCH command is used), the system automatically
returns to processing any additional card program in the reader.

Storing Programs on Paper Tape
Once a program has been entered or read correctly, it may be
saved on paper tape for quick reloading, as follows:
1. Turn the Teletype control knob to LINE.
2. Type LISTNH but do not press the RETURN key.
3. Turn the Teletype paper tape punch ON.
4. Press SHIFT /CTRL, type "PPPPPP" to produce some
leader tape.
5. Press the RETURN key.
6. When punching is complete, press SHIFT /CTRL, type
"PPPPPP" to produce some trailer tape.
7. Turn the Teletype punch OFF.
8. Carefully rip tape off punch. Notice that an arrow head is
at the beginning of the program and an arrow tail a't the
end.
Reloading Programs From Paper Tape
Programs punched on paper tape may be reloaded using the
Teletype (TTY) paper tape reader. The TAPE command is used
to load programs from paper tape as follows:
1. Insert the paper tape in the TTY reader, with the arrow
head facing out of the reader.
2. Turn the TTY control knob to LINE.
3. Type NEW, then press the RETURN key.
4. Type the program name.
5. Type TAPE, press the RETURN key.
6. Turn the TTY paper tape reader to ST ART.
7. When the tape has read in, turn the TTY reader to FREE.
Remove the paper tape.
A special control command, ECHO, may be used with TAPE
to prevent the program from being listed while it is being read. The
first time it is used, ECHO inhibits all printout. A second ECHO
command restores normal printout.
Privileged C.ontrol Commands
Several optional commands are available which modify and control a program run. All· of these commands are considered to be

7-14

privileged in the sense that their use is restricted. The privileged
commands are available only if the privileged command capability
was selected when EduSystem 30 was loaded. During normal system operation these commands are disabled. If' a user attempts to
use a privileged command, it is ignored and the system prints
WHAT?
A special command, the PRIVILEGE command, is used to make
these privileged commands available. To use PRIVILEGE, the
user types PRIVILEGE and the RETURN key. The system then
waits for the user to type a one to six character password code.
(The typed characters are not printed.) At the time the system was
loaded, a password was typed into the system. The characters typed
after the PRIVILEGE command are compared to this password.
If they match, the PRIVILEGE command is successful and all
privileged commands may then be used. If they do not match, the
message INVALID PASSWORD is printed and all privileged commands continue to be unavailable.
In short, the user must know the password in order to use any
privileged command. It is' important that the password be kept
secret. For this reason, the password is never printed when the user
types it. It is possible to change the password code at any time. The
command, PASSWORD, which. changes the code is, of course, a
privileged instruction. Certain privileged commands are used only
when processing card programs; these commands are discussed
under Executing Card Programs. The other privileged commands,
SAVE and UNSAVE, are discussed below. All privileged commands must be typed at the terminal; they cannot be entered on'
cards.
Using the System Storage Capability
EduSystem 30 allows the system device (DECdisk or DECtape)
to be used for permanent on-line storage of programs. Programs
stored in this way may be loaded instantly, without the need to load
a paper tape or card deck or type a program.
SAVE AND UNSAVE COMMANDS'
Two commands, SAVE and UNSAVE, may be used to change
the contents of the system storage area. Because the amount of storage space is limited, and to prevent accidental erasure of stored
7-15

programs, both SAVE and UN SAVE are privileged commands.
During normal system operation they are disabled. SAVE and UNSAVE may only be used after a successful PRIVILEGE command
has been executed.
The SAVE command stores the programs currently in memory
on the system storage area (DECtape or DECdisk) and gives it the
name specified by the last NEW, OLD, or NAME command. Any
existing program stored under this name is deleted. Thus, all stored
programs have names which may be used to recall th,em in the future. If a SAVE is attempted when the privileged commands are
disabled, the system prints WHAT? and ignores the command. If
a S'Uccessful PRIVILEGE command has been executed, but the
storage area is full, the message NO SPACE is printed and the
program is not stored.
The UNSAVE command is used to delete a program already
stored. UNSAVE must be preceded by a NEW, OLD, or NAME
command which specifies the name of the file to be deleted. The
user must be certain to use exactly the same program name as he
used when be first identified the program. Like SAVE, UNSAVE
is ignored unless preceded by a successful PRIV ILEGE command.
If the program to be deleted does not exist in the system storage
area, the message FILE NOT SAVED is printed and no program
is deleted.
CATALOG COMMAND
The CATALOG command may be used to obtain a list of the
names of all programs available in the system storage area. The
CATALOG list includes the number of storage blocks used by the
program. A standard EduSystem 30 includes 116 blocks of storage
space (for nonstandard systems, see Calculating Available Storage). The CATALOG command may be used to determine how
many of these blocks have been used and, hence, how many are
free.
LENGTH COMMAND
If the system storage space is almost full and another program is
to be saved, the LENGTH command may be used to determine if
there is room to store the current program. If space is not available,
an existing· program must be deleted. In all cases, the maximum
number of stored programs, regardless of size or storage device,
is 62.
7-16

OLD COMMAND
The user may load programs stored in the system storage area at
any time by typing the OLD command. After the OLD command
is entered, the system prints OLD PROGRAM NAME. The user
then types the name of the program to be loaded. The user must
be certain to use exactly the same program name as he used when
he first identified the program.
Returning to Batch Mode

At the end of an inte.ractive session, the system is ready for
further batch processing. When the system prints READY, the
BATCH or STACK command may be used to begin a batch run.
Program Editing

There are two times when a program may require editing procedures. The first occurs while a lirie is being typed but before the
_ RETURN key is pressed. The second occurs when a line has been
completely typed and the RETURN key has been pressed. Each
situation has its own editing procedures.
Procedure 1 : Before the RETURN key is pressed.
Three keys may be used to correct typing errors: ALT MODE
(or ESCAPE), -E- (back arrow), or RUBOUT~
ALT MODE (or ESCAPE) is used to delete an entire line.
When this key is used,BASIC prints DELETED, erases that
line from the program, and returns the carriage so that the
line may be retyped.
-E- (back arrow), SHIFT /0 on the lceyboard, or RUBOUT is
used to delete a character from a line. BASIC prints the back
arrow, deleting the last character from that line. More than
one back arrow deletes more than one character, in reverse
order.
Procedure 2: After .the RETURN key is pressed.
Once a line of the program has been transmitted to computer
memory via the RETURN key, several methods of correction may
be used. Lines may be i~serted, deleted, changed, or renumbered.
INSERTION: To add a line to a program, assign a line number that falls between two existing lines" type the line number
and text, and press RETURN.
7-17

DELETION: To erase a line from computer memory, type
the line number only and press the RETURN key.
CHANGE: To change an individual line, simply retype it.
The old instruction is replaced by the new one.
RENUMBER: Occasionally, repeated editing and insertions
result in there being no more room in an area of a program
to insert new lines. It is then necessary to spread out the line
numbers so there is room for new ins~rtions. The RESEQUENCE command is used for this purpose. To renumber a
program, type the RESEQUENCE command. This command
changes the first line's number to 100 and renumbers each
succeeding line wjth an increment of 10. RESEQUENCE also
automatically changes all GOTO, GOSUB, and IF statements
to correspond to the new line numbers.
WRITING AND RUNNING CARD PROGRAMS
·W:riting a ]~r()gram on Cards
Programs to be submitted to Edu~ stem 30 are first transcribed
onto specially formatted BASIC carl s. These cards are preprinted
with a series of small rectangular b xes. Each card has 39 columns
of boxes, with the column num r printed along the lower edge.
Figure 7-1 illustrate,s a BASIC

cfd.

""II"""""""""'1""T
Irnrnrnrnrnrnrnillillillrnillrnrnrnrnrnrnrnrnrnrnillrnrnrnrnrnrnillillmill~

Irnrnrnrnrnillrnillrnrnillrnrnrnrnrnmrnrnrnillrnillillrnillrnrnrnillillillill~

~~~D~D~"-'~
... h'~~~~~ffiffi~ffiffiffiffi~ffiffiffiffiffi~ffi~ffiffi~ffiffi~~~ffiffiffiffi~
fiJ [iJ [i] "J ~ 'I ~ (j] ~m. IJ leu
oo..fiiJ 91ft;] m[ilJ [ij] (j] ~ [1] ill [1] ~ ~
:lJ Wru 'J ·f,.'1 ['fj [jJ l] , ilbD:lllj I)] I
to OJ tdlUlJ ~l Ell L'l [] [jJ Ell OJ ~l ~ ~
I] m 3 ..., ,f· llj ~ rll ~ ~ ~ [j] ~J ~ 00 Ell ~J [1J ~ Ell t~ ~ rn ~ !1l E!l 00 E!l ~ ru crJ ~ [ij] [ij] Ell EiJ [!!J t!l f1] 8
. 00 ")"',,,f, 'n EiJ BJ I1l EiJ Im~~ fl]
E!J tlj ffi ~ EiJ EiJ EiJ EiJ EiJ t:!] Ell ~
ill@] @J "" F 'IJ f1] f1J Ell ~ I!lftifiJtn1I~ ~l
MOftU ffi Ell ~ [t l'lJ ~ Ell Ell Ell ~ ~ 8

ernrnu
ern

B.oltn

~OOOO- ~~ffi~BJBJBJmm~ffi~~ffi~~BJEiJBJ~~~~~~~ffi~BJ~~~~~~~
7 r~~1~~E!lE!l~mmE!lm[ij]OOrnE!lffirn(j][ij][ij]rllE!l~ffirnffi~~[ij][ij](j]~E!lE!l[ij]S

l!lOO 8 "'''.&, ffi~~~[;Jffiffi~OO~~~~~~ffi~~~l1]fj]l1]~~OO~~~~l1]~~~ ~
@]~

9 .' .......

I 2 3 4

'ffi~~~ffiffi~]ffiOO~~[;][;]OO~~OO~~[j]ffi~[;j~OO[;J~~ffi~~~~

• 1 IU II II 12 1l!J4!J5IJIII1!J1I 1m! 211221231241251211211211211301311321331341 351311311311311

Figure 7-1.

EduSystem 30 BASIC Card

Program statements are written onto e BASIC cards by marking these boxes with ordinary lead penc . Each box is marked with
a single heavy line, drawn either verti ally or diagonally. It is not
necessary to fill in the entire box. Av, id making any stray marks,
7-18

as the- computer reads all marks on the card, whether or not they
occur inside a box. Any stray marks cause the computer to misread
the card. A program to be submitted to EduSystem 30 is marked
on a series of these cards; each program statement is placed on a
separate card.
LINE NUMBERS
The first item of each program statement to be marked on the
card is the line number. All program statements must have line
. numbers from 1 to 999. The line number is marked in the leftmost
three columns of the card. In each of these columns are 10 boxes
containing the digits 0 through 9. (Above these numbered boxes
are six other bo:xes which are never marked as part of a program
statement. They are used as control cards and are explained later.) The user marks an appropriate digit in each of three columns.
If the line number is only one or two digits, it can be marked in
any of the three columns. Blank line number columns are ignored.
Figure 7-2 shows a card marked with the line number 120~

Figure 7-2.

Line Number Example

Line numbers should be marked on cards in "the order in which
program statements are to be executed: the lowest line number on
the first cay;d, the highest line number (the END statement) on the
last card. If the cards are not physically qrdered by line number
within the card deck, EduSystem 30 still executes the program in
line-number order. The only time when- the order of the cards is
important is when two cards have the same line number. In that
7-19

case, only the last card in the deck which has that line number is
used in the program.
BASIC STATEMENTS
BASIC statement types are marked after the line number, in
column 4 or 5, within the outliI1ed area. Each box in this area
represents a single BASIC statement; thus, one mark in the appropriate box indicates the corresponding statement type. It is not necessary to spell out the statement. Since each statement is marked
on a separate card, each program card should have only one mark
in column 4 or 5. In Figure 7-3, the LET box has been marked.
Line 120 is, therefore, a LET statement. (The implied LET cannot be used with card programs.)

Figure 7-3.

Statement Example

STATEMENT OPERAND
The line number and statement type are marked in specific sections of the card. The remaindec of a statement, the statement
operand, is marked in a different manner in columns 6 through 39.
The first step in this process is to write the remaining characters of
the line in the boxes across the top of the card, one character to a
box, starting in column 6. The boxes below each of these cqaracters
are then marked with the aid of the BASIC template, a~ shown in
Figure 7-4.
7-20

+ -

$&OEFIA()<>
o?

! G H 110 B - I t ; 0

: J K L

1J H F
paR 1 M K I [
STU 1 P N L $
V w· x 1 s a o 7
y z
1v T R :
. 1Y W U
It ."
1. z X
; , \ I .

M N 0

2
3
4
5

E C'II

Il -

(

7 ...

)

8 I <
9 t

2
3

& 5

! 6

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8
9

EDUSYSTEM-30
BASIC TEMPLATE

momODma

Maynard, Massachusetts

Figure 7-4.

EduSystem 30 BASIC Template

The template has a column of holes down the center with the
characters used in writing an operand printed on either side. All
characters are printed twice on the template, once on the left and
once on the right. The top hole in the template corresponds to the
blank boxes at the top edge of the card where the characters of the
operand were written. The bottom pair of holes correspond to
the row of heavy black marks along the lower edge of each card.
The twelve holes in between correspond to the twelve boxes in
eachcard column.
The following procedure is used to mark the statement operand
characters:
11, Place the template on the card so that the character to
be marked appears in the top box of the template and the
two black marks appear in the bottom pair of holes.
2 .. If the character is a digit (0 to 9), find that digit on
either side of the template and mark the one box which
is beside that digit.

7-21

3. If the character is not a digit, find the two occurrences
of that character on the template, one on the left and one
on the right. Mark the two boxes which are beside these
characters.
4. If the character is a space, make no marks.

An example of the marking procedure is shown in Figure 7-5.

EDUSYSTEM-30
BASIC TEMPLATE

(

mamDDma

Maynard. Massachusetts

Figure 7-5.

Marking the Statement Operand

,I'

SUMMARY OF CARD MARKING PROCEDURE
A completed card is :tnarked in three places:

1. Columns 1 through 3 to mark the lin.e number.
2. Column 4 or 5 to indicate the BASIC statement type.
3. Columns 6 through 39 to indicate the statement operand,
as w!itten across the top of the card.
Figure 7-6 shows two examples of completed cards.
7-22

Figure 7-6.

Completed BASIC Cards

Submitting a Program to be Run

When all statements of a program have been marked on cards,
the cards are collected into a single deck for submission to the
computer. However, in addition to the deck of program cards,
the computer must be given the program name and explicitly instructed to execute the program. Special cards, called control
~ards, are added to program deck for this purpose. Control cards
are not part of the actual program. They do not have line numbers
and are placed ~t the beginning and end of the program deck.
7-23

THE NEW CARD
The first card of any deck submitted to the computer must be a
NEW card or an OLD card 4 (see Using a Stored Program), which
contains the name of the program. Any cards in a deck which
come before a NEW, or OLD, card are ignored. If no NEW, or
OLD, card is included in the deck, the entire program is ignored.
A NEW card has a single mark in the NEW box in the upper
left-hand corner of the card. It has no other marks in columns 1
through 5. The name of the program, which can be 1 to 6 characters long, is marked using the template and starting in column 6.
The remaining columns of the NEW card, starting in column 12,
should be used to mark identifying information such as the name
of the programmer.
THE LIST CARD
When the computer reads a program, it reads the marks in the
columns rather than the characters printed across the top of the
card. If the columns below each character are accurately marked,
the computer reads the card as intended. Erroneous marks, however, cause, the computer to read the statements incorrectly. It is
useful to obtain a printed listing of the program exactly as it
was read by the computer. The LIST command instructs the computer to print such a listing. A LIST card contains a single mark in
the LIST box, the topmost box in column 3. The LIST card
should be placed after the program deck,· immediately before the
RUN card.
THE RUN CARD
Each program deck submitted to the computer must have a
RUN card following the last program card. A RUN card has a
single mark in the RUN box, the topmost box in column 2. The
RUN card is the signal for the computer to execute the program.
If a program deck has no RUN card, the program is loaded into
the computer but never executed. The RUN card is normally the
last card in the deck.
Since the NEW (or OLD) card is the first card in the deck, it is often
marked on a colored card to make it easy to spot the beginning of separate programs in a stack of many programs. Control cards can be easily
identified if the system manager runs a felt-tip marker over the tops of a
box of cards and makes these cards available to students for use as control cards.
4

7-24

SUMMARY
A complete program deck, ready to be run by the computer,
consists of the complete set of program cards preceded by a NEW·
card and followed by a LIST and/or a RUN card. If other control cards are being used, they may be iriserted as necessary. Control cards should be placed before or after the program deck,
not inserted within it. This complete deck is then submitted to the
computer operator to be run. (If there is no system operator, each
student must run his own program through the computer as
described under Executing Card Programs.) Figure 7-7 shows a
.
BASIC program deck.
~

'"2
UJ

III

:::>

.,:

'"0

.,:

'"0
U

,..:

11.

'"<-'

u,
,..:
11.

'"<-'

!::

£!
Q

Figure 7-7.

BASIC Program Deck

Getting the Results of a Computer Run
Whenever EduSystem 30 processes a card program, it prints
the results of that run on the Teletype. The ,format of this output
is as follows:
\

1. Beginning of Output-A row of dashes (- - - -'- -)
is printed to indicate the beginning of program output
and thus separate each program from the output of the
previous program.
2. Identification Line-The information on the NEW card
is printed at the top of the first page of output. This information usually includes the name of the program and
the name of the programmer.
7-25

3. Program Listing-If a LIST card is included directly
after the program deck, a listing of all statements in the
program is printed. It is preceded by a header line which
includes the name of the program and a short message
selected by the system operator.
4. Program Output-If a RUN card is included at the end
of the deck, the program is executed. The results of all
PRINT statements are printed as program output. The
printed program output is preceded by the same header
as the program listing.

Using a Stored Program
In all previous examples the program to be executed is submitted on a card deck. The NEW card at the front of the deck
indicates that the program to be run is a new one (i.e., a program the computer does not already have stored away) and that
it is contained in the cards which follow the NEW card. The
computer is also capable of storing programs for future use.
Stored programs are considered -to be old programs. They do not
have to be submitted on cards each time they are run.
An OLD card is used to call a program which has been stored
in the system previously. The OLD card has a single mark in the
OLD box in column 1 of the card. All programs stored within
the system have names. The name of the old program to be used
must be marked starting in column 6. The user must be certain
to use exactly the same program name as he used when he first
identified the program. For example, blanks which preceded the
program name or appear in the name itself must be included. The
OLD card is used instead of a NEW card; it is, therefore, the first
card in the deck. Like the NEW card, it should have identifying
information coded in the columns after the program name. (Like
the NEW card, OLD is often marked on a colored card.)
Since the program is already stored in the system, the OLD
card need not be followed by a program deck. The next card
can be the RUN card. Two cards, an OLD card followed by a
RUN card, are all that is needed to run a stored program. If the
user wishes to supply some of his own input data to an OLD
program, this data is marked as regular DATA statement cards.
These DATA cards are placed between the OLD card and the
7-26

RuN card. They 'are merged into the stored program before it is
executed. 5

Interacting With the Operator
If card programs are being run under the supervision of a system operator, he may be requested to perform certain functions,
such as entering data or making minor modifications to the
program.
An OPR card is used to communicate with the operator. An
OPR card has a single mark in the OPR box in column 4 of the
card. Any message can be marked in columns 6 through 39. When
an OPR card is encountered in a program deck, the· message in
columns 6 through 39 is printed and a bell rings to alert the
operator.
Normally, the OPR card is used to request the operator to perform some function which a card user cannot perform directly.
Operations such as saving programs in the system storage area
can only be done by typing commands at the Teletype.
A KEY card is used to have the computer pause so that the
operator can type one or more commands. The KEY card contains a 'single mark in the KEY box in column 2 of the card; it
should be the last card in the deck. KEY should, of course, be
preceded by one or more OPR cards, telling the operator what
to do when the computer pauses. For example, BASIC programs
can request data from the operator. An INPUT statement is used
to request data from the Teletype, such as the current date.
Editing and Rerunning a Program
After a program has been executed by means of a RUN card,
it is still available in core memory and may be modified and/or
run a second time. New lines, or new data, may be added to the
program, or, may replace existing program statements. Any program lines to be added should follow the first RUN card. After
these new cards, a second RUN card should be included. The
The DATA statements submitted on cards must have line numbers which
differ from the line numbers of the stored program. Otherwise, these
DATA statements will replace program statements. Also a stored program which is to be used with card data should have no DATA statements of its own.
5

7-27

number of RUN cards allowed per deck
operator and is normally two.

set by the system

Inserting Messages in the Program Printout

One line messages can be inserted into program output by
using an MSG card. An MSG card has a single mark in the MSG.
box in column 3 of the card. Columns 6 through 39 can contain
any message. This message is printed as part of the program output.
Sample Program

The following sample program demonstrates the use of EduSystem 30 as a computational tool by students who have no knowledge of computer programming. The program is already stored in
the computer.
PROBLEM
Students in a physics class are performing a lab experiment
whose results require very lengthy data reduction. Rather than
have each student perform these· calculations manually, the instructor wrote a program to do it and stored the program under
the name LAB3 7. This program has no line numbers between
900 and 950. Each student is to prepare a deck containing his
data, in some predefined order with line numbers between 900
and 950, and submit it to the computer.
PROCEDURES
Each student prepares a deck containing his data and submits
it to the computer. The decks are prepared in the following manner:

1. Each student writes his lab data values across the top
of one or more cards, starting in column 6. Values on any
one card are separated by a comma.
2. When all data values have been obtained, the student
completes the marking of the data cards. The DATA
box in column 5 of each card is marked. The first card
is marked with line number 900 in columns 1 to 3. Succeeding cards are given line numbers 901, 902, etc.
Finally, using a template, the student fills in the boxes in
columns 6 through 39.
3. An OLD card is marked with a single mark in the OLD
box, the program name LAB37 in col.umns 6-10, and the
student's name after column 11. The OLD card is placed
7-28

before the data deck. Next a RUN card, with a single
mark in RUN box is placed behind the deck. These cards
are then submitted to the computer.
PRINTED RESULTS
The following is a sample printout of the results of one student's
input to the LAB37 _program:
OLD LAB37

A. EINSTEIN

PHYSICS

RUN
LAB37

EDUBASIC

DATA SET

SAMPLE SIZE
12
SUM = 444
MEAN
37
STD. DEVIATION = 7.51665

DATA SET

~~,~
,
"if -_/I

SAt1PLE SIZE = 8
SUM = 32.7
MEAN = 4.0875
STD. DEVIATION

EXECUT
-.-.'
- Once" EduSystem 3 as een oaded"and started, it is available
for processing program decks (if the batch capability was retained
at system load time). It is not necessary to reload or restart the
system each time it is used.
-~--,.,.

"'>

-- \
~--------

Perform the following operations to process batch (multiple'
programs) of marked cards. Collect all programs to be run into a i
single deck. Any number of programs may be included so long as I
the deck fits into the card reader (maximum of 400 cards).
,i
i

1. Arrange all cards so that they face in the same direction. f
2. Place the deck in the reader, face down with the row of !
black marks on the bottom of each card placed inward ,r
toward the back of the reader.
7-29

3. Ensure that the reader power switch is ON, then press
the START button. At this time, all red lights on the
card reader conttol panel should be off; the single green
light should be on.
4. Type BATCH. The BATCH command is used to commence processing of the entire batch of programs loaded
into the reader.
Once a batch run is initiated, it continues until all cards have been
processed. EduSystem 30 then asks:
MORE CARDS?

5. Type N if no more programs are to be executed during
this run. EduSystem 30 concludes the batch run by typing
READY. If more programs are to be executed, continue at steR 6.
6. Place the. additional program cards in the reader, then
press S!ART. Respond to the MORE CARDS? question
by typing Y. The batch operation restarts.
All output from a batch is printed at the Teletype (or possibly
on a line printer, see Using Optional Hardware). The output of
individual programs is separated by rows of dashes (- - - - - - ) ..
Executing Card Programs Individually

EduSystem 30. may be used as a system in which each user
loads and executes his own card program. The system is started
exactly as it is for a batch run; the BATCH command is typed,
even though no cards are in the reader. The system, finding no
cards, asks:
MORE CARDS?

At this time the system is ready to accommodate a single user
with a card deck. The single user can proceed with the op-erating
procedures· described under Normal Batch Operation. When all "
cards have been processed, the system again asks:
MORE CARDS?

7-30

The user may then tear off his program output and leave the system ready for the next user.
Controlling a Batch Run

A batch operator may control the execution of card programs.
CTRL/C may be typed at any time to terminate a program run
and automatically continue with the next program. CTRL/C does
not interrupt the loading of a program, only its execution or listing. When CTRL/C is used to terminate program execution, the
message STOPPED BY OPERATOR is printed.
The ALT MODE key (labeled ESC on some terminals) may
be used to interrupt the system while it is reading cards (i.e., halt
the batch operation) and allow the operator to type commands
at the Teletype. The operator can then type BATCH to begin
processing of the next program in the deck.
Several optional commands (BATCH, MAX, 'HEADER,
ST ACK, and LOG) are available to modify and control a batch
run. All of these commands are privileged commands (see Privileged Control Commands). They can be used only if privileged
command capability was retained at system load time and if the
user knows the correct password.
BATCH COMMAND
In the privileged mode, the BATCH command may be followed
by a single space and an integer which is less than 4000. For
example:
BATCH 20

This number is the maximum number of RUN commands which
may be executed by any single program deck. If privileged commands are not enabled or if no number is specified, the BATCH
command is executed and 2 is the number of RUN commands
( cards) allowed per program.
\, MAX COMMAND
Occasionally, a program is submitted which does not terminate.
It will run indefinitely (in a loop) and delay the execution. of
other programs until the operator stops it The MAX command
can be used to automatically terminate programs which run too
long. MAX defines the maximum number of BASIC program
•
7-31

statements which may be executed in a program. The system
counts instructions in units of 200. Thus, the limit set by the
MAX command is the number of 200 instruction units which are
allowed per program. If very small programs are being run, a
MAX of 10, allowing execution of 2000 statements, is reasonable.
This command is typed as follows:
MAX 10

More complex programs need to execute more than 2000 statements. In this case, a correspondingly higher limit should be set.
If no MAX is set, or if the operand of MAX is 0, programs may
be run indefinitely. A MAX limit is only in effect for the succeeding batch run. If the program being run executes a CHAIN
instruction, the instruction count is restarted.
HEADER COMMAND
Before running or listing a program, the system prints a header
line consisting of the name of the program followed by the message
EDU BASIC. The HEADER command may be used to change
this message to any new header composed of 1 to 12 characters.
The new header is then used for all programs in the next batch
run. Thus, this command can be used to identify the programs in
that batch. For example, if a batch consists of all the programs
\ from a given class, the name of the class or of the instructor might
be used for the header. To use the HEADER command, type
HEADER and press RETURN; then type the new header message
and press RETURN again. For example:
HEADER
PHYSICS 101

STACK COMMAND
The KEY command and the INPUT statement may be used by
a card program to interact with the operator, as described previously. When a batch is being processed unattended, these commands stop program execution. Therefore, the STACK command
is available to start up an unattended batch run. The STACK
command makes all INPUT and KEY instructions illegal and
causes processing of card programs to begin. Like the BATCH
command in privileged mode, the STACK command may be followed by a space and an integer which specifies the number of

•

7-32

RUN commands allowed per program. For example, if the STACK
command is typed as:
..
STACK 4

it allows any program to be executed four times. This number is
2 by default if not explicitly specified or if the system is not in
privileged mode. Execution of BATCH, STACK, NEW, or OLD
commancis automatically locks out the privileged instructions. Subsequent privileged instructions must be preceded by a successful
PRIVILEGE command.
LOG COMMAND
As programs are run, a system log is created which contains
a record of all the programs which have been run. More specifically, the log retains all information included on the NEW or OLD
card which precedes each program deck. NEVv' or OLD cards
generally contain such information as the name and cl.ass of the
student who submitted the program. The privileged command LOG
may be used to obtain a printed listing of this log.
If a very large number of programs are run before the log is
printed, or if the amount of space reserved for the log when the 1\
system was loaded is small, the log may become full; if this hap- (\) i
pens, the log is automatically printed at that time without a LOG:\
command being given.
.._, _. __ .. __~..
(. \\

--'---.',-----..',. '

·'-~---l'··~

Hands-On Interaction Versus Batch
If the user wishes to get maximum throughput of student programs, he should use the ST ACK command. However, if the
user wishes' to allow hands-on student int(~raction with a hign
throughput, he uses the BATCH command and implements the
plan outlined below.
Most student interaction in programming occurs during debugging. The EduSystem 30 BATCH command allows the user to
mix hand-on use with high throughput. Typing BATCH with no
following number allows each program to be run a maximum of
two' tiines. A programming class use of EduSystem 30 is optimized by ,entering cards in the following order:

NEW program name
caId deck

student, class
7-33

I
f

I
I

LIST card
RUN card
KEY card
EduSystem 30 reads 'the deck, lists the program, and attempts
execution. The student's error messages print at this time, if errors
occur, and the KEY card allows the student to sit down at the
terminal and correct the errors on-line. When errors have been
corrected, the student types his second RUN,. getting his second
attempt at execution. Upon completion of the second RUN, EduSystem 30 automatically reads the next student's cards.
This use of BATCH with the KEY cards allows each student
two successive attempts at a successful RUN and brings much
of the excitement of interaction into the EduSystem 30 batch
operation.
ERROR MESSAGES

Some programs execute' correctly the first time they are tried.
Most others, especially if they are at all complex, have errors in
them. EduSystem 30 checks all statements and commands when
they are entered (on cards or from the interactive terminal) and
before executing them. If it cannot execute a statement or command, the system informs the user by printing one of the following
types of messages.
.
Batch Mode Program Loading Errors

The following messages are printed if errors occur while BASIC
is loading a card program.
Message

.Explanation

BAD CHARACTER

One or more characters on a card were· not
understood. The character % replaces any
unreadable character. The information on the
card is processed if possible. This error does
not cause any subsequent RUN commands
to be ignored.
BAD CHARACTER- Same as BAD CHARACTER message except
LINE NOT USED
that the information on the card is ignored.
This error does cause subsequent RUN commands to be ignored.
.
WHAT?
Line does not make sense to the system. It
does not begin with a line number and is not
a valid system command or statement;
I

7-34

Message
NO ROOM

FILE NOT SAVED
FILE TOO BIG
FOR BATCH MODE

Explanation
The program is too large to be loaded, i.e.,
it is greater than 5000 characters. Larger programs should be run in interactive mode or
CHAINed.
The progra~ named on an OLD control card
is not available in the system storage area.
The program named on an OLD card is too
large to be run in batch mode. It mus(be run
interactively.

Interactive Mode Program Loading ErrorsH

As each line is typed, EduSystem 30 checks it for program loading errors. If it finds an eqor, it prints one of the following error
messages immediately after the erroneous line.
Explanation

Message
WHAT?
LINE NO. TOO BIG
LINE TOO LONG
NO ROOM
FILE NOT SAVED
NO SPACE
Bell
I/O ERROR

INVALID
PASSWORD

Line does not make sense' to the system. It
does not begin with a line number and is not
a valid system command.
The line number of a line or the' argument of
a system command is greater than 4095.
Line just entered is longer than 80 characters.
There is no room to store the line just entered.
The program named as the operand of an
OLD command was not previously saved on
the system device.
There is not enough space on the DECtape
to SAVE the current program.
If an invalid character is entered, the Teletype bell rings and the character is ignored.
An input or output error occurred on the
DECtape unit. Be sure that the unit is on-line,
write-enabled, and the unit number is set correctly. Retry whatever was interrupted by the
error. If the problem persists, there is a hardware problem. Contact the system administrator or DEC field service.
The password typed after a PRIVILEGE
command is not the system password. Privileged mode is not entered.

To correct program loading and coding errors indicated by these messages,
the appropriate line in the program must be corrected in the manner described in the Program Editing section, Procedure 2.
6

7-35

Coding Errors

After the RUN (or RUNNH) command is entered, EduSystem
30 checks each statement before executing it for mistakes in the
BASIC program coding. If the system cannot execute a statement,
it informs the user by printing one of the following messages and
the line number in which the error was found.
Message

Explanation

CH
'EN

There is an illegal character in the line.
Program does not have an END statement as the last line
in the program.
Not enough NEXT statements in the program. There must
be a NEXT statement for each FOR statemellt in the program.
FOR and NEXT statements do not match. There is a
NEXT statement: in the program whose variable is not the
same as the variable in the corresponding FOR statement.
Line contains an improperly written decimal number or
constant.. It may, for example, have two decimal points or
have an alphabetic character in it.
The program as a whole is too big to be run by the sys- .
tern. Making the program smaller, reducing the size of .
subscripted variables, or using the NOLINE command
may help.
Program has too many (more than 8) FOR-NEXT loops
one within another.
Line contains an improperly used parenthesis. Generally,
the problem is an expression which does not have an equal
number of left and right parentheses.
Statement contains an invalid relational operator _«, =,
>, <=, >=). Relational operators may only be used in IF
statements.
Statement as a whole is not properly written and, as a result, does not conform to proper BASIC syntax. For example, a semicolon is aHowed in a PRINT statement but
not in a READ or INPUT statement.
Statement word is not one of' the legal BASIC statement
types.
The program is too big to be run. Cause is usually an extremely large number of PRINT statements.

Fa
LI
M1
M2

NE
PC
RO

S1
S2
ST
TB

7 To correct the program loading and coding errors indicated by the
messages, the appropriate' line in the program must be corrected in the
manner described in the Program Editing section, Procedure 2.

7-36

Message

Explanation

Program :is either too large or too complex to be run. The
total number of variables, constants, functions, and line
numbers should be reduced, if possible.
A GOSUB, GOTO, or IF statement contains a line number
which does not exist.
A quotation mark indicating the beginning of a 'String of
text does not have a corresponding quotation mark at the
end of the text string.

Program Logic Errors 8

Some errors do not show up until the program is actually executed. An example of this type of error is an expression which uses
a square root of a variable. If, when this square root is actually
calculated, the variable has a negative value, a program logic error
has occurred. EduSystem 30 prints the following messages if program logic errors occur.
Message

Explanation

A CHAIN statement tried to chain to a program which
was not available in the DECtape storage area.
Program ran too long and was automatically stopped by
the system.
The program ran out of data. It attempted to do a READ
after all data had been read.
The program attempted to divide by zero. Instead of dividing by zero, BASIC divides by the smallest possible number, giving a result of about 10 500 • This error does not
cause the program to stop.
An expression coptains a function which was not defined
in a DEF statement.
The program is too complex to be executed. The problem
is generally that too many subroutines have themselves
executed GOSUB instructions.
Program attempted to take the logarithm of a negative
number or zero.
A RETURN statement was used outside of ;a subroutine
or a subroutine was entered by a GOTO instead of a
GOSUB.
See GS.

CO
DA
DO

FN
GS
LG
RE
SP

8 Some program logic errors may be corrected by the method described
in the Program Editing section, Procedure 2. Most, however, necessitate
the rewriting of the program.

7-37

Message

Explanation

Program attempted to take the square root of a negative
number. BASIC automatically takes the square root of the
absolute value of the number instead. This error does not
cause the program to stop.
Program used a sUbscript which was too big for the variable. The maximum size of a subscript is specified in a
DIM'statement.
There is no r,oom to write data. The program attempted to
do a WRITE statement when the data list was full. (Note
that if this error occurs, the program text will no longer
be intact. A NEW, OLD, or SCRATCH command must
be used to clear the program area.)

SS
WR

OPERATING INSTRUCTIONS
Loading EduSystem 30'
The EduSystem 30 software is supplied on a paper tape. This
tape must be loaded into computer memory when the system is first
installed. Once loaded, the software need not be reloaded. Perform
the following procedures to load the EduSystem 30 software.

INITIALIZE THE DECDISK
If the system device is DECdisk, perform the following steps to
prepare the disk for software loading:
1. Ensure that the disk unit is on (red light illuminated inside the back of the computer cabinet) .
2. Ensure that all disk protect switches (located inside the
front of the computer cabinet) are III the off (down)
position.
INITIALIZE THE DECTAPE UNIT
If the system device is a DECtape unit, perform the following
steps to prepare the unit for software loading.
1. Set the REMOTE/OFF/LOCAL switch to OFF.
2. Place a DECtape on the left spindle with the DECtape
label out.
3. Wind four turns of tape onto the empty reel on the right
spindle.
4. Set the REMOTE/OFF/LOCAL switch to LOCAL.
S. Wind a few turns of tape onto the right spindle reel with
the ~ switch to ensure that the tape is properly mounted.
7-38

6. Dial 0 on the unit selector dial.
7. Set the REMOTE/OFF/LOCAL switch to REMOTE.
8. Set the WRITE ENABLE/WRITE LOCK switch to
WRITE ENABLE.
INITIALIZE COl\1PUTER MEMORY
The EduSystem 30 software tape may be loaded into memory in
one of two ways: with an automatic loader (hardware bootstraps)
or with the Read-In Mode (RIM) loader program. The following
loading instructions are for an EduSystem 30 that includes a hardware bootstrap. If the EduSystem does not have a hardware bootstrap, see Appendix A for instructions on using the RIM loader.
1. Turn the key lock on the computer console to POWER.
2. Turn the Teletype to LINE.
3. Place the EduSystem 30 tape in the appropriate reader
(high-speed or Teletype) with the leader code (ASCII
. 200) over the read head.
4. Set the SWITCH REGISTER (SR) to 5356 (octal).9
5. Press and raise the HALT switch.
6. Turn on the appropriate paper tape reader.
7. Press and raise the SW switch.
The tape should begin to move. If it does not, ensure that the
correct tape is being used and that tape is positioned. over the read
head. Repeat the above procedures.
System Building Dialog
When a portion of the EDUSYSTEM-30 paper tape has been
read, BASIC prints a series of questions (see Figure 7-8) concerning the system configuration. The user responds by typing Y
for yes and N for no, followed by the RETURN key. The first
question is:
STANDARD SYSTEM?

EduSystem 30 has several optional operating modes and may be
used with a variety of hardware components. A response of Y to
the above question causes EduSystem 30 to build a system as it
An explanation of the octal. or base 8, number system is included in
Introduction to Programming 1972.

7-39

would if the following answers were given to the other system
building questions:
IS SYSTEM DEVICE A DF32 IHSK?Y
HOW MANY DISKS?1
DO YOU WANT BATCH CAPABILITIES?Y
HOW MANY BLOCKS FOR LOG?6
BATCH INPUT ON PUNCHED CARDS?N
DO YOU WANT PRIVILEGED COMMAND CAPA8ILITY?Y
TYPE INITIAL PASSWORD
(EDU-BASIC)
DO THE FOLLOWING EXIST:
HIGH-SPEED PUNCH?N
LP08 PRINTER?N

Basic then asks:
PROGRAM LIBRARY INITIALLY EMPTY?

The user respondsY if there are no programs to be saved on the
system device. If programs are to be saved, the response must be
N and the questions in boxes 1 through 8 of Figure 7-8 must be
answered in the same way as \Yhen the system was built.
If the user types N in response to the question STANDARD
SYSTEM?, EduSystem 30 recognizes that a nonstandard system is
being loaded and asks the following questions:
IS SYSTEM DEVICE A DF32. DISK?
f TC01
DECTAPE?
RF(ilJ8 DISK?
LINCTAPE?
TO BE DECTAPE?

This series of questions is asked only until a response of Y is
typed. If the device being described is not the one being used in
the system, the user responds ,by typing N. If the system device is
a disk, either DF32 or RF08, the system asks:
HOW MANY DISKS?

The user responds by typing the number of disk surfaces available
in the system (1, 2, 3, or 4) and then typing the RETURN key.
If the system device is TD8E DECtape, the system asks:
7-40

DO YOU HAVE A TDBE ROM?

Respond Y if the system has a TD8E Read-Only Memory. If the
response is N, the system asks:
8K OF CORE?

If the system device is DECtape, the system must include either
a TD8E ROM (TD8E DECtape only) or 8K of core memory. If
the response to the previous question was Y, this question is not
asked.
EduSystem 30 then asks:
DO YOU WANT BATCH CAPABILITIES?

If. the system is to process card programs, respond Y. If it is only
to be used as an interactive system, respond N. If batch capability
is selected, the system then asks:
HOW MANY BLOCKS FOR LOG?

The log is a stored record of system usage which records the
name of all programs submitted for execution. The larger it is:. the
more program runs may be recorded before the log becomes full
and must be printed. The log may be from 0 (no log at all) to 22
blocks of disk storage. Each block will hold the record of approximately 10 to 20 programs. Respond by typing the number of blocks
to be reserved for the batch log, then typing the RETURN key. The
system then asks:
BATCH INPUT ON PUNCHED CARDS?

Respond N if the batch input is to be coded with the EduSystem
30 template on the standard 39-column EduSystem 30 mark-sense
cards. Respond Y if input will be on cards punche4 using a keypunch.
The system then asks:
MAXIMUM DATA COLUMNS PER CARD?

7-41

The maximum allowable response to this question depends upon
the type of reader used: the punched-card reader has a maximum
of 80 columns per card; the mark-sense reader maximum is 40
columns per card. See Using Optional Hardware for more information on preparing cards using a keypunch.
Next, the system asks:
DO YOU WANT PRIVILEGED COMMAND CAPABILITY?

The privileged command capability prevents unauthorized users
from executing certain critical system commands. To establish this
protection, type Y.
The system then prints:
. TYPE INITIAL PASSWORD

The password is a special code which must be known in order to
use privileged commands. It is up to six characters long. Respond
by typing the desired system password. If it is less than six characters, type the RETURN key after the last letter of the password.
To protect their secrecy, the characters typed are not printed. If
no privileged capability is desired, the response to the original
question is N. (A standard sys~em keeps the privileged capability
and sets the initial password to BASIC.)
Finally, the system asks if a high-speed paper tape punch and/or
line printer are part of the system by printing:
DO THE FOLLOWING EXIST:
HIGH-SPEED PUNCH?
LPc;,8 PRINTER?

The response to each question must be Y if the device exists, N
if it does not. A standard system assumes that neither device exists.
(See Using Optional Hardware for a discussion of how these devices are used.)
When all questions have been answered, the system asks:
IS THE ABOVE CORRECT?

If all questions were answered properly, type Y. The system then
loads the rest of the EduSystem 30 papet tape. If any of the re-

7-42

sponses were incorrect, type N; the complete set of questions is
repeated.
When the entire tape has been read, EduSystem 30 gives the
user a chance to load additional DEC-supplied system update tapes
by asking:
MORE INPUT?

If no DEC-supplied ,update tapes exist, respond Nand EduSystem
30 is completely loaded. If update tapes do exist, load the first

one into the tape reader and type Y to obtain loading.
Finally, when all input has been read, EduSystem 30 indicates
that it is ready to process BASIC programs by printing:
READY

At this time, turn the key lock to PANEL LOCK and remove the
key to prevent the system from being accidentally disturbed.
DIAGNOSTIC MESSAGES DURING SYSTEM BUILD
The following error messages are printed when errors are detected during the building of EduSystem 30.
TAPE READY?

This message is printed whenever the system is waiting for the
paper tape reader to be loaded. It may appear by itself, usually
due to a tape tear or reader jam, or it may appear as. the last line
of another diagnostic message.
ACTION:
1. The portion of the paper tape which is read after the
system building dialog has distinct blocks of information
about two and one-half tape fanfolds long. The start of
such a block is indicated by nine blank tape frames followed by a frame with all positions punched.
Back up the tape several fanfolds to the beginning of a
previously read block. Position the tape such that the
blanks at the beginning of the block are over the read .
station.
2. Type Y on the interactive terminal.
7-43

1-4

Figure 7-8.

System Building Dialog

7-44

l-------'

Figure 7-8 (Cont.).

System Building Dialog

7-45

BEGINS READING
TAPE AND
BUILDS SYSTEM

YES

READS IN
·ADDITIONAL
INPUT

WHEN TAPE
IS READ,
u
TYPES " READY

Figure 7-8 (Cont.).

System Building Dialog

7-46

BAD PLACE TO START TAPE
TAPE READY?

This message means that after a previous message the user did
not correctly position the tape to the beginning of a data block.
(See discussion under TAPE READY? message.)
ACTION:
1. Correctly position the tape.
2. Type Y on the interactive terminal.
CHECKSUM ERROR
TAPE READY?

A checksum error occurred while the most recent data block
was being used.
ACTION:
1. Back up the tape to the beginning of the block.
2. Type Y to reread the data.
SYSTEM DEVICE liD ERROR

If this message occurs before the dialog has been completed, the
dialog automatically restarts.
If an I/O error occurs after the dialog is completed,. the TAPE
READY message is printed.

ACTION:
1. Make sure that the system device is on-line and writt!enabled and that the unit number is set correctly.
2. Respond appropriately to the question which follows the
message.
Turning Off the System
If power failure detection is available on the EduSystem 30,

simply turn the console key lock to OFF. Otherwise, to shut the
system down, overnight or for any reason, ensure that the system
is inactive by:
7-47

1. Typing CTRL/C to stop any program that is running.
2. Turning the key lock to POWER, and pressing and raising
the HALT switch.
3. Turning the key lock to OFF.
NOTE
Turning off the computer does not turn off
the disk unit. Disk power should never be
turned off.
Turning On the System
If power failure detection is available on the EduSystem 30,
simply turn the key lock to PANEL LOCK. Otherwise, perform
the following procedures.
1.
2.
3.
4.
5.
6.

Ensure~

that the hardware is properly initialized as explained previously.
Turn the key lock to POWER.
Set the.5R to 0000 and press EXTD ADDR LOAD.
Set the SR to 7600 and press ADDR LOAD.
Turn the Teletype to LINE.
Turn the key lock to PANEL LOCK.

EduSystem 30 is now ready to process BASIC programs.
Restarting EduSystem 30
If EduSystem 30 has been loaded onto the system device but the
computer memory has been used to run other programs (which do
not write on the system device), then the following device-dependent programs may be used to start up the system. Instructions
for these programs are given in octal numbers. If unfamiliar with
the octal, or base 8, number system, refer to Introduction to Programming 1972.
DF32 OR RF08 DISK
With hardware bootstrap:
1. Press and raise the HALT switch.
2. Set the SR to 5350.
3. Press and raise the SW switch.
Without hardware bootstrap:
1. Press and raise the HALT switch.
7-48

2.
3.
4.
5.
6.
7.
8.
9.

Set the SR to 7750 and press ADDR LOAD.
Set the SR to 7600 and lift DEP.
Set the SR to 6603 and lift DEP.
Set the SR to 6622 and lift DEP.
Set the SR to 5352 and lift DEP.
Set the SR to 5752 and lift DEP.
Set the SR to 7750 and press ADDR LOAD.
Press the CLEAR switch, then the CONT switch.

TCOIDECTAPE
With hardware bootstrap:
1. Press and raise the HALT switch.
2. Set the SR to 0600.
3. Press and raise the SW switch.
Without hardware bootstrap:
1.
2.
3.
4.

5.
6.
7.
8.
9.
10.
11.
12.
13.
14.

Press and raise the HALT switch.
Set the SR to 7742 and press ADDR LOAD.
Set the SR to 1353 and lift DEP.
Set the SR to 6766 and lift DEP.
Set the SR to 6771 and lift DEP.
Set the SR to 5344 and lift DEP.
Set the SR to 1352 and lift DEP.
Set the SR to 5343 and lift DEP.
Set the SR to 7752 and press ADDR LOAD.
Set the SR to 0220 and lift DEP.
Set the SR to 0600 and lift DEP.
Set the SR to 7577 and lift DEP, then lift DEP again.
Set the SR to 7742 and press ADDR LOAD.:
Press the CLEAR switch, then the CaNT switch.
L

TD8E DECTAPE
With TD8E ROM:
1. Press and raise the HALT switch.
2. Set the SR to 7470.
3. Press, in order, the ADDR LOAD, EXTD ADDR LOAD,
CLEAR, and CONT switches.
Without TD8E ROM:
1. Press and raise the HALT switch.
7-49

2.
3.
4.
S.

Set the SR to 0011.
Press the EXTD ADDR LOAD switch.
Set the SR to 7470 and press ADDR LOAD.
Press the CLEAR switch, then the CONT switch.

Using Optional Hardware

LP08 LINE PRINTER
If the EduSystem 30 includes an LP08 line printer, perform the
following procedures to produce output on the -line printer rather
than at the Teletype.
1. Turn the LP08 power switch to ON.
2. Turn the ON-LINE/OFF-LINE switch to ON-LINE.
3 .. Type LPT and press RETURN.
4. When printing is complete, type TTY and press RETURN.
5. Turn the LP08 power switch to OFF.
An LPT command causes all subsequent output associated with
LIST, LOG, RUN, CATALOG, BATCH, or STACK commands
to be printed on the LP08 printer. A TTY command returns control to the Teletype from the line printer. The user may temporarily interrupt printing by turning the ON-LINE/OFF-LINE
switch to OFF-LINE; he may continue printing by turning it to
ON-LINE. When batch processing terminates, the output device
is automatically reset back to the Teletype.
HIGH-SPEED PAPER TAPE READER/PUNCH
If a high-speed punch is available, the PUNCH command may
be used to punch the current program on paper tape .. PUNCH
may be used with or without an argument. It is similar to LIST in
that the entire program is punched if no argument is used and, if
an argument is used, only those lines numbered greater than or
equal to that argument are punched. Perform the following procedures to use the high-speed punch:
1.
2.
3.
4.
5.

Turn the TTY control knob to LINE.
Turn the high-speed punch ON.
Press FEED to produce some leader tape.
Type PUNCH and press RETURN.
When punching is complete, press FEED to produce some
trailer tape.
6. Turn the high-speed punch OFF.
7-50

Punching tp.ay be stopped at any time by typing CTRL/C.
If a high-speed reader is available, the TAPE command may be
used to load BASIC programs previously punched on tape. Perform
the following procedures to use the high-speed reader:
1.
2.
3.
4.
5.

Turn the high-speed reader ON.
Turn the TTY control knob to LINE.
Insert tape in the reader.
Type TAPE and press RETURN.
When the tape has read in, turn the high-speed reader
OFF.
6. Type KEY; press RETURN.

A KEY command returns control to the Teletype.
PUNCHED CARD INPUT
Programs loaded and run via the card reader may be prepared
using a standard DEC 029 keypunch or be marked with a lead
pencil arid the EduSystem 30 template. If punched cards are used,
the system building dialog questions must be answered appropriately.
Punch program statements on cards just as if they were being
typed at the interactive terminal. The seven control commands
(NEW, RUN, LIST, OLD, KEY, MSG, and aPR)· available in
batch mode are used by punching the command name starting in
column 1. Information normally marked starting in column 6 must
begin in column 5.
The number of data columns on each card which
is read by
,
EduSystem 30 is specified in the system building dialog. Thus the
system can be made to ignore the latter portion of a batch input
card. These ignored columns then may be used to hold sequence
numbers or other information which will not be processed by
EduSystem 30.
Programs .punched with a keypunch may be read by either the
regular DEC punched card reader (CR8 series) or the DEC
mark-sense reader (CM8 series). With the punched card reader,
standard 80-column cards may contain up to 80 columns of data.
Cards to be read by the mark-sense reader must be· punched on
cards which have the special marks along the bottom edge of the
card and which conform to other rigid specifications.
The mark-sense cards may be made to contain up to forty
.

7-51

columns of data per card. The simplest, and recommended, method
for using 'punched mark-sense cards involves using the standard
EduSystem 30, cards. Ignore the information printed on the card.
Prepare a keypunch' drum card· which will cause the punches to
occur only in keypunch columns 1, 3, 7, 11, 13, ... , that is in
all the odd numbered columns except column 9. All other columns
should be automatically skipped. The user may now punch EduSystem 30 cards as if they were normal cards. The drum card will
correctly position the punches. Note that the BASlC commands
must be punched in their entirety.
CALCULATING AVAILABLE STORAGE
The number of storage blocks initially available on the syst€m
device is calculated according to the following rules:

Availabie Blocks

1. System' Device
DF32 Disk
DECtape
RF08 Disk
LINCtape

131
1348
1922
1348

2. If batch capabilities are included in the system, subtract 10
blocks from the basic number of blocks. If the number of
blocks specified for use by the batch log is greater than one,
subtract one less than that number from the current total.
3. If the system device is a disk and the hardware configuration
includes more than a single disk surface, add the appropriate
number of blocks for each additional disk surface.
System Device

Available Blocks

DS32,
RS08

255
2046

7-52

8
edusysten.... 40
INTRODUCTION
EduSystem 40 offers a combination of the language capabilities
of EduSystem 20 and EduSystem 30 by allowing the user to nm
either system, but not both simultaneously. The purchaser of an
EduSystem 40 is obtaining an extremely versatile system-one
which can accommodate not only a large and varied number of
users, but a tremendous number of program runs per day. Working with EduSystem 20, the beginning student, who is unfamiliar
with a computer system and who may be learning a computer language for the first time, can develop his skills while as many as
seven other students may also be using the system at equal or
more advanced levels of learning. If the problem is complex or the
student desires the use of commands not present in EduSystem 20,
then EduSystem 30 is available as a stand-alone system. In addition, using the batch capabilities of EduSystem 30 permits extremely large numbers of user programs on cards to be executed
every day.
With the varied services provided by EduSystem 30 and, alter,..
nately, the time-sharing capabilities of EduSystem 20, the user
obtains a complete system which can be put to use continuously
for maximum produetivity.
System Components
EduSystem 40 is composed of a PDP-8/E computer with 8192
words of core memory (12,288 words of core memory are recommended if the syste:m includes 5 or more terminals); automatic
loader (MI8-EF or MI8-EO hardware bootstrap, MI8-EC for
TD8-E DECtape with ROM'; 32,768 word DECdisk (DF32
or RF08) or DECtape; optical mark sense card reader; and as
many as eight Teletype termipals with low-speed paper tape reader
and punch units. Each EduSystem 40 contains two BASIC Language processors (EduSystem 40-20 and EduSystem 40-30) and
a library of "sample programs, textbooks and curriculum guides.
8-1

Optional components include a high-speed line printer, high-speed
paper tape reader and punch, and additional core memory to increase program SIZe.

System Expansion
By adding 4096 words of core memory; a high-speed paper
tape reader; 262,000 word DECdisk and control; additional computer terminals and their associated interfacing; and an EduSystem
50 software set, EduSystem 40 may be expanded to EduSystem 50.
(Chapter 9 provides information concerning the EduSystem 50
TSS-8 time-sharing system.)
If the system includes DECtape, the PDP-8 Operating System
(OS/8) m!ly be run. This system contains a keyboard monitor,
machine language. assemblers, debugging tools, and FORTRAN,
and is described in Chapter 9 of Introduction To Programming
1972.
.
BASIC LANGUAGE CAPABILITIES
Advantages and Applications
EduSystem 40 provides the user with two BASIC systemsEduSystem 40-20 and EduSystem 40-30. Both systems are fairly
compatible in language capabilities-they share a large number of
common statements and commands. However, there are certain
features peculiar to each EduSystem which may make it advantageous for the user to choose one over the other. A short summary' of these features is included here. (The user is directed to
Chapters 5 and 7 for complete details concerning the use of the
language capabilities of EduSystems 20 and 30).
EDUSYSTEM 20
EduSystem 20 provides an immediate mode for fast and accurate calculations of expressions and equations. Statements used in
this mode are not stored in memory.
There are certain commands available in EduSystem 20 which
are either not pres~nt in EduSystem 30 or are used in a different
way. The more important of these are EDIT, INPUT. DIM.
IF THEN, ON GOTO, and ON GOSUB.
, The EDIT command speeds the editing procedure by eliminating the need to retype complete lines. The user simply searches
for the character(s) he wishes to change and, using the options
available, makes the necessary corrections.

8-2

The INPUT statement allows a number or numbers to be entered from the Teletype as values for variables. Using EduSystem
20, the user response may be a value, or a mathematical expression which may contain arithmetic operations and a ~ASIC function (see Tables 8-4 and 8-5).
The DIM statement is not necessary in EduSystem 20 as the
system sets limits on subscript size (single subscript: 0-2047; double subscript: 0-63 for each subscript), and defines all variables
as they occur.
.
The IF THEN statement, in addition to conditionally altering
the order of execution by effecting transfer of control, may include another BASIC statement, thus causing an operation to be
performed without changing the order of execution.
The ON GOTO and ON GOSUB statements allow conditional
transfer to another statement or subroutine depending upon the
integer value of the formula following ON. After execution of a
subroutine, control returns to the statement following the ON
GOSUB statement.
It has already been mentioned that EduSystem 20 is a multiuser BASIC, and as far as the school system is concerned, this is
probably its greatest asset. As many as eight users may be working simultaneously on one computer. Terminals may be situated
in different rooms, even different buildings, to serve a greater
number of users and applications.
EDUSYSTEM 30
EduSystem 30 is a true batch system allowing either interactive
or "hands-off" batch operation. Specially formatted mark cards
provide a means by which students can easBy code programs and
submit a deck for later execution. An operator can gather all individual program decks into one large deck, to be run consecutively and automatically by the system. Commands are available
which allow operator intervention during runs.
EduSystem 30 makes available to the user a single mass storage
device-DECdisk (or DECtape). The user can store data files or
sections of very long programs which will later be chained together. He can also save programs which may be used later or
which may be called more than once. Several special commands
called Privilege Control Commands are associated with the mass
storage device. Among them are commands which will save and
8-3

delete programs, determine the amount of available core, list programs in storage, arid list the number of blocks in use.
EduSystem 30 includes a CHAIN command which makes progr~m chaining possible and allows th~ running of' programs of any
length. Each section of the entire program must be 6000 characters or less and is stored on the mass storage device. Data files
may be used in a similiar manner by allowing temporary storage
of data on the mass· storage device. Using WRITE statements,
data may be written onto files; data stored in these files is called
into a program via READ statements.
EduSystem 30 includes a character-handling feature which allows words or characters to be entered into a BASIC program in
response to questions. The special .characters # and $ are used to
facilitate this procedure. Characters are stored as their respective
numeric codes and. therefore may be used and manipulated with
standard BASIC commands. The ASCII codes for these characters
may be found in Appendix B.
For detailed· information concerning the features mentioned in
this section, and all other available language capabilities, the user
should refer to Chapter 5 when using EduSystem 20 and Chapter
7 when using EduSystem 30.
Language Summaries and Error Message Summaries follow.
LANGUAGE SUMMARIES
BASIC Statements and Commands
Table 8-1 lists the statements available in EduSystems 20 and
30; Table 8-2 summarizes the editing and control commands. These
tables are abbreviated forms of those contained in Chapters 5
and 7.

Table 8·1.

Statement

Statements

Description

& Format

EduSystem
20 30

Input! Output
DATA n1' n:! •.. nn

Nllmbers n1 through nn equal
variables in a READ
Get VI through Vn input from

TrY
8-4

Table 8·1. (Cont.)
Statement
& Format

RESTORE
WRITE n 1 , n2' .. nn

Statements

Description
Print values of specified text,
variables or expressions; also
used for format-control
Read variables VI through Vn
from DATA list
Reset DATA pointer to beginning value
Record DATA nl through nn
on mass storage file

EduSyste:m
20 30

x x
x x
x

x
x

Transfer of Control
GOTOn

Transfer control to line
number n
If relatio'nship r between el and
e2 is true, transfer control to
line number n
Same as IF GO TO; under
EduSystem 20 n may be a
statement
Conditionally change order of
program execution according
to evaluation of formula el
(if integer of el =1 transfer
control to nl; if integer of
e 1 =2, transfer to n:h etc.)
Conditionally change order of
program execution according
to evaluation of formula el
(if integer of el = 1 transfer
control t6 subroutine n t ; if
integer of el =2 transfer to
subroutine n:!; if integer of el =3
transfer to subroutine n;)

DIM v(nl), v(n2' n;:)

Define subscripted variables

x x

FOR v=el TO e;!
STEP e:\

Set up program loop; define v
values beginning at e 1 to e2
incremented by ea
Termipate program loop; incre. ment valu~ of v until v>e;!
(in FOR statement)

IF el r e;! GO TO n
~f

el r e;! THEN n

ON el GO TO n 1 ,

ON el GOSUB n 1 ,
n;!. n:\

x
x

x x

Loops and Subscripts

NEXT v

8-5

Table 8.1 (Cont.)
Statement
& Format

EduSystem
20 30

Subroutines
GOSUB n
RETURN
STOP
Others
CHAIN on' $
DEF FNA (x) =f(x)
DEF FNA (x, y)=
f(x, y)
END
LETv=f
-RANDOMIZE
REM text
NOLINE

CAT

CTRL/C
DELn
n
DELn,m
EDln c
KEY

Description

Enter subroutine at line .
number n
Returnfrom subroutine to statement following GOSUB
Transfer control to END
statement

x x

Link to next section of a
program which is stored'
within the system as file n
Define a function

x
x x

End of a program
Assign value of formula f to v
Randomizes random number
routine
Insert a remark or comment
Suppress printing of line numbers
in which program logic errors
are found

Table 8-2.
Command
& Format

Statements

x x
x x
x x
x

Edit and Control Commands
Description

List names of programs in storage.
area
Stop program execution: return to
edit phase
Delete line n
Delete line n
Delete lines n through m inclusive
Search line n for character c typed
following carriage return
Return to keyboard mode after
TAPE (EduSystem 30-HSR only)

8-6

EduSystem
20 30
x

x
x

Table 8-2. (Cont.)

Command

Edit and Control Commands

Description

& Format

LIST
LISTn
LISTn
LISTn,m
LISTNH
LISTNH n
NEW
OLD
RUN
RUNNH
SCR
BYE
TAPE

BATCH
"'BATCHn
ECHO
LPT
LENGTH
NAME
PUNCH
PUNCHn
PTP
PTR
RESEQUENCE
TTY

EduSystem
20 30

List entire program in core (If lowspeed punch is on, EduSystem 20
will cause a tape to be punched)
List program starting at line n
List line n only
List lines n through m inclusive
List program; no header (If lowspeed punch is on, program will
be punched on paper tape)
List program beginning at line n;
no header
Clear core; request program name
Clear core; bring program to core
from storage area
Compile and run program in core
Same as RUN; no header
Erase current program from core
Same as SCR
Read paper tape from low-speed
reader; suppress printing on TTY
(also used with high-speed reader
under EduSystem 30)
Commence batch processing
Same as BATCH; limits runs to n
per program
Switch from typeout to non-typeout
mode or vice versa when using
low-speed reader
Print output on lineprinter, if
available
Request number of blocks to store
current program
Same as NEW but does not delete
existing program
Punch entire program on paper tape
Punch program starting at line n
Punch a program out on the high-speed
paper tape punch.
Read program from high-speed reader
Renumber program lines
Print output on TTY

8-7

x
x

x
x
x

x x
x

x
x
x
x
x
x
x
x
x

x
x
x
x

Table 8-2. (Cont.)

Edit and Control Commands
Description

Command
& Format

PRIVILEGE
(password)
*HEADER
(header)
*LOG
*MAXn

* PASSWORD
(new· password)
*SAVE
*STACK
*STACK n
*UNSAVE
>I<

Enable use of privileged commands
Insert password, no echo
Change header; type new header
(max. 12 characters) for next
batch run
Print system10g
Set instruction limit n times 200 per
program for next batch run
Change password
Type new password, no echo
Save program in storage area
. Start unattended batch operation
Same as STACK; limit runs per
program
Delete program from storage area

EduSystem
20 30

x
x

Privileged Mode Command

Batch Control Cards
The control cards in Table 8-3 are used when running an Edu. System 30 batch card deck. The user must mark the appropriate
box in the upper left hand corner of the EduSystem 30 mark card.
Each control card is explained in detail in Chapter 7.
Table 8-3.
Control
Card

Batch Control Cards.

Description

NEW

Indicates a new program; contains the new program name;
must be first card in the deck-any cards appearing before·
this card are ignored.

OLD

Indicates an old program; contains the name of the program to be caned; must be first card in the deck-any cards
appearing before this card are ignored.

MSG

Columns 6-39 contain a message which is printed as part
of program output.

OPR

Message marked in columns 6-39; when encountered in
program execution rings bell to alert operator and prints
message on TTY.
~-8

Table 8··3. (Cont.)
Control
Card

Batch Control Cards
Description

KEY

Temporarily halts the batch operation and turns control
over to the console terminal.

LIST

Instructs computer to print a listing of the program on the
TTY. Should be placed at the end of the card deck before
the RUN card.

RUN

Normally the last card in the deck; instructs the computer
to begin execution.

BASIC Functions and Arithmetic Operations
Table 8-4 lists the functions available in EduSystem 20 and 30.
Table 8-5 is true for all EduSystems.

Table 8-4.

Functions

Function

Description

SQR(x)
SIN(x)
COS(x)
TAN(x)
ATN(x)

Square root of x (Yx)
Sine of x (x in radians)
Cosine of x (x in radians)
Tangent of x (x in radians)
Arctangent of x
(x in radians)
(result in radians)
eX (e=2.712818)
Natural log of x (logex)
Absolute value of x (Ixl)
Greatest integer of x
Sign of x ( + 1 if positive, -1 if negative,
o if zero)
Random number between 0 and 1
Truncates decimal portion of x
Controls printing head position on TTY.
Converts character code to character.
Used only with PRINT command.

EXP(x)
LOG(x)
ABS(x)
INT(x)
SGN(x)
RND(x)
FIX(x)
TAB(x)
CHR$(x)

EduSystem
20 30
x
x
x
x

x
x
x
x

x
x

x
x
x
x

x
x
x

x
I

8-9

Table8~5.

Arithmetic Operations

Symbols

Meaning

exponentiation
multiplication
division
addition
subtraction

'"
+
/

1.
2.
3.
4.

Order of Execution
parenthetical expressions
exponentiation
multiplicatio~ and division
addition and subtraction

ERROR MESSAGE SUMMARIES
EduSystem 20
EduSystem 20 checks all commands be(ore execution. If an error
is found, it prints one of the error messages in Table 8-6 and the
number of the line in which the error occurred.

Table 8·6.

EduSystem 20 Error Messages

Message

Explanation

WHAT?
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR

2
3
4

5
6
7

ERROR
ERROR

8
9

ERROR
ERROR
ERROR
ERROR
ERROR

10
11
12
13
14

Command not understood. It does not begin with a
line number and is not a valid system command.
Log of negative or zero number was requested.
Square root of negative number was requested.
Division by zero was requested.
Overflow--exponent greater than approximately +38.
Underflow---exponent less than approximately -38.
Line too long or program too big.
Characters are being typed too fast; use TAPE command for reading paper tapes.
System overload caused character to be lost.
Program too complex or too many variables. (GOSUB,
FOR, or user-defined function calls are too deeply
nested.)
.
Missing or illegal operand or double operators.
Missing operator before a left parenthesis.
Missing or illegal number.
Too many digits in number.
No DEF for function call.

8-10

Table 8.6. (Cont.)

EduSystem 20 Error Messages

Message

Explanation

ERROR 15.

Missing or mismatched parentheses or illegal dummy
variable in DEF.
Wrong number of arguments in DEF call.
Illegal character in DEF expression.
Missing or illegal variable.
Single and double subscripted variables with the same:
name.
Subscript out. of range.
No left parenthesis in function.
Illegal user-defined function-not FN followed by a
letter and a left parenthesis.
Mismatched parentheses or missing operator after
right parenthesis.
Syntax error in GOTO.
Syntax error in RESTORE.
Syntax error in GOSUB.
Syntax error in ON.
Index out of range in ON.
Syntax error in RETURN.
RETURN without GOSUB.
Missing left parenthesis in TAB function.
Syntax error in PRINT.
An unavailable device was requested by the user-the device is either not present in the system, or in
use.
Missing or illegal line number.
Attempt to GOTO or GOSUB to a nonexistent line.
Missing or illegal relation in IF.
Syntax error in IF.
Missing equal sign or' improper variable left of the
equal sign in LET or FOR.
Subscripted index in FOR.
Syntax error in FOR.
FOR without NEXT.
Syntax error in LET.
Syntax error in NEXT.
NEXT without FOR.
Too much data typed or illegal character in DATA
or the data typed in.
Illegal character or function in INPUT or READ.
Out of data.
Unrecognized command during execution.

ERROR
ERROR
ERROR
ERROR

16
17
18
19

ERROR 20
ERROR 21
ERROR 22
ERROR 23
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR

24
25
26
27
28
29
30
31
32
33

ERROR
ERROR
ERROR
ERROR
ERROR

34
35
36
37
38

ERROR
ERROR
ERROR
ERROR
ERROR
ERROR
ERROR

39
40
41
42
43
44
45

ERROR 46
ERROR 47
ERROR 48

8-11

If
. f
s the
1U orm

·
0
ERRORS
.
EduSystem 3 DE PROGRAM LOADING d b fore execution.

BATCH MO
h cks all cornman s e·
EduSystem 30 also c e
d 'EduSystem 30
cute a cornman,
7
it is unable to exe
es in Table 8- .
user by printing one of the error messag

TableS-'.

Batch Mode Program Loading Errors

Message

Explanation

BAD CHARACTER

One or more characters on a card could not
be understood. The character % replaces
any unreadable character. The information
on the card is processed if possible. This
error does not cause any subsequent RUN
commands to be ignored.

BAD CHARACTERLINE NOT USED

Same as BAD CHARACTER message except that the information on the card is
ignored. This error does cause any subsequent RUN commands to be ignored.

WHAT?

Line does not make sense to the system. It
does not begin with a line number and is not
a valid system command.

NO ROOM

The program is too big to be loaded, i.e. it
is greater than 5000 characters. Larger programs should be run in interactive mode.

FILE NOT SAVED

The program named on an OLD control
card is not available in the system storage
area.

FILE TOO BIG FOR
BATCH MODE

The program named on an OLD card is too
big· to be run in batch mode. It must be run
interactively.

INTERACTIVE MODE PROGRAM LOADING ERRORS
As each line is typed, a check is made for program loading errors. If an error is found, one of the messages in Table 8-8 is
printed immediately after the line containing the error.

8-12

Table ,8-8.

Interactive Mode Program Loading Errors

Message

Explanation

WHAT?

Line does not make sense to the system.
It does not begin with a line number and
is not a valid system command.

LINE NO. TOO BIG

The line number of a line or the argumem
of a system command is greater than 4095 .

LINE TOO LONG

. Line just entered is longer than 80 char··
acters.

NO ROOM

There is no room to store the line just
entered.

FILE NOT SAVED

The program named as the operand of an
OLD command was not previously saved
on the system device.

NO SPACE

There is not enough space to SAVE the
current program (DECtape Systems).

Bell

If an invalid character is entered, the Tele..

type bell rings and the character is ignored.
II 0 ERROR

An input or output error occurred on the
DECtape unit. Be sure that the unit is on·
line, write-enabled, and the unit number is
set correctly. Retry whatever was interrupted by the error. If the problem persists,
there is a hardware problem (DECtape
Systems).

INVALID PASSWORD

The password typed after a PRIVILEGE
command is not the system password. Priv··
ileged mode is not entered.

CODING ERRORS
After the RUN or RUNNH command, but before execution,
EduSystem 30 checks for mistakes in the BASIC program coding.
,If an error is found, one of the following messages and the appropriate line number is printed.
8-13

Table '8-9. ,Coding Errors

Message

Explanation

There is an illegal character in the line.

Program does not have an END statement as the last line
in the program.

- Not enough NEXT statements in the program. There
must be a NEXT statement for each FOR statement in
the program.

FOR and NEXT statements do not match. There is a
NEXT statement in the program whose variable is not
the same as the variable in the corresponding FOR
statement.

LI ,

Line contains an improperly written decimal number or
constant. It may, for example, have two decimal points
or have an alphabetic character in it.

M1
M2

The program as a whole is too big to be run by the systern. Making the program smaller, reducing the size of
subscripted variables, or using the, NOLINE command
may help.

Program has too many (more than 8) nested FOR-NEXT
loops.
'

Line contains an improperly used parenthesis. Generally,
the problem is an expression which does riot have an
equal number of left and right parentheses.

Statement contains an invalid relational operator
=,
>, <=, >=). Relational operators may only be used in
IF statements.

SI
S2

Statement as a whole is not, properly written and, as a
result, does not conform to proper BASIC syntax. For
example, a semicolon is allowed in a PRINT statement
but not in a READ or INPUT statement.

Statement cbmmand word is not one of the BASIC statement types.

The program is too big to be run. Cause is usually an
extremely large number of PRINT statements.

Program is either too big or too complex to be run. The
total number of variables, constants, functions, and line
numbers should be reduced, if possible.

«,

8-14

Table 8-9. (Cont.)

Coding Errors

Message

Explanation

A GOSUB, GOTO, or IF statement contains a line number which does not exist.

A quotation mark indicating the beginning of a string of
text does not have a corresponding quotation mark at the:
end of the text string.

PROGRAM LOGIC ERRORS
If a program logic error occurs, EduSystem 20 prints one of the:
messages in Table 8-10 after execution.
Table 8·10.

Program Logic Errors

Message

Explanation

A CHAIN statement tried to chain to a program which
was not available in the DECtape storage area.

Program ran too long and was automatically stopped by
the system.

The program ran out of data. It attempted to do a READ
after all data had been read.

The program attempted to divide by zero. Instead of
dividing by zero, BASIC divides by the smallest possible
number, giving a result of about 10 500 • This error does
not cause the-program to stop.

An expression contains a function which was not defined
in aDEF statement.

The program is too complex to be executed. The problem
is generally that too many subroutines have themselves
executed GOSUB instructions.

Program attempted to take the logarithm of a negative;:
number or zero.

A RETURN statement was used outside a subroutim~
or a subroutine was entered by a GOTO instead of a
GOSUB.

Same as OS.

Program attempted to take the square root of a negative
number. BASIC automatically takes the square root of
the absolute value of the number instead. This error does
not cause the program to stop.

8-15

Table 8-10. (Cont.)

Program Logic Errors

Message

Explanation

Program used a sUbscript which was too big for the variable. The maximum size of a subscript is specified in a
DIM statement.

There is no more room to write data. The program attempted to execute a WRITE statement when the data list
was full. (Note that if this error occurs, the program text
will no longer be intact. 'A NEW, OLD, or SCRATCH
command must be used to clear the program area.)

LOADING AND OPERATING INSTRUCTIONS
The software for EduSystem 40 is distributed on five paper tapes
-.EduSystem 40-20 and EduSystem 40-30 for Disk Systems, and
individual EduSystem 20 and EduSystem 30 tapes for DECtape
Systems. The us'er with a DECtape System should refer to Chapters
5 and 7 for loading and oper'lting instructions as the following instructions refer only to the standard Disk System. The EduSystem
40-20 and 40-30 tapes are used to build the EduSystem 40 system
on DECdisk (either DF32 or RF08) when the system is installed.
The building procedure is outlined below.
Initializing the DECdisk
Initialize the DECdisk by ensuring thai the disk unit is turned on
~nd that all disk protect switches are in the off position.
Building EduSystem 40 on Disk
The system tapes may be loaded into memory by use of either
the RIM Loader (refer to Appendix A) or with the automatic
loader (hardware bootstrap MI8-EF or MI8-EG).
1. Turn the key Jock on the computer console to POWER.
2. Turn the Teletype to LINE.
3. Place the EduSystem 40-20 tape in the appropriate reader
(high or low-speed) with the leader code (ASCII 200)
over the read head.
4. If the system contains a hardware bootstrap, set the
SR == 5356; press and raise the HALT switch; press and
raise the SW switch.
8-16

5. If using the RIM loader, set the SR = 7756: press and
raise ADDR LOAD, CLEAR and CONT.
6. Turn the reader on.
The tape should begin to move (if it does not, be sure the correct
tape is being used and repeat the above procedure). When the tape
has been read completely, the system prints the following message
on the Teletype:
IS SYSTEM DEVICE A DF32 DISK?

The user should respond Y or N. If the response is N, the system
asks:
IS SYSTEM DEVICE AN RF08 DISK?

The answer here should be Y; otherwise the system will repeat both
questions until the answer to one of them is Y. When the correct
system device has been specified, the system prints:
EDUSYSTEM 20

BASIC

NUMBER OF USERSCl TO 8)?

At this point halt the computer by pressing and raising the HALT
switch. (If the above messages are not printed, the above procedure
should be repeated before continuing the building process.)
7. Place the EduSystem 40-30 tape in the appropriate reader.
8. If the system contains a hardware bootstrap, set the
SR = 5356; press and raise the SW switch.
0000; press EXTD ADDR
9. Otherwise, set the SR
LOAD; then set the SR
7756; press ADDR LOAD,
CLEAR and CONT.

=
=

Approximately one-third of the tape should be read before the
standard EduSystem 30 dialogue begins. The system will print:
STANDARD SYSTEM?

Build EduSystem 30 as detailed in Chapter 7 and summarized below. The user is at point A on. the flowchart in Figure 8-1 and
should continue with the dialogue presented in the flowchart. (If Y
is typed as a response to this question, the system assumes the
responses contained in brackets on the flowchart.)

8-17

HOW MANY DISKS

(USER RESPONDS
FROM 1-4)

[1]

HOW MANY BLOCKS
FOR LOG ?
(USER RESPONDS

FRO~~-22)

[N]

MAXIMUM DATA
COLUMNS PER CARD

(USER RESPONDS
FROM 0-80)

Figure 8-1.

Building EduSystem 40

8-18

TYPE INITIAL
PASSWORD (USER
TYPES A WORD
OF 6 OR LESS
CHARACTERS) (BASIC)

TAPE READS

Figure 8-1. (Cont.)

Building EduSystem 40

8-19

When EduSystcm 40 prints READY on the Teletype, the disk
is completely built and ready to bc used, with EduSystem 30
runmng.
Starting EduSystem 40

Once EduSystem 40 has been bullt on the disk, it can be stopped
and restarted by performing the following operations.
1. Press and raise the HALT switch.
2. A. If the system does not have a hardware bootstrap, the
following instructions must be manually loaded:
~

Set SR=7750 and press ADDR LOAD.
Set SR=7600 and lift DEP.
Set SR=6603 and lift DEP.
Set SR=6622 and lift DEP.
SetSR=5352 and lift DEP.
Set SR=5752 and lift DEP.
Set SR=7750 and press ADDR LOAD, CLEAR and
CONT.
B. If the system contains a hardware bootstrap set the SR=
5350 and press and raise the SW switch.
The system should respond by printing:

EDUSYSTEM 40-SELECT (1=20,2=30):

If thc system does not respond in this manner, repeat the starting'

instructions; if the system does respond as it should, the user is at
point A on the flowchart in Figure 8-2 and should continue with
the dialogue in that flowchart. ,

8-20

s)
EDUSYSTEM 40
SELECT{1-20,2-3O)'
?
NU~ER Of
USERS (1-8)
USER RESPONDS

RO~~

----]

TELIiTYPE
< 17>
<"17>
< 1 7>
<12>

1•

BLOCKS

1 • BLOCKS

1 • BLOCKS
1 • BLOCKS
·2. BLOCKS

.BIN
.TMP
.TMP
.BAS
.FCL

< 17>
< 17>
<17>
<17>
<12>

1•
1•
1•
1•
2.

BLOCKS
BLOCKS
BLOCKS
BLOCKS
BLOCKS

:S
DELETED
DELETED
S

JOB
I. USER (3,13) LOGGED OFF K00 AT 10:46:07 ON
DELETED
3 FILES (
3. DISK BLOCKS>
SAVED 2 FILES (
3. DISK BLOCKS)
RUNTIME 00:00:25 ( 2. CPU UNITS)
ELAPSED TIME 00:06:12

9 JUN 70

In the previous example, the user typed a question mark to
check the LOGOUT options. When LOGOUT completed the
printed explanation, it printed CONFIRM: and waited for a user
reply. In this case, the user requested a listing of his files. LOGOUT followed this listing with a second CONFIRM: to which the
user replied I. When using the 1 option, the user is advised not to
type his reply to individual entries until printing stops. DELETED
is printed automatically by the system to show that the temporary
files are deleted without user intervention. The user saved binary
file FIE and the FOCAL file PROG. The BASIC file INTER
was deleted by typing the RETURN key.
9-9

Table 9-1. ,LOGOUT Options

Option
:S

Function
Save all nontemporary files. A temporary file is one of the
following:
BASOnn
BASlnn
TEMPnn
where nn is the console number at which the user is logged
into the system. A temporary file is created by a System
Library Program and listed in CATALOG listings. A temporary file is also considered to be any file with a .TMP
extension. If no option is specified in the LOGOUT command, :S is the default.

Delete all unprotected files from disk.

List the user's file dire~tory. After listing the files, the system prints CONFIRM: and the user replies with one of
the options.

Allow the user to individually decide which files to save
or delete. Temporary files are deleted automatically.

Print a listing of the available options and their functions.

An optional method of logging out of the system is to type K
in response to the Monitor dot or K followed by a colon and an
option designation. For example:
.K
JOB 01 1 USER (1234,ABCD) LOGGED OFF K13 AT 14:28:02 ON 02-28-73
SAVED 3 FILES ( .4. DISK BLOCKS)
RUNTIME 00:00:07 (
1. CPU UNITS)
ELAPSED TIME 00:13:57

System Library Program Control
Once logged into the system, the user can call any EduSystem
50 System Library Program.' To call a library program, the user
9-10

types the command R (meaning run) followed by one or more
spaces and the program name. For example:
.R BASIC
NEW OR OLD--

The Monitor fetches the BASIC language processor from the
System Library and starts it. BASIC begins its dialog by asking
if the user wishes to work on a new program or retrieve an old
one from disk storage. Notice that once BASIC begins, the console is no longer in ~.1onitor mode. Dots are no longer printed at
the margin. An input is now processed by the BASIC language
processor.
If the user types a program name which cannot be found in the
System Li,Qrary, the Monitor responds with an error message and
returns the console to the Monitor mode, as follows:
.R BASICK
FILE NOT FOUND?

•

The exact contents ofa System Library may vary from installation to installation. The System Manager may choose to make any
number of programs available to a11 users.
Communication with Other Users
Although EduSystem 50 gives each system user the impression
that she is the only user of the system, it is actually supporting many
users ata time. Often it is useful to communicate with another
user or with the system operator; this is done with the TALK command. The TALK command requests the Monitor to print a message on another system terminal. For example, a user at terminal
7 can ask the system operator to turn on the high-speed punch by
typing the following command (the initial dot is printed by the
Monitor) :
.TALK

e PLEASE TURN ON THE HIGH-SPEED PUNCH.

The above command causes the following to be printed at console O.
. **Ke7** PLEASE TUI=iN ON THE HIGH-SPEED PUNCH.

9-11

**K07** indicates that terminal 7 sent the message. Any terminal can initiate a message to any other terminal. However, if the
destination terminal is printing at that time, the message will not
be sent. The initiating terminal would, in this case, receive the message BUSY as a response.
System Status Reports
The command SYSTAT initiates a printout of the full status of
EduSystem 50, how many users are on-line, what they are doing,
etc. The command SYSTAT is equivalent to typing R SYSTAT.
The format of the status report is described in the section on
Utility Programs.
The user can obtain information on the amount of computer
time used by him, the amount used by another user, or obtain
the time of day with the TIME command. The TIME command
can be issued in one of the following three forms:
TIME

. TIME 0
TIMEn

Returns the elapsed processor time of the
user issuing the TIME command since he
logged into the system.
Returns the time of day .
Returns the amount of processor time used
by job n since logging into the system.

For example:
.TIME
00100100

.TIME 0
17121106

.TIME UJ
00100134

Resource Sharing
All system users, when logged into the system, have access to
the System Library, disk storage, a virtual 4K PDP-8, and the
EduSystem 50 Monitor. The Monitor handles disk resource requests automatically. The Monitor also maintains a pool of available devices which are assigned to users upon request on a
first-come, first-served basis. Devices such as the high-speed paper9-12

tape reader cannot, by their very nature, be assigned to severa:l
programs simultaneously. Therefore, the Monitor grants individuall
users exclusive access to these devices when needed. Deviees such
as the system disk, and sometimes DECtapes, are not assigned
since they can be used by more than one user simultaneously.
All systems include a high-speed paper-tape reader in the pool
of available devices. Many systems also include a high-speed paper··
tape punch, high-speed line printer, and one or more DECtapes"
These assignable devices are normally used with the System Library
Programs PIP and COpy to store programs or data on paper tape
or as DECtape flies.
When a device is assignable (present on the system) and avail··
able (not being used), the ASSIGN command may be used to
reserve the desired unit or units for exclusive use by the console
issuing the command. The valid ASSIGN commands are for··
matted as shown below:
ASSIGN R
ASSIGN P
ASSIGN 0
ASSIGN L

Assign the high-speed paper-tape reader.
Assign the high-speed paper-tape punch
and line printer.
Assign a DECtape unit.
Assign the line printer and high-speed
punch.

If other devices are assignable, the System Manager will inform
the user of the appropriate device designator. The following is an
example of using an invalid device designator:
.ASS I GN X
ILLEGAL REQUEST

The Monitor ignores the request, responds with the appropriate
message, and prints another dot. When a valid ASSIGN command
is issued, the Monitor checks the availability of the device and re·sponds accordingly. For example:
.A.SSIGN R
R ASS I GNED
.A.SSIGN P
JOB 02 HAS P

9-13

When the system contains multiple units of a device, the user
simply specifies the device; the Monitor assigns an available unit
and responds with the unit number. For example:
.ASSIGN D
D 0 ASSIGNED

If all DECtape units are busy, the Monitor prints the message
shown below:
.ASSIGN D
DEVICE NOT AVAILABLE

A specific unit can be requested by leaving a space between the
device designator and the device number. For example:
.ASSIGN D "

D " ASSIGNED

NOTE
If the user assigns a device with a nonexis-

tent device number, that device will not be
assigned; an error message does not result
because that device is not busy. An error
message only results when the device is already assigned.
The ASSIGN command assigns only one device at a time. Therefore, when multiple devices are to be assigned, each must be assigned separately. The following will not accomplish the desired
assignments, either with or without the illegal commas .
• ASSIGN R, D 2, 'D
R ASSIGNED

The Monitor accepted the first device designator and ignored the
rest of the command. If device R is unavailable, the Monitor prints

9-14

the appropriate message. The following commands complete the
desired assignments (assuming available devices) :

.ASSIGN D 2
D 2 ASSIGNED
.ASSIGN D 1
D 1 ASSI GNED

•

When the user has finished working with an assigned device, he
should use the RELEASE command to terminate the assignment
and allow other users access to the device. (When a user logs out
of the system, any devices still assigned to him are automatically
released.) A particular device is released when the user enters
the RELEASE command, a space, and the device designator (and
unit number if required), as shown below:

.RELEASE R
.RELEASE D 3

In the previous example, the high-speed reader and DECtape
unit 3 are released. The Monitor prints a dot on the next line if
the release is accomplished; otherwise, it prints a message. If, for
example, a request is made to release a device which has not been
assigned to the issuing console, the following happens:
.RELEASE D 2
ILLEGA L REQUEST

•

The Monitor printed ILLEGAL REQUEST after it checked and
found that the specified device was not assigned to the console
issuing the command.

NOTE
All commands must be formatted properJy;
ILLEGAL REQUEST is printed if the user
fails to separate the device designator and
unit number with a space.
9-15

When multiple device units were reserved by a user, each must
be individually released. For example:
.RELEASE D 1
.RELEASE D 2
.RELEASE R

•

The Monitor does not perform checking when releasing a device
as it does when assigning a device. The user may have two device
units (e.g., two DECtape units) assigned and Monitor would not
know which to release; therefore, device numbers are necessary
with a RELEASE command. When only one unit of a specific
device (one high-speed reader or punch, etc.) is on the system,
the device designator alone is sufficient.
Error Messages
An appropriate error message is printed whenever:, a Mon,itor
command cannot be perf01med at the time it is requsted, a typing
error is made, or the command is illegal (or nonexistent). Following. each error message, the Monitor ignores the command and
prints another dot, after which the user can issue another command. Table 9-2 is a list of the Monitor error messages.
Table 9-2.

Monitor Error Messages

Message

Explanation

The System Interpreter does not
understand the command. S 1 =
command.

The user attempted to use a console which is not logged into the
system.

UNAUTHORIZED ACCOUNT

Tile user attempted to log into the
system with an invalid account
number or password.

ALREADY LOGGED IN?

The user tried to log in on a console which is already in use.

FULL

The system is full. Another user
cannot log in until one of the present users logs out.
/

9-16

Table 9-2 (Cont.).

Monitor Error Messages

Message

Explanation

TYPE tBS FIRST

The user attempted to use a sys·,
tern command which cannot pres·
ently be honored due to the status
of the user's program. The message
may appear even after the user has
. typed tBS, since his program may
continue until the 110 in progress.
at the time of the halt is completed.
The user should wait a few seconds.
and then type his command a sec·,
ond time.

ILLEGAL REQUEST

The user requested an illegal com·,
mand. This error usually results
when some parameter has been
given an incorrect value or' th(;:
request refers to a facility not
owned by the user.

BUSY

The user attempted to talk to a
console which is currently print··
jng or on which another user IS
typing.

SYSTEM LIBRARY PROGRAMS
The System Library contains a comprehensive set of user pro·
grams for a wide range of applications. Language processors, such
as BASIC and FOCAL, allow the user to code and run programs.
in interactive languages. FORTRAN-D compiles and executes
programs written in FORTRAN language. A complete assembly
language system allows programs to be written in PAL-D, assem··
bled, and run. Various utility programs perform special functions .
The DEC-supplied System Library consists of the following pro··
grams.
• BASIC-an easily learned interactive language originally
developed at Dartmouth College.
• FOCAL-DEC's own interactive language for on-line
problem solving, designed especially for use on minicomputers.
9-17

• FORTRAN-D-a modified version of FORTRAN II.
• EDIT-a line-oriented text editor, used to create and
modify source programs (such as FORTRAN) and data.
files.
• P AL-D-a 2-pass symbolic assembler.
• LOADER-a binary loader used to load assembled programs for execution.
• ODT-Octal Debugging Technique for testing and modifying assembly language programs.
• PIP-Peripheral Interchange Program for transferring
files between the system disk and paper tape.
.. COPY-a utility program used to transfer files between
the system disk and DECtape.
• CAT-used to list all the files which a user has stored in
his library.
• SYSTAT-(System Status) a utility program that prints
a brief description of the system status.
A more detailed description of each of the above System Library
Programs is presented in the following sections.

General' File Characteristics
A fundamental feature of the Monitor is its ability to save programs or other data for each user in his own private library. These
individual user libraries are maintained on the system disk. Individual entries in the library are called files, whether they contain
programs or data. Within the library itself, there is no distinction
between types of files by their contents. Each file is identified with
a file name by which it is known ~nd called into use.
The user does not directly create and update the files in his library. He uses the System Library Programs for this purpose. For
example, he can use the SAVE command in BASIC. The SAVE
command takes the BASIC program named and saves it as a file
in the user's library for future use. Similarly, EDIT can be used
to modify an existing file, resulting in the creation of a new file ..
Therefore, although the Monitor provides the actual file storage
capability, most file 'manipulation is done while System Library
Programs are being run.
The System Library Programs which operate on these files must
know which file to use, when to create a new file, and what to call .
it. Each Library Program has its own method of determining
9-18

whether a user wishes to use an old file or create a new one; this
is explained in the sections on individual library programs.
Example 1:
.R BASIC
NEW OR OLD--OLD
OLD PROGRAM NAME--PRIME
READY

Example 2:
.R FORT
INPUT,TYPE
QUTPUT:BTYPE

For most of his work, the user requires access to only his own
library. However, it is often a useful feature to be able to obtain
a program from another user's library, allowing a single file to be
shared by several users. To access a program from another user's
library, the user must tell the system in which individual library
the file is stored. The user tells the system by entering the account
number of the library's owner. (In the absence of an account
number, the user's own library is the assumed source.) To get a
file from the System Library, type an asterisk immediately after
the file name.
Example 1:
.R SASIC
NEW OR OLD--OLD
OLD PROGRAM NAME--HOSSR*
READY

Example 2:
.R PALO
INPUT:NOTPIP
OUTPUTIBINI

544~

NOTE
Most examples in the discussions of individual System Library Programs use file
names within the user's own library. The
user is free (file protect permitting) to use
files from other user's libraries.
9-19

Access to another user's files is gained only with his permission.
A user may "protect" his files against other users, i.e., prevent
them from gaining access to his files, eve_n' though they know his
program name and account number. Library Programs never permit a user to write in another user's files.- Specifying a file which
is' protected, or specifying a nonexistent file, is an error that is
detected immediately. An error message is printed and the file
name is requested again.
The user places his output in a single file; however, it is often
useful to input several files together. (For example, the user may
wish to assemble two parts of a PAL-D program together.) To
specify more than one input file, separate the file names by com-'
mas. No Library Program allows more than three input files.
FORTRAN is limited to two; BASIC allows only one.
BASIC is a self-contained programming system, with an editor,
compiler, and run-time system. It also has a distinctive file format.
Files created by BASIC are not compatible with files created by
other Library Programs. All other Library Programs depend on
each other; therefore, all other Library Programs use the same
format for their disk files. Consequently, files created by the
Editor can be used as input to PAL-D or FORTRAN-D, and
numerical files created with the use of the Editor can be read by
FORTRAN programs as data files.
Up to this point, only files that exist within the time-sharing
system, i.e., on the system disk, have been described; however,
EduSystem 50 provides two othe~ means of file storage: paper
tape and DECtape. The Library Program PIP can be used to transfer files between paper tape and disk. The Library Program
COpy allows files to be transferred between disk and DECtape.

Controlling the Execution of System Library Programs
EduSystem 50 provides the user with two options for stopping
the system. CTRL/C (C with the CTRL key held down) allows
the user to stop his BASIC program and return to the beginning
of that program without returning to the Monitor. For example, if
the user begins to run a BASIC program that has an endless loop,
he can type CTRL/C to stop it. BASIC responds to tC wi\h
READY. All other Library Programs respond in a similar manner.
CTRL/B is used to stop the Library Program most recently
9-20

called. CTRL/B fo11owed by S and the RETURN key unconditionally rcturns the user to the Monitor mode; the user can then
call anothcr Library Program. If the system is printing, two
CTRL/B's and the S (tRiBS) arc required to stop the system.
RUBOUT is another useful character that deletes the la.st typed
character. Some Library Programs respond by printing '" or +while others print the deleted character. If the RUBOUT key is
typed while entering file names for input or output to a Library
Program, RUBOUT deletcs the whole line. The request for input
or output is then rcpeatcd.

Returning to the Monitor
The user can stop the execution of a System Library Program
at any time by typing CTRL/B followed by S and the RETURN
key. The System Library Programs can also initiate a return to
the Monitor. When the System 'Library Programs initiate a return, tBS is printed just as though the user had terminated the
program. For example, BASIC returns to the Monitor when the
user types the BYE command:

READY
BYE
1'85

FORTRAN returns to the Monitor after completing execution of
a program. CAT and SYST AT rcturn afer printing their particular
data output. PAL-D returns aftcr complction of an assembly,
LOADER at the end of a normal load, and EDIT after completion of an EDIT. FOCAL, BASIC, ODT, PIP, and COpy
never return to the Monitor; these programs must be tcrminated
by the user with CTRL/B and S. Somc System Library Programs
return to the Monitor when a fatal error condition is dctected.

9-21

9-22

BASIC
EduSystem 50 BASIC is a time-sharing version of the BASIC
language. It allows even the beginning computer user to write
and run meaningful programs. In addition, EduSystem 50 BASIC
has advanced language features such as strings, files, and program
chaining. This section describes the BASIC language capabilities
not discussed in Chapter 1. llable 9-6 contains a complete summary of the EduSystem 50 BASIC language.
To call BASIC, the user types:
.R BASIC

After the user logs into EduSystem 50, and calls BASIC in the
above manner, BASIC prints NEW OR OLD-. The user then
types the appropriate adjective: NEW (if he wants to enter a new
program) or OLD (if he wants to retrieve a program that was
previously filed) .
BASIC then asks NEW PROGRAM NAME-· (or OLD PROGRAM NAME-) and the user types any combination of six
letters or less. If the user is recalling an old program file from the
disk, he must use exactly the same name as when he originally
.
instructed BASIC to save it.
BASIC prints READY to signal the start of the editing phase;
the user then begins to type the new program. If the user types
a line consisting of only a line number followed by the. RETURN
key, that line is d€1eted. Each line must begin with a line number greater than 0 and less than 2047 and which contains no nondigit characters. To enter an entire line to the computer, the user
must press the RETURN key.
If the user makes a typing error while typing a statement and
notices it immediately, he can correct it by typing the RUBOUT
key (right-hand side of the keyboard), or the back arrow key
(SHIFT /0). Typing either key deletes the character in the preceding space and prints a back arrow (Ie

INT(ABS(X))

ON GOTO Statement
The ON .. ; GOTO statement may be used to provide a manyway branch. The general form of the ON ... GOTO is:

On expression GOTO line number, line number . . . .
If the value of the integer part of the expression is 1, a GOTO is
performed to the first statement. If the value of the integer part of
the expression is 2, a GOTO to the second statement number is
performed, etc .. If the value is less than one, or greater than th.e
number of statement numbers, the program terminates and an
error message is printed. Examples of ON GOTO are shown
below:

SLEEP Statement
The SLEEP statement causes a BASIC program to pause for a
specified interval, then continue running. SLEEP is followed by
the number of seconds the program is to pause. For example:
222 SLEEP 30

or
9-24

LET N=15
222 SLEEP 2*N

22~

causes a 30 second delay in the program.
The SLEEP statement is a useful way for a program to wait
for a>device (DECtape or line printer) which is busy. The ELSE
clause in the OPEN statement can go to a routine which pauses
for a while, then retries the OPEN. When the current user finishes
with the device and releases it, the program may then proceed to
OPEN and use it. This capability is especially useful when many
users may be looking up information on a single DEC tape file. It
may also be used to allow two programs to communicate with each
other. Each writes information on a tape file for the other, or
others, to read.
SLEEP should always be used when waiting for a device. While
the program is sleeping it i~ not using any processor time. A SLEEP
time of 30.to 60 seconds is recommended. It is particularly important that the program not wait by repetitively retrying the
OPEN. To do so wastes computer time' and slows down other
users. The integer, part of the argument is used to determine the
number of seconds to delay. This value must be between o and
4095.

Comments
An entire statement of comments may be included in the BASIC
program by means of the REM statement. Often comments are
easier to read if they are placed on the same line with an executable
., statement rather than in a separate REMARK statement. This
can be accomplished by ending an executable statement with an
apostrophe. Everything to the right of the apostrophe up to the
statement terminator (carriage return or backslash) is ignored
(unless the apostrophe occurs within a print literal or string
constant.) For example:
10 LET X=Y 'THIS ISA COMMENT'
PRINT "BUT THIS IS NOT A COMMENT"
3A LET X$="A'B"
2~

Thus, a comment is added to line 10 with an apostrophe, but in
lines 20 and 30 the apostrophe is treated as a valid character.
9-25

Blank Lines
To make BASIC programs easier to read, blank lines can be
inserted anywhere in a BASIC program. These can be used to
break a program into logical sections, or (as is often done) to
. insert ren1arks with the apostrophe feature. For example:
I~

'PROGRAM WRITTEN BY SAM JONES

100

Note that to insert a blank line, you must type one or more spaces
after the line number; typing the line number alone will just delete that line from the program.
Multiple Statements per Line
As many statements as will fit may be typed on a single program line~ E~ch statement must be separated by the backslash
character ""-" (SHIFT /L) . The only statement requiring a line
number is the initial one. For example:
I"" FOR 1=1 "TO 10\PRINT I\NEXT I

Note that the backslash character acts as a statement terminator
and thus cannot be included in a comment statement.
Editing BASIC Statements
If a program line is incorrect, it can be corrected by retyping
it. Minor errors in statements can be corrected by using the EDIT
command. The user types EDIT followed by the line number of
the statement to be edited. BASIC responds by printing a left
bracket ([). The user then types a search character. BASIC prints
a close bracket and prints the statement through the first occurrence of the specified search character. The user may then:
1. Type new characters which are inserted at that point
in the statement.
2. Type one or more back arrows (~) to delete characters
to the left of the search ·character.
3. Type the ALT MODE key to delete the entire line up
to that point (but not the line number).
4. Type CTRL/L to continue to the next occurrence of the
search character.
9-26

5. Type CTRL/G to specify a new search character.
6. Type LINE FEED to finish the edit, keeping the remainder of the line unchanged.
7. Type RETURN to finish the edit, deleting the remainder
of the line.
Saving Compiled Programs

BASIC compiles the current program each time it is run. If,
however, a program will be used frequently without being changed,
it may be stored in its compiled form. A compiled program can
be retrieved and executed faster than a BASIC source program.
To save a compiled program, the user types:

COMPILE FAME

The program is saved on the disk under the specified name
(FAME). If a file by that name exists, BASIC prints DUPLICATE FILE NAME and does not compile that program,
Once a program has been compiled, it may be retrieved and
run just like an ordinary BASIC source program. It may not,however, be listed, saved, or changed. If an attempt is made to do
any of these things, the message EXECUTE ONLY is printed.
The compile capability may therefore be used to protect programs
from unauthorized listing or changing. Since only BASIC source
programs can be edited, the user may wish to store both a source
and a compiled version of a given program.
Compiled files are distinguished from regular BASIC programs
by their file extensions. BASIC source programs have an extension of .BAS. Compiled files have an extension of .BAC. These
extensions are printed along with the flle name when a catalog
is requested.
File Protection

EduSystem 50 permits a user to specify a protection code for
each file. (See the section on Advanced Monitor Commands for
a full description of protection codes.) The commands which write
disk files (SAVE, REPLACE, COMPILE) also permit the user'
to specify what protection is to be given to a file. This is done
9-27

by following the file name with the protection code
brackets. For example:

angle

SAVE DEMO < lei>

will create and save a file named DEMO.BAS having a protection
code of 10. When no prot~ction is specified, a protection of 12 is
automatically assumed.

Project-Programmer Numbers
In specifying the Account Number prior to requesting an OLD
file, the user may optionally type a Project-Programmer number
(giving the Account Number as two 2-digit numbers separated
by commas instead of a single 4-digit number). In this way, the
user may RUN files from another user's disk area. For example,
both of the following are acceptable:
OLD PROGRAM NAME--FILE 13,3

where 13 is the Project Number and 3 is the Progtammer Number, or:
OLD PROGRAM NAME--FILE 1303

where 1303 is the account number. The two file name indications
are equivalent.
Restricted Accounts
As an added system protection, BASIC checks to see if an
attempt is being made .to run BASIC under Accounts 1 or 2. If so,
BASIC prints the error message:
IMPROPER ACCOUNT
ABORT
tBS

thus preventing BASIC from interfering with the System Directories or the System Libr~ry.
9-28

Catalog Format

The CATALOG command prints file names and file extensions,
file size, and file protection codes for the specified account (the ac-'
count under which the user logged into the system). For example:
CATALOG
NAME
SIZE PROT
TEMPeJ0
1
12
BASeJ00.TMP
1
17
BASI00.TMP
1
1 '1
IBOLD .BAC
12
DEMO
.BAS
10

Strings in BASIC
EduSystem 50 BASIC has the ability to manipulate alphabetic
information (or strings). A string is a sequence of characters,
each of which is a printing ASCII character (see Appendix B).
EduSystem 50 strings consist of one to six characters; strings of
more than six characters are truncated on input to six characters.
Variables can be introduced for simple strings, string arrays, and
string matrices. A string variable is denoted by following the variable name with the dollar sign character ($). For example:

Al$
V$(7)
M$(1,l)

A simple string of up to six characters.
The seventh strin~ in the array V$(n).
An element of a string matrix M$ (n,lll) .

When string arrays or matrices are used, a DIM statement is
required. For example:

reserves space for eleven 6:-character strings for the array V$, and
space for 36 6-character strings for the matrix M$.
READING STRING DATA
Strings of characters may· be read into string variables from
DATA statements. Each string data element is a string of one to
six characters enclosed in quotation marks. The quotation marks
are not part of the actual string. For example:
10 READ A$IB$IC$
200 DATA "JONJ::S"I"SMITH"I"HOWE"

9-29

The string JONES is read into A$, SMITH into B$, and HOWE
into C$. If the string contains more than six characters, the excess characters are ignored. The following program:
10 READ A$
20 PRINT A$
30 DATA "TIME-SHARIN.G"
40 END
RUN

causes only
TIME-S

to be printed.
String and numeric elements may be intermixed in DATA
statements. A READ operation always fetches the next element
of the appropriate type. In the followi!lgexample:

10 READ AIA$IB
20 DATA "YES"12.5 1 "NO"11

2.5 is read into A, YES into A$, and 1 into B.
The standard RESTORE statement (as described in Chapter 1 )
resets the data pointers for both string and numeric elements. Two
special forms of the RESTORE command, RESTORE* and
RESTORE$, may be used to reset just the numeric or string data
list pointers, respectively. For example:
10 READ AIA$IH
20 DATA "YES"12.51"NO"11
30 PRINT AIA$IB
40 RESTORE*
50 READ A1A$IB
60 PRINT AIA$IB
70 END

RUN

would print:
• 2.5
2.5

YES
:\10

9-30

If line 40 -Were changed to RESTORE, this program would print:
YES
YES

since the numeric as well as string data lists would be reset.
PRINTING STRINGS
The. BASIC PRINT statement ~ay be used to print string information. If the semicolon character is used to separate string
variables in a PRINT command, the strings are printed with no
intervening spaces. For example, the program:
10 READ A$IB$IC$
20 PRINT C$JB$JA$
30 DATA ,"ING"I "SHAR"I "TIME-"
40 END

causes the following to be printed:
TIME- SHARING

INPUTTING STRINGS
String information may be entered into a BASIC program by
means of the INPUT command. Strings typed at the keyboard
may contain any of the standard ASCII characters on the user terminal except back arrow (<<-) and quotation mark ("). Back
arrow is used in BASIC to delete the last character typed. Commas are used as terminators just as with numeric input. If a string
contains a comma, the entire string must be enclosed in quotation marks. The following program demonstrates string input.
10 INPUT A$IB$IC$
20 PRINT C$IB$IA$
30 END
RUN

? JONES1SMITH1HOWE
HOWE
SMITH

JONES

READY

Strings and numeric information may be combined in the same
INPUT statement as in the following example. Note that if an
9-31

input str~ng contains 'more than six characters, only the first six
are retained.
10 INPUT A"A$"B$
20 PRINT A$"B$"A
30 END
RUN
? 01754"MAYNARD" MASS.
MAYNAR
MASS.

1754

The numeric variable A is set to 1754 (leading zeros are deleted), the string MAYNAR is put in the string variable A$,and
the string MASS. is put into the string variable B$. To print the
number 01754, the number could be input and output as a character string.
LINE INPUT
Strings of more than six characters may be entered by means
of the LINPUT (line input) statement. A LINPUT statement is
followed by one or more string variables. For example:

The first six characters to be typed are stored in the first string
variable, the next six in the second, and so until the line of input
is terminated by a carriage return.
Commas and quotes are treated as ordinary characters and
hence are stored in the string variables. For example, if the following line were typed in response to the above LINPUT command:
?MAYNARD" MASS.

01754

then the values of the string variables would be as follows:
A$ (1) = "MAYNAR"
A$(2j = "D, MAS"
A$(3) = "s. 017"
A$( 4) = "54"
A$ ( 6) = " "1
1.

Strings may consist of zero characters. Such a string is empty (or null).

If printed, it causes nothing to be output. The null string is usually repre-

sented by a pair of- quotes with nothing between (""). The null string
should not be confused with" a string of one or more spaces.

9-32

In the above example, the maximum number of characters
which could be typed would be 30. Any additional chara~ters would
be ignored. In all cases, the maximum number of characters
which may be typed in response to LIN PUT is 50. If a longer line
is typed, the message LINE TOO LONG is printed. The input
line is ignored and must be reentered.
It is possible to mix numeric and string variables in a LINPUT
statement, but this practice is not recommended. As an illustration
of how this might be done, consider the example given earlier:

where the user might type:
? 01754 1 MAYNARDI MA

This still sets the numeric variable A to 1754 (when used in
LIN PUT statements, numeric input remains unchanged). However, the string variable A$ would now be MAYNAR, and the
.
.
string variable B$ would be D, MA.
When inputting strings with LINPUT, the error messages: MORE?
and TOO MUCH INPUT, EXCESS IGNORED cannot occur.
WORKING WITH ·STRINGS
Strings may be used in both LET and IF statements. For
example:
10 LET Y$="YES"
20 IF Z$="NO" THEN

100

The first statement stores the string YES in the string variable Y$.
The second branches to statement 100 if Z$ contains the string
NO. For two strings to be equal, they must contain the same
characters in the same order and be the same length. In particular,
trailing blanks are significant since they change the length of the
string. "YES" is not equal to "YES ".
The relational operators < and> may also be used with string
variables. When used with strings. these operators mean "earlier
in alphabetic order" or "later in alphabetic order", respectively.

9-33

They may be used to alphabetize a list of strings, for example ..
The relation operators >=, <=, and <> may be used in a similar
manner. The arithmetic operations (+, -, *, /, t) are not defined
for strings. Thus, statements such as LET A$ = 3:1< 5 and LET
C$ = A$+ B$ have no meaning, and should not be used in a
BASIC program. They will not cause a .diagnostic to be printed;
however, the results of such operations are undefined.
THE CHANGE STATEMENT
The CHANGE statement may be used to access and alter individual characters within a string. Every string character has~ a
numeric ASCII code (see Appendix B), a number which is used
to indicate that particular character. The CHANGE statement
converts a string into an array of numbers, or vice versa; The
CHANGE statement has the form:
100 CHANGE A TO A$

or
100 CHANGE A$ TO A

where A$ is any string variable (or an element of a subscripted
string variable) and A is an array variable with at least six elements. Any array variables used in CHANGE statements must
have appeared ina DIM statement with a dimension of at least
SIX.

The following program illustrates the use of the CHANGE
statement by changing a string variable into an array of numbers.
10 DIM A(6)
20 READ A$
30 CHANGE A$ TO A
40 PRINT A(0)JA(1)JA(2)JA(3)JA(4)JA(5)JA(6)
50 DATA "ABCD)
50 DATA "ABCD"
60 END
RUN
4

The CHANGE statement takes each character of the string and
stores its corresponding numeric (ASCII) code in elements one to
six of the array. Remaining array elements are -set to zero. The

9-34

length of the string (0-6 characters) is stored in the zero element
of the array. In the example above, the character codes for A~
B, C, and D are stored in A(1) to A( 4). A(5) and A( 6) are set
to zero. The number 4 is stored in A (0) since the string A$ is
four characters long.
.
CHANGE may also be used to change an array of numeric:
codes into a character string as in the following program:
10 DIM A(6)
20 FOR I=~ TU 5
30 READ A( I)
40 NEXT

50 CHANGE A TO A$
60 PH INT A$

70 DATA
80 END

5169~6818515314H

RUN
EDU50

The length of the resulting string is determined by the zero e1e··
ment of the array. In the previous example, the string is five char··
acters long. The elements of the array, starting at subscript 1, are:
assumed to be numeric character codes; these are converted to
characters and are stored in the string. If any codes encountered'
are not valid character codes, or if an invalid string length is
given, the message BAD VALUE IN CHANGE STATEMENT
AT LINE n is printed, and execution is stopped.
A BASIC string of less than six characters always has the remaining character positions filled with zeros. For this reason,
when such a string is changed to an array, the first six array elements are set to zero. The CHANGE statement always fills six
array elements, even though the strings may not be six characters
long. The user should be careful to dimension the array used in a
CHANGE statement to at least six. If a string of characters is
transformed into an array of less than six elements, an undetected
error will occur.
The CHANGE statement is usable with strings not created by
BASIC. It may, for example, be used to access files other than
BASIC data files. Each string variable corresponds to three PDP-8
words. The CHANGE statement treats these three words as six
6-bit bytes, converts each 6-bit byte to its numeric character code
equivalent and stores it in the corresponding array element. The
9-35

zero element of the array, the string length; is set equal to the
number of bytes (characters) before the first zero byte. When reading unspecified data, there may be non-zero bytes following
this zero byte. If so, they will be transferred to the array as ,~ell.
THE CHR$ FUNCTION
Occasionally, it is desirable to type a character other than
those in the printing ASCII set, or to compute the value of a
character to be printed. For this purpose, the CHR$ function can
be used in a PRINT statement. The argument of the CHR$ function is sent as an ASCII character to the Teletype'. For example:
10 FOR 1=121 TO 9
2121 PRINT CHR$(1+48);
30 NEXT I
40 END

prints 0123456789, since 48 to 57 are the ASCII values for the
characters 0 to 9. The following special characters can also be
printed using the CHR$ function:
Bell
-Line feed
Carriage return
Quote (")
Back arrow (~)
Form feed

CHR$ (7)
CHR$ ( 10)
CHR$ ( 13 )
CHR$ (34)
CHR$(95)
CHR$(12)

The Teletype will accept characters from 0 to 255 (decimal),
many of which do nothing on most kinds of teletypes. Some of
the special (non-printing) characters should not be used. For example, CHR$ ( 4) causes a Dataphone to disconnect.
For each ASCII code there is a second acceptable form permitted in CHANGE and CHR$. The second code is obtained by
adding 128 to the code given in the table in Appendix B. For example, CHR$ would type A in response to either 65 or 193 as
an argument.
Program Chaining

Most programs are easily accommodated by EduSystem 50
BASIC. If a program becomes very long, however, it may be
necessary to break it into several segments. Typ~cally, programs of
more than two to three hundred statements must be split into more
9-36

than one file. A program that has been broken into more than
one piece is commonly called a chained program.
Each part of a chained program is saved on the disk as a separate file. The last statement of each part to be executed is a
CHAIN statement specifying the name of the next part of the
program. The next file is then loaded and executed. It may in turn
chain to still another part of the program. The general form of
the chain command is:
414 CHAIN "NAM E"

or
414 CHAIN Ai

where NAME is the name
to six characters enclosed
next segment may also be
case, the file of that name

of the next segment to be executed (one
in quotation marks). The name of the
contained in a string variable. In either
is loaded and run. Thus, the statement:

999 CHAIN "SEG2"

is eq uivalent to:
OLD
OLD PROGRAM NAME--SEG2
RUN

except that it happens automatically. Each separate part of the
program automatically links to the next part of the program chain.
The individual sections of a chained program may be either
regular source files (.BAS) or compiled files (.BAC). If the sec-·
tions arc source files, they must be compiled before they are runo
A chained program runs more efficiently if all its sections have
been compiled. Source and compiled files cannot be mixed in
program files.
If an error occurs while compiling or running a chained pro-gram, the name of the section containing the error is printed as

9-37

part of the error message. In all cases, whether a program terminates by an error or a STOP or END, BASIC returns to the
first program in the chain. This is the one which is available for
.editing and rerunning when BASIC prints READY.
Most chained programs require that information from one section be passed to the next. The first section may, for example,
accept input values and perform some preliminary calculations. The
intermediate results must then be passed to the next section of
the programs. This p~ssing· of values is done by means of data
files which are explained in tbe next section. Whenever a CHAIN
operation is performed, program data which has not oeen saved
in a file is lost. Variable and array values are not automatically
passed to the next program.

Disk Data Files
The standard BASIC language provides two ways of handling
program data items. They may be stored within the program (in
OAT A ·stater,nents) or they may.be typed from the terminal. OAT A
statements, however, allow for only a limited amount of data.
Also, the data is accessible only to the program in which it is em- .
bedded. Typing data from the terminal allows it to be entered
into any program, but this is a time-consuming process. In either
case, the data or results of calculations cannot be cOliveniently
stored for future use. All these limitations m'ay be overcome by the
use of disk data files.
A data f)·le is separate from the program or programs which
use it. It is a file on the disk similar to a saved program, but it .
contains numbers or strings rather than program statements.
This information may be read or written by a BASIC program.
( I nformation in a data file is stored in a coded format; therefore,
it cannot be listed by the BASIC Editor or EDIT.) (The maximum
size of a data file is about 350,000 characters.) String and numeric information may be combined in a single data file. The number of data tllcs a user may have is limited to about 100, space
allowing. When a file is first created, its contents are undefined.
FILE RECORDS
A data file is made up of logical units called records. A record
may be as small as a single numeric or string variable. More typically, it is a group of variables or arrays. The design of the program lIsually dictates the most efficient size of the record. If, for

·9-38

example, the program manipulates a series of 5 by 5 matrices,
each record could contain one such matrix. If the program operates on 80-character alphanumeric records, 14 string variables
might comprise a record.
The size and composition of a record are defined with a
RECORD statement. Like the DIM statement,RECORD is followed by a series of variables. They may, however, be unsubscripted as well as subscripted. For example:

10 RECORD A(S"S>
10 RECORD B$(14)
10 RECORD A,,B,,C$(8),,D,,E(S>

J:he set of variables mentioned in a RECORD statement, taken
together, constitute a record. Each element within the :record is a
field. Numeric and string information may be mixed to comprise a
more convenient record.
Variables mentioned in a RECORD statement should not appear
in a DIM statement. 'The RECORD statement reserves variable
space exactly as a DIM statements does. The difference is that the
variables are also identified as being used for file Input and output.
Non-subscripted variables appearing in RECORD statements must
not have been used previously in a program; therefore RECORD
statements should always be the first statements in a program.
Records may be any length. A long record is typically more efficient since more information is transferred in a single operation.
Records should, however, be only as long as necessary since excess
variables lengthen the file. In particular, it is important to remember that all arrays and matrices have zero elements. The array
A(5,5) has 36 elements, not 25. If A appears as part of a record,
all 36 elements should be used.
It is also useful to try to make record sizes 43 variables long,
or a multiple of 43. Each RECORD statement reserves program
variable space in units of 43 whether or not the record is that big.
Unless the record fills this area, some program variable space is
wasted. It is not worthwhile, however, to make an inherently small
record 43 variables long just to conform to this convention; this
would make the file unnecessarily large.
9-39

OPENING A DISK FILE
Disk data files are completely separate from the programs
which use them. Therefore, the program must specify which file or
files it will use. The OPEN command is used for this purpose.
OPENing a disk data file associates it with an internal file number, either 8 or 9. (A program may have two disk data files open
at one time.) For example:
100 OPEN 9 .. "DATA10"
11210 OPEN 8 .. A$

The name of the file to be opened may be explicitly stated in the
OPEN commpnd. If i,t is, it must be contained in quotation marks.
The file name may also be .contained in a string variable, allowing
the program to decide which file to open, perhaps on the basis
of input from the program's user. In either case, the name of the
file is preceded by the internal file number, either 8 or 9. This
argument may also be an expression whose value is either 8 or 9.
When a file is opened on an internal file ,number which has a
file already open, the previously opened file is closed and the new
file opened.
•
If no file of that name exists, the file is created. In .either case,
once the file is open, it is available for both reading and writing.
BASIC disk data files are assigned an extension of .DAT which
need not be spes}fied as part of the file name in the OPEN statement.
READING/WRITING DISK FILES
Once open, files may be read and written, one record at a time,
using the G~T and PUT statements. GET statements read one
record of information directly into the variable in the RECORD
statement. PUT statements write the present values of the variables
in the RECORD statement. Both GET and PUT statements are
followed by the internal file number (8 or 9 or an expression),
the line number of the RECORD statement 'containing the variables to be transferred, and the name of a control variable. For
example:
100
110
120
130

RECORD A .. B .. C$(30)"D(8)
OPEN 8" "FILE1"
LET 1=0
GET 8 .. 100 .. 1

9-40

The control variable specifics the file record to be transferred.
I n the example above, Fl LE 1 is opened as internal file 8. The
value of the control variable, L is zero. The GET statement in
Ii ne 130 reads the first record (record ()) of FI LE I into A, B,
and the arrays ('$ and D. Single nlimeric values arc read into A
and B, 3 I strings arc read in C$, and 9 numeric values are read
into D. After each transfer, whether it is a GET or a PUT, -the
value of the control variable is automatically incremented. Successive GET's or PUT's automatically proceed to the next record
of the file.
The PUT statement has a similar format. For example, if line
130 or the preceding program had been:
C

130 PUT

8~100~I

the present values of A, B. C$, and D would have been written
to the first record of FI LE I.
File records may be accessed randomly by setting the control
variable to the desired record number before doing the GET or
PUT. Single records may be read. changed. and then written with,out proces_sing the entire lile. When reading a file, the record referenced in the GET statement must. of course, be the same as
the record referenced in the PUT statement which- wrote the data
onto the file. The total length of the record and the relationship
of string and numeric fields within the records used for the GET's
and PUT's must be the same. If they arc not. improper information will be read and written.
New files may be created by openiri'g a file which docs not
alreadv. exist. As successive records are- written onto the file. its
length is extended as necessarv.
. When a new file is created. it is
usct"ul to immediately write an end-of-file code in the last record.
W.riting the last recl)rd first forces the entire file to be allocated.
making sure that enough disk space is available. It also provides an
end-or-file mark. Programs which read this file may. then check
for this end-or-file mark to avoid readil~g past the end of the data
file which results in an error. .
Existing flies may be enlarged by writing a new record farther
out. If the program do~s not know how big the file will be. it may
simply write records to the file in sequcncc.
-

9-41

The file will be automatically ex~ended. When all the records have
been written, one final end-of-file mark can be added.
In general,all records read or written on a specific file should
be the same length, i.e., contain the same number of variables.
However, if the user is careful he may intermix records of different lengths in a file. Suppose the following statement is executed:
40 PUT 8 .. 100 .. N

and the value of N is n and the record specified by statement 100
is of length m. The PUT statement will write m variables in the
file starting at the m*n variable. The simple rule for computing
the first variable in the .file to' be accessed is the record length
times the record number" (Remember the first record is record
number zero.)
c

CLOSING/DELETING DISK FILES
When all work has be~ncompleted on a data file, it should be
closed with a CLOSE statement. Once the file is closed, it may
not be read or written unless it is reopened. The file does, however, remain on the disk and is available for future use. The
CLOSE statement is followed by the interna,l file number to be
closed (B or 9). For example:
950 CLOSE 8

If the 'disk file was just created for temporary' scratch use (to
pass parameters during a CHAIN, for example), it should be
deleted at the end of the program instead of closed. The UNSA VE
statement is used to delete files. For example:

The file opened on internal file number 9 is deleted from the disk.
Both CLOSE and UNSAVE may ,be followed by an expression
e.quating to 8 or 9 instead of a constant.
Open disk data files are automatically closed at the end of the
program, unless the program CHAINs to another program. In this
case, all open files remain open and the new program may access
them without executing an OPEN statement.
9-42'

DECtape Data Files
Large permanent data files are best stored on DECtape rather
than on disk. Each DECtape holds up to 380,000 characters of
information. DECtape data files may be dismounted for safekeeping, thereby insuring their privacy. Data files on DEC tape
are similar to files on disk except that they do NOT have filenames.
Each reel of DECtape is treated as a discrete data file. When the
tape is mounted on a DECtape drive, records may be read and
. written *ectly onto the tape.
A D~tape data file may be used by only one user at a time.
Once a DECtape unit is assigned, a single user has exclusive
access to it until he releases it. Each DECtape drive has a WRITE
LOCK switch which physically prevents any write operations to
that unit. If the WRITE LOCK switch is set, programs may not
write on the tape even if the unit is assigned.
DECtape data files may be used in a variety of ways. Programs
which need large data files should use DECtape to avoid consuming large disk areas. Administrative files, such as student or
employee records, are best stored on DECtape. Since they are
removable and can be write-locked when mounted, their use can
be tightly controlled. DECtapes are also useful for information
retrieval. A data tap'e may be ~~pt permanently mounted but
write-locked. Individual users may run programs which assign and
query that file, then release it for others to use.
DECT APE FILE RECORDS
Records for DECtape data files are specified the same way as
for disk data files: with a RECORD statement. All rules for disk
records apply to DECtape records. In fact, the same RECORD
statement may be used for both a DECtape and disk file .. (This.
is useful when transferring a tape file to a disk file for processing.
Access to disk data files is considerably faster than to DECtape
data files.)
it is possible to specify any record length for a DECtape data
file, but a size of 43 -variables is' suggested, even more strongly
than for'disk data files. DECtapes are physically structured into
blocks, each of which holds exactly 43 variables. If the record
specified by the program is, for example, 44 variables, it requires
two full blocks on the tape.
Records which are multiples of 43 variables are efficient in
9-43

utilizing DECtape space but are not efficient in speed. Such records
are written in consecutive DECtape blocks. The tape unit cannot
read or write consecutive blocks without stopping the tape and
rewinding it slightly (rocking). This tape rocking also occurs
when single block records (43 variables or less) are read or written as consecutive DECtCl.pe records. (In this case, each DECtape
file record corresponds to a physical tape block.)
The most efficient way to utilize DECtape is to make records
43 variables in length and write them onto every tenth record in
the file (records 0, 10, 20, etc.). When the entire length of the tape
has been traversed (the last block of the tape is number 1473),
write next into records 1, 11, 21, etc. In this way, every record
is eventually filled. Programs which will be used repeatedly should
access the tape in this manner.
OPENING A DECTAPE FILE
DECtape data files, like disk files, are completely separate from
the programs which use them. Therefore, the program may specify
which tape, or tapes, it will use. The OPEN statement is used for
this purpose. Since DECtape files do not have names,2 the OPEN
statement specifies the DECtape unit number to be used. It is
assumed that the proper tape reel has been mounted. If the file
is to be updated, the uni_t shou18 be write-enabled. If not, it should
be write-locked. The OPEN statement is followed by the unit
number to be used (0-7).
100 OPEN 2
100 OPEN 7

The unit number could be an expression. Making the unit number a variable is very useful since it is hard to predict which units
will be available at the time the program is run: When the unit
specification is a variable, the user may mount the file on any
free unit, then INPUT the number into the program.
When the OPEN statement is executed, the indicated DECtape
unit is automatically assigned to the user. It cannot subsequently
be assigned to any other user. Thus, it is possible to try to open,
2 It is important to note that BASIC data file DECtapes are not the same
as the file-oriented DECtapes used by COPY. There is no directory on a
BASIC DECtape file. Each tape is considered to be one file of data.

9-44

hence assign, a unit which is already assigned. If, in the above
examples, units 2 and 7 were already assigned to the current user
or any other user, the program would be terminated arid an error
message printed.
An alternative form of the OPEN statement allows the program itself to handle this situation. OPEN statements may include
an ELSE clause which specifies a line number. If the OPEN
statement fails, BASIC automatically performs a GOTO to this
line number. For example:
100 OPEN 2 ELSE 900

If unit 2 is available, it is assigned and BASIC goes on to execute
the next statement. If unit 2 is not available, statement 900 is exe-

cuted next. Statement 900 could print a message and perhaps ask
for an alternate unit number.

READING/WRITING DECTAPE FILES
DECtape data files are read and written using the same GET and
PUT statements as are used for disk data files. The internal file
number is a number between a and 7, or an expression. Unlike
disk data files, DECtape data files are of a constant length equal
to the capacity of the tape. The exact number of records per reel
depends on the record size as follows:
Record Size

Tape Capacity

1-43 variables
44-86 variables
87-129 variables

1474 records
737 records
491 records
,

As indicated in the section on DECtape data records, a record
size of 43 variables or less is recommended since it conforms to
the physical blocking of the tapes themselves. It is also desirable
to space the records along the tape so that the tape does not waste:
time rocking. The following subroutine could be used to write:
1474 records on the tape in this fashion. It assumes that R is set
to zero before it is called the first time and that the unit number
is in U.
9-45

500
510
515
517
524
530
540
545
547
550
560

REM SUBROUTINE TO WRITE RECORDS ALONG TAPE
REM WRITES ONE RECORD EACH TIME CALLED
PUTU"10,,R 'REMEMBER THIS INCREMENTS R
LET R=R+9 'SPACE OUT 10 BLOCKS
IF R<1474 THEN 550 'OK TO RETURN
IF R=1479 THEN 560 'TAPE IS'FULL
LET R=R-1479
IF R>0 THEN 550
LET R=R+10
RETURN
STOP 'TAPE IS FULL

The following function may also be used to convert a logical
record number (0 to '1469) to a physical record block spaced
along the tape. This function does not use blocksO-3. These blocks
are, therefore, available for a header or label. Both the subroutine
above and the function below assume a record length of 43 variables or less.

FNC(X) = (X-INT(X/147)*147)*10 + INT (X/147)+4
Once opened, any record on the tape may be read. The tape
unit must, however, be write-enabled if it is to be written. Trying
to' PUT to a write-Iock.ed tape is an error.
CLOSING OECT APE FILES
Once all work on a OECtaQ.e data file has been completed it may
be closed. Closing a file releases the tape unit and makes it available to other users. Thus, if the tape contains important information
(and especially if it is write-enabled) the CLOSE should not be
done until the tape reel has been removed. If no CLOSE statement
is encountered in the program) the unit remains assigned after
the program has finished. The OECtape unit remains assigned
until a Monitor RELEASE command is executed or the user logs
out. An example of a CLOSE statement follows:
IIVl(i'J CLOSE 6

USING OECT APE OAT A FILES WITH OS/8 FORTRAN
Numeric OECtape data mes written by BASIC may be read by
OS/8 FORTRAN with the FORTRAN RT APE and WT APE
subroutines. and vice-versa. (String and Hollerith variables use
different character codes.) Thus, it is possible to use BASIC to
9-46

prepare an input or update tape for a stand-alone FORTRAN program. This provides a conyenient way to do big jobs in ofl·hours,
without having to leave the time-sharing mode for very long.
Line Printer Output
If a line printer is "available, it may be used both to list BASIC
programs and to serve as an output device for the programs
themselves. The line printer may only be used by one ,,!ser at a time.
The statements associated with line printer output are LLIST
and LPRINT.
LLIST is similar to the LIST command except that the program
listing is output to the line printer rather than to the Teletype. The
LLIST command assumes that no other user has the line printer
assigned and "responds by typing WHAT? if the line printer is not
available. After the listing is complete, the line printer is released
and is available to any user.
BASIC programs may use the line printer as an output device
during execution by means of the LPRINT statement. LPRINT is
exactly like PRINT except that the information goes to the line
printer rather than to the Teletype. All formatting conventions
of the PRINT statement are available with LPRINT. In particular,
CHR$ ( 12) may be" used to skip to the top of the next form
(page).
"
The LPRINT statemeht also assumes that no other user has the
line printer assigned. However, using this statement when the line
printer is not available causes the program to terminate. Once
LPRINT successfully assigns the line printer, it remains assigned
until the program terminates.
.
The OPEN and CLOSE statements may be used to assign and
release the line printer. An OPEN statement with a device number
of 11 assigns the line printer, or if it is not available and an ELSE
clause is specified, transfers control to the line number specified
in the EI;..SE clause. CLOSE 11 releases the line printer.
Paper Tape Output
The high-speed paper tape punch 1Jlay also be used as an output
device. Like the line printer, the paper tape punch may only be
used by one user at a time. OPEN and CLOSE statements with an
internal file number of 10 will, respectively, assign and release
the paper tape punch as shown in the following example:
9-47

10 OPEN 10 ELSE 100 'GOTO 100 IF ?UNCH UNAVAILABLE
20 CLOSE 10

Here too, a GOTO statement in combination with an ELSE clause
can be used to transfer program control if the paper tape punch
is unavailable.
The LPRINT statement causes output to the paper tape punch
when this device has been assigned. For example:
10 OPEN 10
20 LPRINT "THIS GOES TO PTP."

causes the statement THIS GOES TO PTP. to be punched onto
paper tape. If the paper tape punch is not released with a CLOSE
statement, it remains assigned after the program terminates.
Internal.Data Codes
Using the file I/O capabilities and the CHANGE statement, it
is possible to examine data which was written on a DECtape or
disk file by a program other than BASIC. There are two data formats: numeric and string.
NUMERIC DATA
Each numeric value in BASIC is three PDP-8 words long. The
storage format for numeric data is as follows:
o
WORD I
SIGN

-;--L--'-l---'------L.......--'------'----'-_ _L-.J.....---0.'----1

L-I

-.-J '-'----..:....,r~----J '---.------'t

BINARY EXPONENT
•
HIGH ORDER M A N T l S S A - - - - - - - - - - - - I

o
WORD 2

LI_______________
MANTISSA

o
WORD 3

LI.'--_____________-.--J
LOW ORDER MANTISSA

A one in the SIgn bit means that the number IS negative. The
•
exponent is kept in excess 200 form where:
200~

is 2°
201 R is 21
177 8 is 2- 1
9-48

The assumed deci~al point is be,tween bit 8 ~nd bit 9 of word ].
AlSo, the number IS always normalized, meaning that bit 9 is aJ.ways 1 unless the number is zero. (Zero is represented by thre~~
zero words.) Note that this format is the same as the fprmat used
by FORTRAN-D.

Table 9-3. 'BASIC Internal Data Codes

6-Bit
Byte

Byte

Octal

Decimal

00
01
02
03
04
05
06
97
10

0
1
2
3
4
5
6
7
8
9
10

12
13
14
15
16
17
20
21
22
23
24
25
26
27
30
31
32
33
34
35
36
37

12
13

14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31

ASCII
Char.
NULL
SPACE

#
$
%
&
.()

+
/

0
1
2
3
4
5
6
7
8
9

<
>
9-49

6-Bit
Byte

Byte

Octal

Decimal

40
41
42
43
44
45
46
47
50
51
52
53
54
55
56
57
60
61
62
63
64
65
66
67
70
71"
72
73
74
75
76
77

32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63

ASCII
Char.

?
@
A

B
C
D
E
F
G
H
I
J

K
L
M
N

0
P
Q
R
S
T
U
V

X
y
Z
[

'"
]

STRING DATA'.

DP-8 words long. Each word
Each string v~nable IS th~ee ~ers If a string .variable is filled
contains two 6-blt bytes or c. ahra
. t written by a BASIC proGET f
a source whlc . was no
by a .
romC'
ay examine the data in the variable b. Y
ram a BASI program m '
" n be
~erfO'rming a CHANGE on that variable. The SlX bytes WI
translated as if they were internal character codes for BA.SIC
string characters. Table 9-3 shows how this translation interprets
the 64 possible types. Note that after such a CHANGE, the
Oth element of the an:ay contains a count of the number of characters occurring before the first null.
Error Messages
Most programs, especially if they are at all complex do not execute correctly the first time they are tried. EduSystem 50 checks'
all BASIC statements when they are entered and before executing'
them. If it cannot execute a statement, it informs the user by printing one of the error messages shown in Table 9-4, followed by the
lihe number, if present, in which the error occurred.
In addition, the system checks for non-fatal execution errors
and notifies the user that he performed a computational range
error. When errors of this type occur, the messages shown in
Table 9-5 appear, followed by the line number in which the error
occurred.

Table 9-4.

BASIC Error Messages

Message

Explanation

WHAT?

The editor cannot understand the command given.

SYSTEM 1-0 ERROR

BASIC was unable to perform the
desired dis.k 110.

PROGRAM TOO LARGE

The program js too large to be executed. Make it smaller.

NO END STATEMENT IN
PROGRAM

All programs must have an END
statement.

ILLEGAL INSTRUCTION

A statement was used which is not
one of the legal ,BASIC statements.

9-50

Table 9-4 (Cont.).

Message

BASIC Error Messages

Explanation

ILLEGAL SYNTAX

The expression in a statement does
. not agree with the BASIC syntax.

DEF STATEMENT
MISSING

A function needing a DEF statement
exists in the program.

FOR WITHOUT NEXT

There is an unmatched FOR statement in the program.

NEXT WITHOUT FOR

The NEXT statement indicated has no
preceding FOR statement.

ILLEGAL CHARACTER

The user attempted to use an illegal character in the statement being processed.

ILLEGAL LINE NUMBER

The format of the line number being
used in a GOTO or IF statement is
not acceptable.

ILLEGAL OPERATION

The expression being processed doecs
not agree with the BASIC rules (this is
probably due to unmatched parentheses) .

STACK OVERFLOW

The user programmed a situation in
which the expression is too complicated :to be executed.

ILLEGAL CONSTANT

The format of a constant in the statement being processed is not valid.

OUT OF DATA

A~ attempt was made to READ more
data than was supplied by the user.

ILLEGAL FORMAT

The structure of the statement does
not agree with BASIC syntax.

DIMENSION TOO LARGE

Too large an array to fit in the available core.

UNDEFINED LINE
NUMBER

The line number appearing in a
GOTO or an IF-THEN statement does
not appear in the program.

BAD FILE NAME

The file name used is not valid, e.g.,
it does not begin with a letter.

9-51

Table 9-4 (Cont.).

BASIC Error Messages

Message

Explanation

SUBSCRIPT ERROR

A negative subscript was used for an
array.

MISUSED TAB

The TAB function was used in an invalid manner . TAB can appear only
in PRINT statements.

GOSUB-RETURN ERROR

Subroutines are too deeply nested or
a RETURN statement exists outside
a subroutine.

ILLEGAL FOR NESTING

FOR-NEXT loops are too deeply
nested or NEXT appears before FOR.

ILLEGAL VARIABLE

An illegal variable was used in an
array.

DISK FULL

There is no more storage space on the
system disk.

IMPROPER ACCOUNT #
ABORT
tBS

A user logged in under account numbers 1 (system account) or 2 (system
library) and tried to run BASIC. This
is prohibited.

BAD FILE FORMAT

The program specified in response to
OLD PROGRAM NAME was not
acceptable to BASIC. This is generally caused by: (1) trying to load an
obsolete compiled (.BAC) file, or (2)
trying to load a non-BASIC (FORTRAN or PAL-D) program.

MISUSE OF CHR$

The CHR$ functi~n was used in an
invalid manner. CHR$, like TAB,
can appear only in PRINT state-·
ments.

BAD VALUE IN CHANGE
STATEMENT

While performing CHANGE A TO
A$, one of the elements of the array
A was found to contain an illegal
value.

TIME LIMIT EXCEEDED

The number of statements executed
by a job has exceeded the maximum
established by the system manager.
Generally, some error was made and
the program is caught in a loop.

9-52

Table 9-4 (Cont.).

BASIC Error Messages

Message

Explanation

PROGRAM IS "progname"

This message may immediately folIowan error message, to identify the
current program ina series of
CHAINed programs. If there is no
CHAIN, this message will not occur.

PROGRAM NOT FOUND

The file which the user tried to access with a CHAIN statement does
not exist in his disk area. The PROGRAM IS message will also occur.

BAD SLEEP ARGUMENT

The argument of the SLEEP statement must have a number greater
than or equal to 0, and less than or
equal to 4095.

ARRAY OR RECORD
USED BEFORE
DEFINITION

The RECORD statement must occur
before any reference to it is made.
A DIM statement must occur before
an array is used. (RECORD and
DIM are placed at the beginning of
a program.)

IMPROPER DIM OR
RECORD STATEMENT

Syntax error in DIM or RECORD
statement, or an array name that was
previously dimensioned is reu:~ed.
(Replaces IMPROPER DIM STATEMENT IN LINE n).

CAN'T CREATE FILE

An OPEN statement tried to create
a file, but there is: (a)· no disk space
available, (b) no file name speciHed,
or (c) a null string has been given
as the file name.

CAN'T DELETE FILE

UNSAVE cannot delete a file. This is
usually due to the fact that another
user has the file open, or the file is
protected with a code ~20.

UNOPEN DISK UNIT

The user tried to do a GET, PUT, or
UNSAVE to device 8 or 9, without
a file being previously opened on the
device.

9-53

Table 9-4 (Cont.).

BASIC Error Messages

Message

Explanation

DEVICE BUSY

The user tried to OPEN DECtapes
0-7, line printef, or paper tape punch,
but the device was unavailable, and
there was no ELSE clause in the
OPEN statement.

INVALID RECORD NO.

The record number must be ,a number which is greater than or equal to
o and less than or equal to 4095. For
DECtape II 0 the maximum record
number is limited further by the
DECtape size.

ON INDEX OUT OF
RANGE

The value of the index is less than
one, or greater than the number of
statement numbers.

INVALID DEVICE NO.

The device number' in the file II 0
statement is not between 0 and I I inclusive, (or X and 11 inclusive where
X is a number set by the system
manager) .

GET BEYOND END OF

Disk data file is too small to have
a record with the number specified in
the GET statement at line n.

FILE

GET/PUT ERROR

A hardware error occupied in GET
or PUT. (This is usually due to a
DECtape unit being write-locked.)

CHAIN TO BAD FILE

The file specified by the CHAIN has
an invalid format: it is not a BASICformat file. The "PROGRAM IS ... "
message will follow this error message. The program name will be the
name of the bad file.

9-54

Table 9-5.
Message
/0

UN
. LN

SQ
PW

Non-Fatal Execution Errors

Explanation
Zero divide-an attempt was made to divide by zero.
The largest possible number is used for the result.
Overflow-the result of a calculation was too large
for the computer to handle. The largest possible
number is used for the result.
Underflow-the result of a calculation was too small
for the computer to handle. Zero is used for the
result.
An attempt was made to compute the logarithm of
zer~ or. a negative number. Zero is used for the
reKllt.
An attempt was made to compute the square root of
a negative number. The square root of the absolute
value is used for the result.
An attempt was made to raise a negative number
to a fractional power. The absolute. value of that
number raised to the fractional power is used.

9-55

Table 9-6.

Statement

EduSystem 50 BASIC Language Summary .

Format

Input/ Output Statements
CLOSE
CLOSE f
DATA
DATA n l ,n 2, ... nn
GET
GET f,l,r
INPUT
INPUT VI '2, ... Vn
LINPUT
LINPUT v$1,V$2, ... V$n

\0
VI

LPRINT

LPRINT el,e2, ... el~

OPEN
OPEN-ELSE
PRINT
PUT
READ
RESTORE
RESTORE *
RESTORE$
UNSAVE

OPEN f,n$
OPEN fELSEn
PRINT e 1 ,e 2,...e n
PUT f,l,r
READ VI,V 2 , ... vn
RESTORE
RESTORE *
RESTORE$
UNSAVEf

0"1

Explanation
Close file f.
Numbers nl through nn = variables in READ statement.
Read record r from file f into the variables in line i.
Get VI through Vn ,input from the Teletype.
Get long character 'string input from Teletype (up to 50
characters) .
Print values of specified text or expressions on line printer
or high-speed paper tape punch.
Open a file named n$ as file number t.Open a file, go to line n if unavailable.
Print values of specified text, variables, or expressions.
Write record r, formatted as in line 1, into file f.
Read variables v through v from DATA list.
Reset DATA pointer to beginning value.
Reset DATA pointer for numeric data only.
Reset DATA pointer for character string data only.
Delete file f from disk storage.

Table 9-6 (Cont.).

1.0
I

VI
-.l

EduSystem 50 BASIC Language Summary

Statement

Format

Explanation

Transfer of Controls
GOTO
IF-GOTO

GOTO 1
IF e 1 r e:! GOTO 1

Transfer control to line number 1.
If relationship r between el and e 2 is true, transfer control to line number 1.
Same as IF-GOTO.
Computed GOTO.

IF-THEN
ON-GOTO
Loops and Subscripts
DIM
FOR-TO-STEP

IF e l r e:! THEN 1
ON e GOTO II,l:!, ... l;;

NEXT v

Subroutines
GOSUB
RETURN

GOSUB 1
RETURN

STOP
Others
CHAIN
CHANGE

DIM v(d 1), v(d1,d;l)
FOR v=e 1 TO e:! STEP e;;

Enter subroutine at line 1.
Return from subroutine to statement following GOSUB
statement.
Transfer control to END statement.

STOP
CHAIN n$
CHANGE VI TO

Dimensions, variables subscripted.
Set up program loop. Define v values beginning at e l to
e 2 • incremented by e 3 •
Terminate program loop. (Increment value of v until
v>e2·)

Link to next program.
Change character string to array of character codes or
vice versa.

Table 9-6 (Cont.).

Statement

'P.

DEF
END
LET
RANDOMIZE
REMARK
SLEEP
Edit/ Control Commands
BYE
CATALOG
COMPILE
CTRL/C
DELETE

Format
DEF FNA(x)=f(x)
END
LET v=f
RANDOMIZE
REM. text
SLEEP n
BYE
CAT
COM name
CTRL/C
DELn
n

EDIT

DEL n,m
EDln

EduSystem 50 BASIC Language Summary

Explanation
Define a function.
End of program.
Assign value of formula f to variable v..
Randomize random number routine.
Insert a remark or comment.
Cause program to pause for n seconds.
Leave BASIC Monitor.
List names of programs in storage area.
Compile program in core and save it on disk.
Stop program execution; return to edit phase.
Delete line n.
Delete line n.
Delete lint;:s n through m, inclusive.
Search line n for character c.

(c)

KEY
LIST

KEY
LIST
LISTn
LISTn,m

Return to keyboard mode after TAPE.
List entire program in core.
List line n only.
List lines n through m, inclusive.

Table 9-6 (Cont.).

\0
I
VI
\0

EduSystem 50 BASIC Language Summary

Statement

Format

Explanation

LLIST
NEW
OLD
REPLACE
RUN
SAVE
SCRATCH
TAPE
UNSAVE

LLIST
NEW
OLD
REP
REP name
RUN
SAVE name
SCR
TAP
UN SAVE name

List program to line printer.
Clear core, request program name.
Clear core, bring program to core from storage area.
Replace old file on disk with version in core. If name
is not specified, old name is retained.
Compile and run program in core.
Store program named on storage device.
Erase current program 'from core.
Read paper tape; suppress printing on Teletype.
Delete program named from storage device.

Functions
ABS
ATN
COS
EXP
INT
LOG
RND
SGN
SIN

ABS(x)
ATN(x)
COS(x)
EXP(x)
INT(x)
LOG(x)
RND(x)
SGN(x)
SIN (x)

Absolute value of x.
Arctangent of x (result in radians).
Cosine of x (x in radians)
e (e=2.712818).
Greatest integer of x.
Natural logarithm of x.
Random number.
Sign of x (+ 1 if positive, -1 if negative, 0 if zero).
Sine of x (x in radians).

Table 9-"6 (Cont.).
~t~tement

\0
I
0\

SQR
TAN
TAB
FIX
CHR$

EduSystem 50 BASIC Language Summary

Format

Explanation

SQR(x)
TAN(x)
TAB(x)
FIX(x)
CHR$(x)

Square root of x.
.
Tangent of x (x in radians).
Controls printing head position on Teletype.
Truncates decimal portion of x.
Converts character code to character. Used only with the
PRINT statement.

FOCAL
FOCAL (FOrmula CALculator) is an on-line~' interactive,
service program for the PDP-8 family of computers, designed to
help scientists, engineers, and students solve numerical problems.
The language consists of short imperative English statements
which are easy to learn. FOCAL is used for simulating mathematical models, for curve plotting, for handling sets of simultaneous
equations, and for many other kinds of problems.
To call FOCAL, type:
.R FOCAL

FOCAL enters its initjal dialogue, and asks if its extended functions are to be retained. The extended functions are exponential,
sine, cosine, arctangent, and logarithm. If the FOCAL program
to be run uses any of these functions, the user responds YES.
If not, the user responds NO to free more space for the user program. Without the extended functions, there is room for approximately 1800 characters of program. If the extended functions are
retained, there is room for approximately 1100 characters.
Using FOCAL Commands
Whenever FOCAL prints any asterisk, it is in command mode,
and the user may type any of the FOCAL commands in response
to the asterisk. FOCAL commands may be direct or indirect. A
direct command is typed directly after the asterisk and is .executed
immediately. The format for direct commands is:
*COMMAND
An indirect command is always identified by a line number.
Indirect commands are not executed until program control passes
to the line number associated with the command. The format for
indirect commands is:
*GG.ss COMMAND
When the user is typing indirect commands, he may use any
line number in the range 1.01 to 31.99, except those ending in
.00. Numbers such as 1.00 or 31.00 are illegal as line numbers;
9-61

,they are used to identify an entire group of line numbers. Line
numbers. are typed in the format:
GG.ss
where GG is the group number and ss is the step number. It is
not necessary to type two digits after the" decimal; e.g., 2.1 is
equivalent to 2.10.
All FOCAL commands must be followed immediately with a
space. All FOCAL command lines must be terminated with the
RETURN key.
FOCAL Overview

FOCAL consists of 12 commands which are all the beginner
needs to write programs. FOCAL commands may be typed in their
entirety or abbreviated. The FOCAL commands are:
Command

Explanation

TYPE

Used to print text, results of calculations, and values of variables.

ASK

Used to assign values to variables
from the keyboard.

SET

Used to define variables and evaluate expressions.

GO or GOTO

Used to direct program control to
the lowest line number, or to some
specific line number.

Used to direct program control
conditionally after a comparison.

Used to cause a specific line or
group of lines "to be executed.

RETURN

Used to terminate DO routines.

QUIT

Used to halt program execution
and return control to user.

FOR

Used to increment number and
execute a user-specified command
for each value of the number incremented.

9-62

Command

Explanation

COMMENT or
CONTINUE

Used for comments or non-executable program steps.

ERASE or
ERASE ALL

Used to erase part of a program
or an entire program.

MODIFY

Used to edit words or characters
on a program line.

These commands are explained in detail with actual computer
output in this section. For the convenience of the user, a detailed
FOCAL command summary is included in Table 9-7.
Numbers.
A FOCAL number may be any decimal number between -1 onl"
and 10615 • Numbers may be written signed (+ or -) or unsigned,
either with a decimal point and a fractional part or in exponential
format (see Data Formats) with a mantissa and exponent. In
FOCAL, all numbers are internally represented in exponential
format, retaining up to six significant digits. If more than six
digits are specified, the number will be rounded to six digits. The
following numbers are identical in FOCAL:
60
60.00
6E10
600E-I0
60.00003
Variable Names
FOCAL variable names may consist of ei ther one or two char-·
acters. The first character must always be alphabetic; however, it
cannot be an F becaluse FOCAL reserves that character for func-·
tion names (see FOCAL Functions). The second character may
be either alphabetic or numeric. The user may write variable names
consisting of more than two characters, but FOCAL uses only the
first two characters to identify the variable. a Therefore, the first
two characters must be unique.
3 A variable is represented internally as a binary fraction with an exponent. See Data Formats.

9-63

*SET
*SET
*SET
*SET
*SET
*SET

A=56789
B=123456
Cl=15
C2=30
DEPTH=10
DISTANCE=Cl+C2

Variables may also be sUbscripted. For a discussion of what
subscripted variables are and how they are used, see Subscripted
Variables.
Arithmetic Operations

To print the· results of arithmetic calculations, the user types
the FOCAL command TYPE followed by a space and the data
to be calculated. Then he presses the RETURN key, and FOCAL
prints the answer. For example:
*TYPE 6+10-3-1
12.0000*

The above example shows two of the arithmetic operati9lls
(+ and -) performed by FOCAL. Arithmetic operations are performed from left to right except when the operation to the right
has priority or when enclosures are used. (See Enclosures.)
*TYPE 6+5; TYPE 5+2-3; TYPE 10-6

= .

11. 0eJ00=

4.0000=

4.0000*

NOTE
Several commands may be typed on· the
same line if they are separated by semicolons (;). This is true for all FOCAL commands .except the LIBRAR Y commands.
Unless indicated otherwise, FOCAL mathematical computations
retain an accuracy of six. significant digits.
PRIORITY OF ARITHMETIC OPERATIONS
The .FOCAL arithmetic operations priorities are:
First priority -exponentiation (t) 4
Second priority -multiplication (*)
4 When exponentiation is performed by FOCAL, the power to which a
number is raised must be a positive integer. If a calculated exponent exceeds the limits of size, no error message is given. The result will go to
zero.

9-64

Third priority --division (I)
addition (+)
Last priority
subtraction (-)

When FOCAL evaluates an expression which includes several
arithmetic operations, the above order of priority is followed.
Therefore, FOCAL evaluates .

to have a value of

because multiplication (*) has a higher priority than addition (+).
ENCLOSURES
The order of executing arithmetic operations is also influenced by
enclosures. Three kinds of enclosures may be used with FOCAL:
parentheses (), square brackets []~, and angle brackets <>.
FOCAL treats them all the same. For example, the result of the
expressIon:

is the same as the result of:
*TYPE **

If the expression contains enclosures within enclosures (called

nesting), FOCAL executes the contents of the innermost enclo··
sures first and works outward.
*TYPE <5*<2+3>-5>t2
400.0000*

[and] are typed by SHIFT/K and SHIFTn"1;, respectively.

9-65

Input/ Output Commands

TYPE COMMAND
The TYPE command is used to print results of calculations,
values of variables, text or character strings, and variable tables.
TYPE may also be used to print combinations of text and variables.
Example I-Result of a Calculation:
*TYPE 1+1

2.eleleleI*

Example 2-Value of a Variable or Variables:
*SET N=5+5: SET M=3e1
*TYPE N~M
10.0000=

Example 3-Text:
*TYPE "THIS IS A LINE OF
THIS IS A LINE OF TEXT

TEXT"~

*
Example 4-Variable Tables:
*TYPE

N(H eleI) =

Mi(eleI)=

*
The user may command FOCAL to print all of the user-defined
variables (variable table) by using the TYPE command and a
dollar sign ($).
If a variable consists of only one letter, an at sign (@) is inserted as a second character in the variable table printout, as shown
in the example above.
*SET N=25
*TYPE "N IS"~N
N 15=
25. eIeI 115 115*

NOTE
Any variable, constant, or expression in a
TYPE or ASK command must be followed
by a comma, semicolon, or carriage return.
(l

The exclamation mark (!) causes a carriage return and line feed.

9-66

ASK COMMAND
The ASK command is normally used in indirect commands to
enable the user to input numerical data during the execution of his
program. The ASK command is similar to the TYPE command in
form, but only single variable names, not expressions, are use:d;
and the user-types the values in response to a colon (:) printed by
the ASK command.

When FOCAL encounters line 11.99 in the above example, it
prints a colon and waits for the user to type a value (in any
format) and a terminator7 for the first variable. This process continues until all the variables in the ASK command have been given
values.
The value is assigned to the variable when the user types a terminator; so any time before the terminator is typed, the value can be
changed. If the user types back arrow (~ or SHIFT /0) immediately after the value and before he types a terminator, he can then
type the correct value and a terminator.

:6
:8"7
*TYPE X" ! " Y" !" Z

=
=
=

5.13131313
6.13131313
7.13131313*

User typed 5 and RETURN key.
User typed 6 and RETURN key.
User typed 8, ~, 7 and RETURN
key.

The ALT MODE key is a special non-spacing terminator which
enables the user to have a previously assigned value unchanged.

:3
: : 12
*TYPE

=
=
=

x ..

I" Y.. !" Z

3.13131313
6.13131313
12.13131313*

User typed ALT MODE because
he did not want to change the
value of Y.

7 Terminators are SPACE, comma, ALT MODE, and RETURN keys. If
the user types the RUBOUT key, it is ignored.

9-67

Text Output with ASK
The ASK command, just as the TYPE command, may be used
to print text. Carriage return and line spacing are controlled the
same as with the TYPE command (see Data Formats).
*ASK "WHAT IS YOUR AGE?"- AGE
WHAT IS YOUR AGE?:19

*
The word following the text in the command line (AGE, in this
example) is the variable.
Computational Command
SET COMMAND
The SET command enables the user to assign a numerical value
to a variable and store both the value and the variable. Then, when
he uses the variable in an expression, 8 FOCAL automatically substitutes ·the numerical value that the user previously specified:
*SET E=2.71828
*SET PI=3.14159
*TYPE "PI TIMES E"I PI*E
PI TIMES E=
8.5397*

The value of a variable may be changed at any time by another
SET command.
*SET Al= 3' 2
*SET Al=Al+l
*TYPE Al
10.0000*
=

Control Commands
GO OR GOTO COMMAND
. The GO command causes FOCAL to go to the lowest numbered
line in the program and begin executing the indirect commands.
* 1. 1
* 1.3
* 1.5
*GO
=

SET A= 1
SET B=2
TYPE AlB
1.0000=

2.0000:

8 An expression is a combination of arithmetic operations or functions
which may be reduced to a single number by FOCAL.

9-68

In the above example the GO command caused execution to begin
at line 1.1.
The GOTO command causes FOCAL to go to a specific line in
the program and begin executing the indirect commands in ascending line number order.
*ERASE
* 1. 1 SET A= 1
*1.3 SET B=2
*1.5 TYPE A.. B
*GOTO <1.3
=

0.0000=

2'. (iH?J00:

:ERASE

In the preceding example, A and B are equal to zero at the start
of the program. The ERASE and ERASE ALL commands are used
to ensure that all variables are equal to zero until they are assigned
a specific value. Since the GOTO command causes program exec:ution to begin at line 1.3, line 1.1 is never executed and A is not set
to 1.
IF COMMAND
The IF command is a conditional command used to transfer program control after a comparison. The normal IF command format
IS:

IF space (expression) line1, line2, line3
The expression or variable is evaluated, and program control is
transferred to the first line number if the value of the expression
is less than zero, to the second line number if the value is zero, or
to the third line number if the value is greater than zero.
The program below transfers control to line number 2.1, 2.3, or
2.5, according to the value of the expression in the IF command.
*2.1 TYPE "LESS THAN ZERO"; QUIT
*2.3 TYPE "EQUAL TO ZERO"; QUIT
*2.5 TYPE "GREATER THAN ZERO"': QUIT
*IF <25-25>2.1 .. 2.3 .. 2.5
EQUAL TO ZERO*

IF with Less Than Three Line Numbers
The IF command format can be altered to transfer program control to one or two lines. For example, if a semicolon or a carriage

9-69

return is immediately after the first line number, control. goes to
the first line number if the value of the expression is less than zero.
If the value is not less than zero, control goes to the next sequential
command. For example:
*2.20 IF (X)I.8;TYPE"Q"

When line 2.20 is executed, program control goes to line 1.8 if X
is less than zero. If Xis not less than zero, Q is typed.
If a semicolon or a carriage return follows the second line number, control goes to the first or second line number, depending upon
whether the value of the expression is less than zero or equal to
zero. If the value is greater than zero, control goes to the next
sequential command. For example:
*3.19 IF (B)I .. I.9
*3.20 TYPE B

If B is less than zero, control goes to line 1. 8; if B equals zero,

control goes to 1.9; and if it is greater than zero, control goes to the
next sequential command, in this case line 3.20, and the value of B
is printed.
Arithmetic Comparison with IF Command
The IF command can be used with all the arithmetic operations
of FOCAL. Example I-Addition:

Example 2-Subtraction:

* 5. 1 6

I F ( A- 8.) 1 • 6;

T Y P E "X"

Example 3-Division:
*3.10 IF (M/N)5.5 .. 5.6;
*3.15 TYPE "GREATER THAN ZERO"

Example 4-Multiplication:

7. 20 I F (P* I ) 8. 1;
*7.25 TYPE P*I

9-70

Example 5-Exponentiation:

DO COMMAND
The DO command is used to make subroutines of single lines or
groups of lines. Control is returned to the line following the DO
command after the subroutine is executed.
*1.1 SET A=I; SET B=2
*1.2 TYPE "STARTING"
*1.3 DO 3.2
*2.1 TYPl:; "FINISHED"
*3.1 SET A=3; SET B=4
*3.2 TYPE A+B
*GO
STARTING=
3.0000FINISHED=

*
If the user types a command such as DO 3, the DO command
treats the group of program lines beginning with 3 as a subroutine.
Control proceeds in ascending order through the group numbers
until the end of the group is reached, or until a RETURN command is executed.

Nested DO
DO commands may be nested as shown in the following example:
* 1 • 1 TYPE "BEGIN" .. !
* 1. 2 DO 2
*1.3 TYPE "END" .. !; QUIT
*
*2.1 DO 5. 1; TYPE A.. !
*2.2 DO 5.2; TYPE A.. !
*2.3 DO 7.5; TYPE A.. !
*
*5. 1 SET A=1
*5.2 SET A=2
*
*7.5 SET A=3
*GO
BEGIN
=
1.0000
=
2.0000
=
3.0000
END

*
9-71

The number of nested DO commands is limited only by the
amount of core memory available after storage is allocated for
program and variables.
RETURN COMMAND
The RETURN command is used to exit from a DO subroutine.
When a RETURN command is encountered during execution of a
DO subroutine, the program exists from its subroutine status and
returns to the command following the DO command that initiated
the subroutine status.
QUIT COMMAND
When the QUIT command is executed, FOCAL prints an
asterisk and retuf11s to j;ommand mode.
FOR COMMAND
The FOR command is used to set up program loops and iterative
procedures. The general command format is:
*FOR A
*FOR A

= B,C,D; commands
= B,D; commands

The variable A is initialized to the value B, then the command
or commands following the semicolon are executed: When the commands have been executed, the value of A is incremented by C and
compared to the value of D. If A is less than or equal to D, the
command after the semicolon is executed again. This process is
repeated until A is greater than D, at which time FOCAL goes to
the next sequential line. The command or commands will always be
executed at least once.
A must be a single variable. B, C, and D may be expressions,
variables, or numbers. If the value C is omitted,it is assumed that
the increment is one. If C and D are omitted, the FOR command is
handled like a SET command and no iteration is performed. A
FOR command may be used with a DO command and nested:

9-72

FOR with aDO
*ERASE ALL

* I. 1
* 1.2

FOR X=I .. I .. 51 DO 2

QUIT

**2. 1

TYPE fit
*2.2 SET A=X+100
*2.3 TYPE !It
*GO
X=
A=
X=
A=
X=
A=
X=
A=
X=
A=

X" .. X
AIt .. A

1.0000
101.0000
2.0000
102.0000
3.0000
103.0000
4.0000
104.0000
5.0000
105.0000*

Nested FOR and DO
* 1. 1
* 1. 2
*1.5
*1.7
*
*3. 1

FOR Z=I .. 3; TYPE

TYPE !
FOR A= I .. 3J DO 3

QUIT
FOR B= I .. 3J

DO 4

>I<

*4.1 FOR c= I .. 31
*4.2 TYPE
*GO
A
A B C
= 1= 1= 1 = 1=
= 1= 2= 1 = 1=
= 1= 3= 1 = 1=
= 2= 1= 1 = 2=
= 2= 2= 1 = 2=
= 2= 3= 1 = 2=
= 3= 1= 1 = 3=
= 3=·2=
= 3=
= 3=
= 3= 3=
*

TYPE % I .. A.. B .. C..
B
1=
2'"
3=
1=
2=
3=
1=
2=
~J=

C
2
2
2
2
2
2
2
2
2

=
=
=
=
=
=
=
=
=

A
1=
1=
1=
2=
2=
2=
3=
3=
3=

1=
2=
3=
1=
2=
3=
1=
2=
3=

C
3
3
3
3
3
3
3
3
3

Another way of handling the same program is:
*1.1 FOR Z=1 .. 3.:TYPE"
A
8
C ..
*1.2 FOR A=1 .. 3;FOR 13= 1.. 3.: TYPE !;FOR C=1 .. 3JTYPE

*0'0

9-73

%~ ..

A .. 8 .. C.. "

Subscripted Variables
Variables may be further identified by subscripts which are enclosed in parentheses immediately following the variables. For
example:
*SET AB(0)=S
*SET AB(I)=10
*SET AB(2)=IS
*SET AB(3)=20
*SET AB(4)=2S
*SET AB(S)=30
*FOR X=0 I S; TYPE AB(X)I!
=S
= 0.1E+02
= 0.2E+02
= 0.2E+02
= 0.3E+02
= 0.3E+02

In the above example, sUbscripts are used to set up an array
cal1ed AR. Any element in the array can be represented by a subscript in the range 0 to 5. The first element in an array always has a
subscript of O. A sUbscript may be a number, another variable., or
an expression. If it is a number, it must be in the range ±2047. In
order to be properly represented by the TYPE $ command, subscript numbers must be positive integers in the range from 0 to 99.
The TYPE $ command will· print subscripts greater than 99 as two
random characters, although their contents will be correct as assigned by the program.
COMMENT OR CONTINUE COMMAND
The COMMENT or CONTINUE command (abbreviated as C)
causes the program line to be ignored by FOCAL. The user may
use the C command to insert comments into the program, or he
may use the C command line as a. non-executable program step.
In either case, program lines beginning with C are skipped wh~n
the program is executed. However, comments are printed in response to a WRITE q)mmand.
9-74

*ERASE ALL
*1.1 C INITIALIZE VARIABLES
* 1.2 SET A= 5
*1.3 SET B=6
* 1. 4 SET C= 7

**2.1

C PERFORM CAL.CULATION
*2.2 TYPE A+B+C

*
Edit Commands

WRITE OR WRITE ALL COMMAND
The WRITE or WRITE ALL command causes FOCAL to
print a program line, a group of lines, or an entire indirect program
on the Teletype.
*WRITE 2.1
*WRITE 2
*WRITE

Print a single line.
Print a group of lines.
Print an entire program.

Once the program is completed, the user may want to save it by
putting it on paper tape. The procedure for saving a FOCAL program on-line is as follows:
1.
2.
3.
4.

Make sure FOCAL is in command mode.
Type WRITE
Set low-speed punch to ON position.
Type RETURN key.

FOCAL will punch the entire program onto the paper tape and
simultaneously print it on the Teletype.
Whenever the user wants to run, the program he has saved on .
paper tape, he does the following:
1. Makes sure FOCAL is in command mode.
2. Puts the program tape in low-speed reader.
3. Switches the low-speed reader to START.
The program will be put into core the same as it would if the
user were typ~ng it on the Teletype keyboard. When the entire
program has been read into core, the user should type CTRL/C
since the asterisk printed when the WRITE command is finished
is also punched and may be interpreted as a command. CTRL/C
ensures that FOCAL returns to command mode.
9-75

ERASE AND ERASE ALL COMMANDS
The ERASE command de1etes symbolic names, lines, or groups
of lines.
.

*ERASE 2.2
*ERASE 2

Delete all names defined in
symbol table.
Delete line 2.2
Delete all lines in group 2.

The user can check to see if the line(s) has been deleted by
typing the WRITE command after the ERASE command. This is a
useful procedure for checking commands and also for obtaining a
clean printout of the current program.
The ERASE ALL command deletes the entire indirect program.
It is good programming practice to type ERASE ALL before starting to type a new program. The ERASE ALL command is generally used only with direct commands because it returns control
to command mode upon completion.
MODIFY COMMAND
The MODIFY command is used to change characters within a
line without changing the entire line. The format for MODIFY is:
MODIFY line number RETURN key Search character
The search character is not printed. After the user has typed the
line number, RETURN key, and search character, FOCAL prints
the contents of the specified line until it encounters the search character. When the search character is read and printing stops, the
user has anyone or more of the following options:
1.. Type new characters in addition to those already printed.
2. Type a form feed (CTRL/L). This causes the· search to
proceed to the next occurrence, if any, of the search character.
3. Type CTRL/BELL; The user can then change the search
character he specified in the MODIFY com1J1and.
4. Type the RUB OUT key. This causes FOCAL to delete a
character, starting with the last character printed and deleting one character to the left each time RUBOUT is
typed.
9-76

5. Type the back arrow (~) key. This causes FOCAL to
delete everything between the back arrow and the line number.
6. Type the RETURN key. This causes FOCAL to terminate
the line at that point, deleting everything to the right.
7. Type the LINE FEED key. This is normalJy done after the
user has exercised one or more of the above options. After
the user has modified the line, he may type LINE FEED
and cause the remainder of the line from the search character to the end to be printed and saved.
*7.01 JACK AND BILL W$NT UP THE HILL
*MODIFY 7.01
JACK AND B\JILL W$\ENT UP THE HILL

In the above example, B was typed as the search character for
line 7.01. (Note that the search character did not print.) FOCAL
stopped printing when it encountered the search character (B), and
the user typed the RUBOUT key ("') to delete the B. Then he
typed the correct letter J. Next he typed CTRLjBELL and the $
key to change the search character. FOCAL continued to print the
line until the new search character was encountered. The user typed
R UBO UT to delete the $ and then typed the correct character (E).
He then typed the LINE FEED key and the remainder of the line
was printed.

CAUTION
When any text editing is done. the values in
the user's symbol table are reset to zero.
If the user defines his symbols in direct statements and then uses
a MODIFY command, the values of his symbols are erased and
must be redefined. However, if the user defines his symbols by
means of indirect statements prior to using a MODIFY command,
the values will not be erased because these symbols are not entered
in the symbol table until the statements 4efining them are executed.
Notice in the example below that the values of A and B were set
using direct statements. The use of the MODIFY command reset
their values to zero and listed them after the defined symbols.

9-77

*ERASE ALL
*SET A=1
*SET B=2
* 1.1 SET C=3
*1.2 SET D=4
*1.3 TYPE A+B+C+D; TYPE !1 TYPE $
*MODIFY 1.1
SET C= 3\5
*GO
107.22 @ 01.10

**MODI FY

1. 1
SET C= 3\5
*GO
::: 9
C@(00)= 5
D8(00)= 4
Aie (0)= 0
B@(00)= 0

*
Library Commands
In addition to the basic FOCAL commands, there are four
special commands to perform the library functions: storing and
retrieving data from the system disk. All commands following the
LIBRARY command on the same line are ignored. Names of files
may be from 1 to 4 characters long. Only alphanumeric characters,
letters, and numbers should be used in file names. The library commands, like other FOCAL commands, may be abbreviated.
LIBRARY SAVE
This command copies the current program into the user's area
on disk and gives it the name specified. For e,xample, the command:
*L S TRUE

will cause the current program to be stored on disk under the name
TRUE. The program will also remain in the user's area.
LIBRARY CALL
This command copies the named program from disk into the user's
area. For example, the commands:
*L C TRUE

*w
will cause the program TRUE to be recalled from the disk.into the
user's area and listed on the Teletype. Any program currently in
9-78

the user's area will be erased. The program TRUE can then be
executed with a GO command.
If the LIBRARY CALL command is given a line number and
stored, it must have at least one numbered command following it.
In this case, the LIBRARY CALL command will cause the named
program to be called into the user's area and executed as if GO
had been typed. For example:
*3.10 L C TRUE
*3.11 C

If the above commands are included in a program, they w~ll
cause TRUE to be brought in and executed at that point. If there
are lines beyond 3.11 remaining to be executed, they will be deleted.
This procedure allows the user to chain FOCAL programs as in
BASIC.

LIBRARY DELETE
This command deletes the named program from the disk directory. For example, the command:

*L D TRUE

will remove TRUE from the disk.
LIBRARY LIST
This command causes the names of all the FOCAL programs
stored on the disk to be listed on the Teletype, ten names to a line,
followed by the total number of free blocks remaining on the disk.
The LIBRARY LIST command removes the contents of the user's
area with an ERASE ALL command.
ERROR MESSAGES WITH LIBRARY COMMANDS
When the . LIBRARY commands are used, five errors are possible. These are also listed iIi the error code summary in Table 9-9
at the end of this section.
9-79

Command
?30.71

Explanation
The command appeared to be a LIBRARy command but was not, for example:
LIBRARY OPEN
No action is taken; the command should
be retyped.

?30.<0

Either an unacceptable file name was
specified or no name was specified where
one was required.

?31.42

The file name specified does not match
any name currently in the user's disk
directory. This error will only occur with
the LIBRARY CALL and LIBRARY
DELETE commands.

?31.43

There is already a program with the specified name in the directory. This error
will only occur with the LIBRARY
SAVE command.·

?31.44

This user's disk directory is full. The current program cannot be saved until others
have been deleted. This error will only
occur with the LIBRARY SAVE command.

Estimating Program Length
FOCAL permits approximately 1060 (decimal) locations to be
used for the user program and variables without the extended math
functions, and approximately 670 locations with the ext~nded functions (sine, cosine, log, exponential, etc.). Since FOCAL requires
five locations for each variable stored in the variable table and one
location for each two characters of stored program, the approximate length of a program may be determined by the formula:

9-80

Length of program

= 5S + 2 + 2L

where
S = number of variables
C= number of characters in program
L = number of lines
If the total program area or variable table area becomes too
large, FOCAL prints an error message (06.54 or 1-0.: 5). The following routine allows the user to find out how many core locations
are left for his use:

*ERASE
? 06. 54
*TYPE %4"I*5,,"LOCATIONS LEFT"
= 1075LOCATIONS LEFT*

(Disregard error code.)

*
*
Debugging
USING THE ERROR DIAGNOSTICS
Whenever FOCAL detects an illegal command or improbable
condition within a user's program, the execution of the program
stops and an error message is printed in the form ?XX.XX@GG.ss,
where ?XX.XX is the error message and GG.ss is the line at which
the error occurred. (See Table 9-9 for the complete list of error
messages.)
Depending upon the type of error detected, the user may ignore
the error message or make program changes before continuing. For
example, if the user types CTRL/C to terminate a loop, the error
message ?01.00 is printed and program control goes to command
mode; so, in this case, the user ignores the message and, types his
next command. !fa program stops and the message ?03.05 is
printed, the user must examine his program to determine which
command line is wrong. In the following program, line 1.3 contains
the instruction to transfer to a nonexistent line number.

9-81

*ERASE ALL
*1.10 SET A=2; TYP~ "A"IAI!
*1.20 SET B=4; TYPE; "B"IBI!
*1.30 GOTO 1.01
*1.40 TYPE "A+B"IA+B
*GO
A=
2
B=
4
?03.05 @ 01.30

*
USING THE TRACE FEATURE
The trace feature is used to check the logic in part of a FOCAL
program. To imp.lement the trace feature, the user inserts a question mark (?) into a command string at any point. FOCAL prints
each succeeding character as it is executed until another question
mark is encountered or until the program returns to command
mode. For example, the trace feature is used to print parts of 3
lines in the following program:
*ERASE ALL
* 1 • 1 SET A= 1
*1.2 SET 8=5
*1.3 SET C=3
*1.4 TYPE ?A+B-C?I!
*1.5 TYPE ?B+A/C?I!
*1.6 TYPE ?B=C/A?
A+B-C=
B+A/C=

3
5

8=C/A=

NOTE
The WRITE command disables the trace
feature.
FOCAL Functions
The FOCAL functions improve and simplify arithmetic capabilities. In general, the FOCAL functions may be used anywhere a
number or a variable is legal in a mathematical expression. A
standard function call consists of three or four letters beginning
with the letter F and followed by an expression in parentheses. The
FOCAL functions are summarized in Table 9-8.
9-82

The functions must be used with a legal FOCAL command. They
cannot be used alone as commands. For example:
*SET Z=A+FSQT(FSIN(X»

Within a normal range of arguments, at least five significant
digits of accuracy may be expected for the trigonometric, exponential, and logarithmic functions. The following functions are available to FOCAL users.
SINE FUNCTION (FSIN)
The sine function (FSIN) is used to calculate the sine of a
user-specified angle in radians. The format for FSIN is:
FSIN (angle)
*TYPE FSIN(3.14159/4)
=
0.7071*

The format for calculation the sine of an angle in degrees is:
FSIN (degrees
*TYPE

* 3.14159/180)

FSIN(30*3.14159/1R~)
0.5~~~~*

COSINE FUNCTION (FCOS)
The cosine function is used to calculate the cosine of a userspecified angle in radians. The format for FCOS is:
FCOS (angle)
*TYPE FCOS(2*3.141592>
=
1 .0el00*
*TYPE FCOS(.50000>
=
0.8776*
*TYPE FCOS<45*3. 141592/180>
=
0.7071*

9-83

EXPONENTIAL FUNCTION (FEXP)
The exponential function. (FEXP) is us.ed to compute e
(e=2.71828) to a power specified by the user. The format for
FEXP is:
FEXP (power)
*TYPE FEXP C1 )
2.7183*
*TYPE FEXP(0)
=
1.0000*
*TYPE FEXPC-1-23456>
=
0.0000*

LOGARITHM FUNCTION (FLOG)
The logarithm function (FLOG) is used to compute the natural
logarithm (loge) of a number specified by the user. The format for
FLOG is:
FLOG (number)
~TYPE

FLOGCl.(0000)

= 0.0000*
*TYPE FLOG(I.98765)
=
0.6870*
*TYPE FLOGC2.(65)
=
0.7251*

The following formulas are useful for finding logarithms to base
10:
logloX=10geX/1oge 10=0.434294 10geX
ARCTANGENT FUNCTION (FATN)
The arctangent function (FATIN) is used to calculate the angle
in radians of a user-specified tangent. The format for FATN is:
F ATN (tangent)
*TYPE FATN C1 • )
0.7854*
*TYPE FATN(.31305)
=
0.3034*
*TYPE FATN(3. 141592)
=
1.2626*·

9-84

SQUARE ROOT FUNCTION (FSQT)
The square root function (FSQT) is used to compute the square
root of an expression. The format for FSOT is:
FSQT (expression)
*TYPE FSQT(4)
=
2.00(i"~*
*TYPE FSQT(9)
=
3.0000*
*SET Z=FSQT(144);TYPE Z
=
12.0000*

ABSOLUTE VALUE FUNCTION (FABS)
The absolute value function (FABS) is used to indicate the
absolute (positive) value of an expression. The format for FABS
IS:

FADS (expression)
*TYPE FABS(-66)
= 66.0000*
*TYPE FABS(+23)
= 23.0000*
*TYPE FABS(-99.05)
= 99.0500*

SIGN PART FUNCTION (FSGN)
The sign part function (FSGN) is used to output the. sign part
(+ or -) of a number with a value of 1. FSGN (0) = 1. The
format for FSGN is:
FSGN (expression)
*TYPE FSGN(6-4)
=
1.0000*
*TYPE FSGN (0)
=
1.0000*
*TYPE FSGN (-7) .
=1.0000*

9-85

INTEGER PART FUNCTION (FITR)
The integer part function (FITR) is used to output the integer
part of a number. The format for FITR is:
FITR (expression)
For positive numbers, FITR(X) is the greatest integer function.
For negative numbers, FITRC-X) is the integer part of ,-X. The
greatest integer function for negative numbers is obtained by
FITR(-X)-l. For example:
*TYPE FITR(5.2)
5.0000*
*TYPE FITR(55.66)
= 55.0000*
*TPE
*TYPE FITR(-4.1)
=4.0000* .

RANDOM NUMBER FUNCTION (FRAN2
The random number function (FRAN) is used to generate honstatistical pseudo-random numbers in the range 0.5000 tQ 0.9999.
No argument is used with the FRAN function. The format for
FRAN is:
FRAN (

)

*TYPE FRAN ()
=
0.7376*
*TYPE FRAN ( )
=
0.8959*

FRAN can be used to produce a less biased number. For example:
*SET A=FRAN()
*SET H=A=VITR(A)

The value assigned to B is a random number in the range 0.0000
to 0.9999.
Focal Output Operations
The following is a description of symbols used in FOCAL output
operations:
, 9-86

To set output format,

Symbol

I?xplanation

TYPE %x.y

Where x is the total
number of digits,
and y is the number
of digits to the right
of • the decimal
point.

TYPE %6.3, 123.456 FOCAL prints:
=+123.456

To type symbol table,

TYPE %

Resets output format to floating
point.

TYPE $

Other statements
may not follow on
this line.

Control Characters

FOCAL control characters and their explanations are shown
below:
%

Output format delimiter
Carriage return and line feed
#
Carriage return
$
Type symbol table contents
( )
Parentheses
[] ,
Square brackets
(mathematics)
<>
Angle brackets
""
Quotation marks (text string)
??
Question marks
(trace feature)
*
Asterisk
(high-speed reader input)
SPACE key (names)
RETURN key (lines)
(nonprinting)
ALT MODE key (with ASK statement)
Comma (expressions)
Semicolon (c:ommands and statements)

9-87

Reading FOCAL P3per Tapes

To ensure ~hat FOCAL paper tapes are read without error, they
should be read silently. To do this, type tB (CTRL/B) followed
by UNDUPLEX just prior to reading the tape. This Monitor command suppresses the printing of the program as it is read. As each
line is read, a line feed and FOCAL's asterisk are printed,. indicating that the line is properly stored. After the tape has been completely read, type tB DUPLEX to restore FOCAL to its normal
mode. An example is shown below:
*ERASE ALL
*tBUNDUPLEX

**tBDlIPLEX

*WRITE ALL
C-FOCALI1969
IIIl.(il5
01.06
(ill.10
(ill.2(il
01.30
01.30
01.40

C PROGRAM TO CALCULATE THE HYPOTENUSE OF A
C RIGHT TRIANGLE GIVEN THE TWO SIDES
ASK "SIDES OF TRIANGLE ARE" AlB
SET C=FSQT(At2+Bt2)
TYPE "HYPUTNEUSE
TYPE "HYPOTENUSE IS" CI!
GUTO 1.1

9-88

Table 9-7.
Command

Abbreviation

FOCAL Command Summary
Example of Form

ASK

ASK X, Y,Z

COMMENT

CONTINUE
DO

C
D

C
D04.1

DO 4.0

DO ALL

ERASE

FOR

ERASE
ERASE 2.0
ERASE 2.1
ERASE ALL
FOR i=x,y,z; (commands)

\0
I
00
\0

Explanation
FOCAL prints a colon· for each variable;
the user types a value to define each variable.
If a line begins with the letter C, the remainder of the line will be ignored.
. Dummy lines.
Execute line 4.1; return to command following DO command.
Execute all group 4 lines; return to command following DO command, or when a
RETURN is encountered.
Execute all program lines, until a RETURN
is encountered.
Erases the symbol table.
Erases all group 2 lines.
Erases line 2.1.
Erases all user input.
Where the command following is executed
at each new value.
x=initial value of i.
y=value added to i until i is greater than z.

Table 9·7 (Cont.).
Command

\0
I
\0

Abbreviation
•

FOCAL Command Summary

Example of Form

GO?

GOTO

GOTO 3.4

IF (X) Ln, Ln, Ln
IF (X)Ln, Ln; (commands)
IF (X) Ln; (commands)

LIBRARY CALL
LIBRARY DELETE
LIBRARY LIST
LIBRARY SAVE

LC
LD
LL
LS

LIBRARY CALL name
LIBRARY DELETE name
LIBRARY LIST
LIBRARY SAVe name

Explanation
Starts indirect program at lowest numbered
line number.
Starts at lowest numbered line number and
traces entire indirect program until another
? is encountered, until an error is' encountered, or until completion of program.
Starts indirect program (transfers control to
line 3.4). Must have argument. '
Where X is a defined identifier, ,a value, or
an expressio,n, followed by three line numbers. If X is less than zero, control is transferred to the first line number. If X is equal
to zero, control is to the 'second line number. If X is greater than zero; control is to
the third line number.
Calls stored program from the disk.
Removes program from the disk.
Prints directory of stored program names.
Saves program on the disk.

Table 9-7 (Cont.).

\0
I
\0

FOCAL Command Summary

Command

Abbreviation

MODIFY
QUIT
RETURN

M
R

MODIFY n
QUIT
RETURN

SET
TYPE

S
T

SET A=5/B*C~
TYPEA+B-C;

Example of Form

TYPE A-B, C/E;
TYPE "TEXT STRING"
WRITE

WRITE
WRITE ALL
WRITE 1.0
WRITE 1.1

Explanation
Enables editing of any character on line n.
Returns control to the user.
Terminates DO subroutines, returning to
the original sequenc~.
Defines identifiers in the symbol table.
Evaluates expression and prints = and result in current output format.
Computes and prints each expression separated by commas.
Prints text. May be followed by ! to generate carriage return-line feed, or # to
generate carriage return.
FOCAL prints the entire indirect program.
FOCAL prints all group 1 lines.
FOCAL prints line 1.1.

Table 9·8.

FOCAL Functions
Interpretation

Function

Format

Square Root

FSQT(x)

Where x is a positive number or
expression greater than zero.

Absolute Value

FABS(x)

FOCAL ignores the sign of x.

Sign Part

FSGN(x)

FOCAL evaluates the SIgn part
only, with 1.0000 as integer.

Integer Part

FITR(x)

FOCAL operates on the integer
part of x, ignoring any fractional
part.

Random Number
Generator

FRAN (x)

FOCAL generates a random number. The value of x is ignored.

9Exponential

FEXP(x)

FOCAL generates e to- the power x.
(2.71828 X )

9Sine

FSIN(x)

FOCAL generates the sine of x in
radians.

9Cosine

FCOS(x)

FOCAL generates the cosine of x
in radians.

9Arctangent

FATN(x)

FOCAL generates the arctangent
of x in radians.

9Logarithm

FLOG(x)

FOCAL generates loge (x).

9 These are extended functions and may be chosen or deleted when
FOCAL is loaded.

9-92

Table 9-9.
Message
?OO.OO
?OO.OO

?01.40
?01.78
?01.96
?01.:5
?01.;4
?02.32
?02.52
?02.79
?03.05
?03.28
?04.39
?04.52
?04.60
?04.:3
?05.48
?06.06
?06.54
?07.22
?07.38
?07.:9
?07.;6
?08.47
?09.11
?10.:5
?11.35
?20.34
?23.36
?26.99
?28.73
?30.05
?31.<7
?30.71
?30.<0
?31.42
?31.43
?31.44

FOCAL Error Messages
Explanation

Manual start gjven from console.
Interrupt from keyboard via CTRLI C.
Illegal step or line number used.
Group number is too large.
Double periods found in a line number.
Line number is too large.
Group zero is an illegal line number.
Nonexistent group referenced by DO.
Nonexistent line referenced by DO.
Storage was filled by push-down list.
Nonexistent line used after GOTO or IF.
Illegal command used.
Left of= in error in FOR or SET.
Excess right terminators encountered.
Illegal terminator in FOR command.
Missing argument in display command.
Bad argument to MODIFY.
Illegal use of function or number.
Storage is filled by variables.
Operator missing in expression or double E.
No operator used before parenthesis.
No argument given after function call.
Illegal function name or double operators.
Parentheses do not match.
Bad argument in ERASE.
Storage was filled by text.
Input buffer has overflowed.
Logarithm of zero requested.
Literal number is too large.
Exponent is too large or negative.
Division by zero requested.
Imaginary square roots required.
Illegal character, unavailable command, or unavailable
function used.
Undefined library command.
Bad argument or missing argument to library command.
No such name in library directory.
Attempt to enter a duplicate name in the directory.
Library directory is full.

9-93

9-94

FORTRAN-D
FORTRAN-D compiles an,d runs programs written in the PDP-8
version of FOR~RAN II. Programs (usually created and stored
with the Symbolic Editor) are compiled in a single pass and executed (automatically) immediately following compilation.
Calling FORTRAN-D

To use FORTRAN-D, type:
.R FORT

FORTRAN requests the name of the input file, i.e., the file containing the FORTRAN program to be compiled and run. The user
responds with the file name and the RETURN key. FORTRAN
then requests the name of an output file in which to store the compiled version of the program. For normal usage, just the RETURN
key need by typed. FORTRAN places the compiled code in a file
of its own, then proceeds to run the program.
.
If a file name is entered for output, FORTRAN creates a permanent file in which the compiled binary program is saved. It is
then possible to rerun this program without recompiling it. To run
an already compiled program, call the FORTRAN operating system directly by typing:
.R FOSL

FOSL requests the name of an input file. Enter the name of the
file containing the compiled binary. For example, if the user types:
.R FORT
INPUT:MTRIX
OUTPUT:

FORTRAN compiles and executes the program MTRIX but does
not save the compiled binary.
FORTRAN compiles and executes the program MTRIX and
9-95

then leaves the compiled. binary in the file named. BMTRIX when
the user types:
.R FORT
INPUT:MTR1X
OUTPUT:BMT~lX

The FORTRAN binary program BMTRIX is executed without
first being compiled when the user types:
.R FCiSL

INPIJT:BMTRIX

All FORTRAN programs return to the Monitor when they have
completed execution.
Using FORTRAN-D
Differing versions of PDP-8 FORTRAN offer slightly different
features. FORTRAN-D differs in the way it is called into use
(described above), and in its more powerful I/O capability (described below). FORTRAN-D allows three data formats:
I
E
A

Integer format
Exponential format
Alpha format, ASCII value of a character is stored as an
integer value.

The standar~ device for READ and WRITE statements is the
Teletype, which is assigned device code 1. Because the Teletype
is so frequently ~sed, FORTRAN-D includes two special input/
output instructions, ACCEPT and TYPE. These instructions imply
use of the Teletype; therefore, the device code need not be specified.
ACCEPT is especially convenient if data is to be entered. at the keyboard because this instruction automatically supplies a line fe·ed
when the RETURN key is typed. Also, the user can correct an
erroneously typed value by striking the RUBOUT key.
A FORTRAN-D program can also utilize the high-speed reader
. and punch for I/O. These devices are assigned code 2. Because the
high-speed reader and punch are shared by all users, it is necessary
to assign them if they are to be used. Assign the appropriate devices
and mount tapes in the reader before running FORTRAN-D. An
9-96

automatic DEASSIGN is performed by FORTRAN before it returns to the Monitor; therefore, the user must reassign the devices
before each run.
FORTRAN.;D also allows programs to read and write data files
on the disk. These data files are completely separate from the program files. Data files are read and written by standard READ and
WRITE statements within the FORTRAN-D program. The device
code for the disk is 3. Because programs using the disk are treated
differently by FORT (the FORTRAN-D compiler), it is necessary
to identify programs which use the disk. These programs are identified by a DEFINE DISK statement as the first statement in any
such FORTRAN-D program including a READ or WRITE statement with device code 3.
Just as FORT itself must ask for the name of its input and output
files, so must a FORTRAN program ask for the names of its disk
files. FORTRAN-D programs do this by typing INPUT: and
OUTPUT: a second time. The user responds by typing the name
of the files to be read or written by the program. FORTRAN-D
asks for both input and output for all programs which include a
DEFINE DISK statement. If only input (or output) is to be used,
the user responds to the other by typing the RETURN key.
Line Format

FORTRAN programs consist of a series of lines, each a string
of 72 characters or less (the width of the Teletype paper from
margin to margin). Each line contains two fields: the first, which
begins at the left margin, is an identification field; the second contains the statement field. Termination of a line is indicated to the
computer by a carriage return, accomplished by typing the RETURN key.
The identification field can be blank and extends from the lefthand margin up to and including a semicolon character. This field
can contain one of the following types 'Of identification:
1. A Statement number. This number, which can be any positive integer from 1 to 2047 inclusive, identifies the statement on that line for reference by other parts of the program. Statement numbers are used for program control or
to assist the programmer in identifying segments of his
program.
9-97

2. The letter,. C. This identifies the
comment.

remaind~r

of the line as a

Although the identification field may be left blank, it cannot be
omitted entirely. The statement field begins immediately after a
blank space and extends through the next carriage return. A sample
FORTRAN program is shown below:
C
5
10
30
32
33
35
200
300
400

THIS PROGRAM CALCULATES FACTORIALS
TYPE 200
ACCEPT 300#N
I FACT= 1
IF (N-I> 5 1 32#33
TYPE 400#N#IFACT
GO TO 10
DO 35 l=l#N
IFACT=IFACT*I
CONTINUE
GO TO 32
FOR.'1AT (1# "PLEASE TYPE A POS I T I VE NUMBER" # I )
FORMAT (I)
FORMAT (/# 1#" FACTORIAL IS·· .. IFACT)
END

FORTRAN source programs are generated using the Symbolic
Editor Program. The Editor will facilitate formatting lines by use
of a tab character, .permittingautomatic movement to an indented
second field.
STATE~ENT NUMBERS
Each statement cart have a positive, nonzero integer (0-2047) as
its number. The statement number is used to reference that par. ticular statement elsewhere in a program. A statement number consists of one to four digits beginning at the left hand margin and is
followed by a semicolon. Statement numbers can be assigned nonsequentially; however, no two statements can have the same number. There must be no more than 40 statement numbers in a given
program, and they must have a value of 2047 (decimal) or less.
STATEMENT CONTINUATION CHARACTER
Frequently, a statement is too long to fit on one line. If the
character single quote (') appears as the last character of a line
before the carriage return, the next line ~s treated as a continuation
of the preceding statement. A statement may be continued on as
many lines as necessary to complete it, but the maximum number of
9-98

characters in the statement cannot exceed 128 (about two formatted lines). For example:
l~

A=H**2-(4.*A*C/(B**2+1.5*A*C»*4.3'
~B**2+«SQTF(C)*SQTF(D»/(B**2+1.5*A*C»

is e:quivalent to the formula:
A=B2-

- Although the continuation character, ('), allows a single statement to extend over two or more lines, no more than one statement
can be written on one line.
}'ORTRAN Statements
FORTRAN statements are of several types with various functions distinguished as follows:

1. Comment statements allow a programmer to insert notes
within the program.
2. Arithmetic statements resemble algebraic formulas. They
define calculations to be performed.
3. Control statements govern the sequence of statement execution within a program. These statements reference program line numbers.
4. Specification statements allocate data storage and specify
input/ output formats.
5. Input/output statements control the transfer of information
into and out of the computer.
COMMENT STATEMENTS
The character C, at the left margin of a line, designates that line
as a comment line. A comment has no effect upon the compilation
process but can serve as a guide to program logic for later debugging, etc. There is no limit to the number of comment lines which
can appear in a given program. A comment cannot be continued by
use of the continuation character, ('), but must be continued in a
second comment statement. For example:
C
C

THIS IS AN EXAMPL~
OF A COMMENT

9-99

CHARACTER SET
The following characters are used in the FORTRAN language:
1. The alphabetic characters, A through Z.
2. The numeric characters, 0 through 9.
3. The control characters:
semicolon
CR carriage return
period
LF line feed
single quote
(
left parenthesis
right p"arenthesis
" double quote
)
comma
4. The operators:
** exponentiation
/ division
+ addition
* multiplication
replacement
subtraction
All other characters are ignored by the Compiler except as
Hollerith information found in FORMAT statements (where all
Teletype chara(?ters are legal). The SPACE character has no
grammatical function (it is not a delimiter) except in FORMAT
stat~ments and can be used freely to make a program easier to
read.

CONSTANTS
Constants are explicit numeric values appearing in statements.
Two types of constants, integer and real, are permitted in FORTRAN.
Integer Constants
Integer (fixed-point) constants are represented by a string of
one to four decimal digits~ written with an optional sign and without a decimal point. An integer constant must fall within the' range
±2047. For example:
47
+47

( + sign is optional)

-2
0434
-0

(leading zeros are ignored)
(same as zero)
9-100

Real Constants
Real constants are represented by a digit string, an explicit decimal point, and are written with an optional sign. 1o Real constants
can also be written in exponential notation with an integer exponent
to denote a power of ten (i.e., 7.2 x loa is written 7.2E+3). A real
constant may consist of any number of digits but only the leftmost
six digits appear in the compiled program. Real constants must ,
fall within the range 0.14 x 10- 38 to 1.7 X 1038 • For example:
+4.50
4.50
-23.09
--3.0E14
7

(plus sign is optional)

(same as -3.0 x 1014 )
(saved as 7.00000, not the same as the integer. 7)

Fixed and Floating-Point Representation
The diffe.r:ence between integers and real numbers in FORTRAN
is the way in which each is represented in core memory. Both
types of numbers are' converted to binary to be stored in the computer.
A FORTRAN integer is stored in one 12-bit computer word.
The sign of the number is kept in the high-order bit and the
magnitUde (the integer value) in the remaining 11 bits. This representation, shown schematically in Figure 2-1,. is called fixed
point, because the decimal point is always considered to be to
the right of the rightmost digit. A FORTRAN integer may not
exceed the range of ± 2047. All integers greater than ± 2047 are
taken moaulo 2048 (i.e., 2049 is considered to be 1; 4099, to
be 3).
The floating-point format consists of two parts: an exponent
(or c:haracteristic) and a mantissa. The mantissa is a binary fraction with the radix point assumed to be to the left of bit one of
the mantissa. The mantissa is always normalized; meaning it is
stored with leading zeros eliminated so that the leftmost bit is
always significant. The exponent represents the power of two by
which the mantissa is multiplied to obtain the true value of the

----Where a number is to be identified as being negative, a minus sign (-)
10

must be used. A plus sign (+) is optional; with no sign, a number is considered positive.

9-101

number for use in computation. The. exponent and mantissa are
both stored in two's complement form.
SIGN

MAGNITUDE

FORTRAN INTEGER

SIGN OF EXPONENT

~
EXPONENT

11
SIGN OF
0
MANTISSA ...........
2.,~--~------------M-A-N-T-IS-S-A----------------~

o
3.

________________M_A_N_T_IS_S~A

________________

b. FLOATING POINT

Figure 9-1.

Number Represe!ltation

Users should not attempt to input floating point constants of
mor~ than six decimal digits, either in the FORTRAN source
program or via the run-time ACCEPT statement.
Integers cannot appear in floating-point expressions except as
exponent or subscripts. Some examples of illegal and legal expressions are as follows:
Expression

Legal

Mode

A(I)*B(J)**2
I(M) *K(N)
16.*B
(K+16)*3
A**(1+2)/B
8*A
4.*1
I+D

Yes
Yes
Yes
Yes
. Yes
No
No
No

Floating
Fixed
Floating
Fixed
Floating

VARIABLES
A variable is a symbol whose value may change during execution of a program. The name of a variable consists of one or more
alphanumeric characters, the first of which must be alphabetic.
9-102

Only the first four characters are interpreted as defining the variable name; the rest are ignored. For example, the name EPSILON
would be interpreted by the Compiler as EPSI. Since only the
first four characters are meaningful, the two names XSUM1 and
XSUM2 would be considered identical.
Spaces, as mentioned earlier, are ignored. The name EX IT
represents one variable, not two. Thus, EX IT, EXIT, or even
EXI T are identical names as far as the Compiler is. concerned,
and they all refer to the same numerical quantity.
The type (or mode) of a variable (integer or real) is determined
by the first letter of the variable name.
1. Integer variables begin with the letters:
I, J, K, L, M, or N
2. Real variables begin with any letter other than those above.
Variables of each type may be either scalar or array variables, as
explained below.
Integer Variables
Integer variables undergo arithmetic calculations with automatic
truncation of any fractional part. For example, if the current value
of K is 5 and the current value of J is 9, then J /K would yield 1
as a result.
Real Variables
A variable is real when its name begins with any character other
than I, J, K, L, M, or N. Real variables undergo no truncation in
arithmetic calculations. Real variables may be converted to integer
variables, and vice-versa, across an equal sign.
Scalar Variables
A scalar variable, which may be either integer or real, represents
a single number, as opposed to an array (below)- representing
a collection of numbers. For example, the following are scalar
variables:
LM

02
A
TOT AL

(considered to be TOT A by the computer)

J
9-103

Array Variables
An array variable represents a single element of a one-dimensional array of quantities. The variable is denoted by the array
name followed by a subscript enclosed in parentheses. The subscript may be any combination of integer variables and integer
constants forming a valid expression, as follows:
" (V)

(V+C)

(V-C)

(C)

where V is a fixed point (integer) variable, and C is a fixed-point
constant (not equal to 0).
The value of the expression in parentheses determines the referenced array element. For example, the row matrix, AI, would
be represented by the subscripted variable A ( 1 ), and the second
element in the row would be represented by A(2). Examples of
array variables are:
Legal Forms

Illegal Forms
A(2+1)

Y(1)

A(K+2)

B(C)

DIMENSION STATEMENT·
Array names must be identified as such to the FORTRAN Compiler. Two items of information must be provided in any program
usmg arrays:
1. Which are the subscripted variables?
. 2. What is the maximum value of the subscript?· (When an
array is used, a certain amount of storage space must be
set aside by the Compiler for the array elements.)
This information is provided by the DIMENSION statement:

where A and B are array names, and the integer constants 20 and·
15 ar:e the maximum dimensions of each subscript.
The rules governing the use of array variables and the DIMENSION statement are as follows:
1. All array names must appear in a DIMENSION statement.
9-104

2. DIMENSION statements may be used more than once
and may appear anywhere in the FORTRAN program,
provided that the DIMENSION of an array appears before any statement which references the array.
3. Any number of arrays can be defined in a single DIMENSION statement.
4. For notes on how to implement double subscripts (i.e.,
A(I,J», see the section on Implementation Notes.
Array variables may be either integer or real, depending upon
the initial letter of the array name.

DIMENSION

LIST(3~)~MAT(1~~)~REGR(2~)

In the statement above; the names LIST and MAT designate
integer arrays; that is, all elements of both arrays are integers.
The third name, REGR, designates a floating point, or real array.
The first array is a list containing a maximum of 30 elements;
the second array has a maximum of 100 elements.
The third array is a floating-point array and there are a maximum of 20 elements in it. Not all elements of an array need be
used in the course of a program; but, if using the DIMENSION
statement the variable LIST (3.1) could not be referenced without
the occurrence of an error message.
FORTRAN Arithmetic
ARITHMETIC OPERATORS
The arithmetic operators are symbols representing the common
arithmetic operations. The important rule about operators in the
FOR TRAN arithmetic expressions is that: every operation must
be explicitly represerit'ed by an operator. In particular, the multiplication sign must never be omitted. A symbol for exponentiation
is also provided since superscript notation is not available on a
Teletype.
Normally, a FORTRAN expression is evaluated from left to
right. like an algebraic formula. There are exceptions to this rule;
certain operations are always performed before others, regardless
of order. This priority of evaluation is as follows:

9-105

1.
2.
3.
4.
5.

( )

Expressions within parentheses
Unary minus
Exponentiation
Multiplication or Division
Addition or Subtraction

**
* or I
+or-

The term "binding strength" is frequently used to refer to the
relative position of an operator in a table such as the one above,
which is in order of descending binding strength. Thus, exponentiation has a greater binding strength than addition, and multiplicat;on and division have equal binding strength.
The unary minus is the arithmetic operator which indicates
that a quantity is less than zero, such as -53, -K, -12.3. It
refers only to the constant or variable which it precedes as opposed
to a binary operator, which refers to operands on either side of
itself as In the expression A-B. A unary minus is recognized by
the fact that it is preceded by another operator, not by an operand.
For example:
A

+ B**-2 I

C-D

The first minus sign (indicating a negative exponent) is unary;
the second (indicating subtraction) is binary. At present it is not
possible to raise an integer variable or integer constant to an
integer value with FORTRAN-D. Only real values can be raised
to integer powers.
The left-to-right rule can be stated more precisely: A sequence
of operations of equal binding streng~h is evaluated from left to
right. To change the order of evaluation, parentheses are required.
Thus. the expression A--B*C is evaluated as A-.(B*C), not
(A-B)*C. Examples of the left-to-right rule follow:
, The expression:

Is evaluated as:

(A/B)*C
(A/B)/C
(A**B)**C

A/B*C
AlBIA
A**B**C

'Use of Parentheses
Note the use of parentheses in the example below. They are
used to enclose the subscript of the dimensional variable, D; to
9-106

specify the order of operations of the expression involving A, B,
and C; and to enclose the argument of the function SINF.
D(I) + (A+B)**C + SINF (X)
In algebra there are several devices, such as square brackets [ ],
rococo brackets 1 etc., for distinguishing between levels when
expressions are nested. In FORTRAN, only the parentheses are
available, so the programmer must be especially careful to pair
parentheses properly. In any given expression, the number of
left parentheses must be equal to the number of right parentheses,
An easy way to check the proper pairing of parentheses is by
counting out, illustrated in the following example:
(Z+AM* (AM+1.) )/( (X**2+C**2)*P)
1
2
10 12
1 0
The procedure is this: Reading the expression from left to right,
assign the number, 1, to the first left par~nthesis (if you encounter
a right parenthesis first, the expression is already wrong). Increase
the count by one each time a left parenthesis is read, and decrease
the count by one when a right parenthesis is found. When the
expression has been completely scanned, the count should be zero.
If it becomes less than zero during the scanning, there are too
many right parentheses. If it is greater than zero at the end of an
exp.ression, there are excess left parentheses.

ARITHMETIC EXPRESSIONS
An algebraic formula such as:
Sa + 4b(x2

xu)

represents a relationship between symbols (a, b, x, xtJ and constants (S, 4, 2) indicated by mathematical functions and arithmetic
operators (+, -, multiplication, exponentiation). This same formula can be written as a FORTRAN arithmetic expression _with
very little change in appearance:
(S.*A + 4.*B* (X**2 - XZRO)
The construction of both expression~ is the same; the differences
are notational.
Elements of an arithmetic expression are of four types: constants, variables, operators, and functions. An expression may consist of a single constant or variable or a string of constants, variables, and functions connected by operators.
9-107

Examples of arithmetic expressions follow; each expression is
shown with its corresponding algebraic form.
Algebraic Expression

FORTRAN Expression

2v'X
3

2. *SQTF(X) /3.

3x1l" -2(x+y)
4.25

(3.*X*PI-2.* (X+Y) ) /4.25

a-sin 0 +2a cos(O -45)

A *SINF(THTA) +2. * A *COSF(THTA-0.78540)
(A**2-B**2) / (A+B)**2

ARITHMETIC STATEMENTS
The arithmetic statement relates a variable, V, to an arithmetic
expression, E, by means of the replacement operator, (=):
V-E
Such a statement looks like a mathematical equation, but is treated
differently. The equal sign is interpreted in a special sense; it does
not represent a relationship between left and right members, but
rather specifies an operation to be performed.
In an arithmetic statement, the value of the expression to the
right of the equal sign replaces the value of the variable on the left.
This means that the value of the left-hand variable will change
after the execution of an arithmetic statement. A few illustrations
of arithmetic statements are given below:
1.
2.
3.
4.
5.
6.

VMAX=VO+AXT
T = 2. *PI*SQTF( l./G)
PI = 3.14159
THTA= OMGA + ALPH*T* *2/2.
MIN=MINO
INDX = INDX + 2-

With the interpretation of the equal sign stated above, Example
6 becomes meaningful as an arithmetic statement. If, for example,
the value of INDX is 40 before the statement is executed, its value
will be 42 after execution.
9-108

In arithmetic expressions, a binary operator requires an operand
on its left and right. The equal sign of an arithmetic statement is
also considered to be a binary operator, as demonstrated in the
following revised table of operators:
Operator

Use

Interpretation

- (Unary)
**
*

-A
A**B
A*B

AlB

+
- (Binary)

A+B
A-B
A=B

negate A
raise A to the B th power
multiply A by B
divide A by B
add B to A
subtract B from A
replace the value of A with
the value of B

The replacement operator is considered to have the lowest binding strength of all the operators~ therefore, the expression on the
right is evaluated before the operation indicated by the egual sign
is performed.
Multiple Replacement
An important result of treating the equal sign as an operator is
that operations can be performed in sequence. Just as there can
be a series of additions, A+ B+C, there can also be· a series of
replacements:
A=B=C=D
Notice that because the operand to the left of an equal sign
must be a variable, only the rightmost operand, represented by D
in the example, may be an arithmetic expression. The statement is
interpreted as follows: "Let the value of the expression D replace
the value of the variable C, which then replaces the value of the
variable B" and so on. In other words, the value of the rightmost
expression is given to each of the variables in the string to the
left. A common use for this construction IS In setting up initial
values:
XZRO=SZRO=AXRO=O
T=Tl =T2=T3=60
P=FP=4. *ATM-AK
9-109

Only simple variables will compile correctly in this manner. For
example, statements of the type A( 1) =A(2) =R( 1) =0.123 are not
allowed and will not compile properly (subscripted variables may'
not be used in multiple replacement statements).
Multiple replacement done in a single statement must not contain
mixed mode variables. That is:
compiles correctly
compiles correctly
does not compile correctly

A=B=C=10
1=1-7
A=J=-7

Mode Conversion
Another useful result in treating the equ?l sign as an operator
is that the value of an expression on the right of an equal sign is
converted to the mode of the left-hand variable, if necessary, before
storage. For example:
A=lVl Stores the value of M as a floating-point number in A
K=B Stores the value of B (truncated) as an integer number in K

1f B = 4.75 and M
7, the conversion above will result in the
foHowing values being assigned:

A = 7.00000
K=4

FUNCTIONS
Functions are used in FORTRAN just as they are in ordinary
mathematics, acting as variables in arithmetic expressions. The
function name represents a call to a special subprogram which
performs the calculations to evaluate the function; the result is used
in the computation of the expression in which the function occurs. FORTRAN-D provides several mathematical functions:
square root, sine, cosine, arctangent, exponentiation, and natural
logarithm.
The argument of a function can be a simple variable, a· subscripted variable, or an expression. The argument must be in a
. floating-point format. FORTRAN recognizes a symbol as a function when it is a predefined symbol ending in F and followed by an
argume~t enclosed in parentheses (if the F is' missing from the
term, the symbol is treated as a subscripted variable). The argument of a function can consist of another function or groups of
functions. For example, the expression:
9-110

LOGF(SINF(X/2)/COSF(X/2) )
is equivalent to log

tan(

FORTRAN-D contains the following functions:
Meaning

Function Name
SQTF(X)
SINF(X)
COSF(X)
ATNF(X)
EXPF(X)
LOGF(X)

Square root of X
Sine of X, where X is
expressed in radians
Cosine of X, where X is
expressed in radians
Arctangent X, where X is
expressed in radians
Exponential of X
Logarithm of X

Program Control

In this section, FORTRAN statements are discussed in the context of program sequences. FORTRAN statements are executed
in the order in which they are written unless instructions are given
to the c,ontrary by use of the program control statements. These
statements allow the programmer to alter sequence, repeat sections,
suspend operations, or bring the program to a complete halt.
END STATEMENT
END occurs alone on a line and indicates the physical end of
the program to the FORTRAN Compiler. It can be preceded by a
line number. Every program must contain an END statement.
STOP STATEMENT
A program arranged so that the last written statement is the final
and only stopping place needs no other terminating indication; the
END statement automatically determines the final halt. Many programs, however, contain loops and .branches so that the last executed statement can be somewhere in the middle of the written
program. Frequently there is more than one stopping point. Such
terminations are indicated by the STOP statement. This causes
a final, complete halt; no further computation is possible, although
the program may be completely restarted from the beginning.
9-111

When a STOP is encountered during program execution, the
system signifies that a STOP has occurred by outputting an exclamation point (!) to the Teletype or high-speed punch, whichever is
being used as the output device.
PAUSE STATEMENT
The STOP statement prevents further coniputation after it has
been executed. There is a way, however, to suspend operation for
a time and then restart the program. This procedure is frequently
necessary when the user must do such tasks as loading and unloading paper tapes in the middle of a program. This kind of temporary
halt is provided by the PAUSE statement. The PAUSE statement
halts the program and returns control to the EduSystem 50 Monitor. The user may then perform any necessary manipulations and
restart the program by typing the Monitor command START.
GO TO STATEMENT
There are various ways in which program flow may be directed.
As shown schematically in Figure 9-2, a program may be a straightline sequence (1), or it may branch to an entirely different sequence (2), return to an earlier point. (3), or skip to a later point
( 4). The blocks represent sections of FORTRAN code. The lines
indicate the path which control takes as the program executes.

Figure 9-2.

Program Flow

9-112

All of these branches can be performed in several ways, the
simplest of which uses the statement:
GOTOn
where n is a statement number in the program. The use of this
statement is described in the following example, which also
illustrates the construction of a loop, the name given to program
branches of the type shown in the example above.
EXA1~PLE

OF INTEGER SUMMATION
In the following example, the sum of successive integers is
accumulated by repeated addition. The main computation is provided by the three-instruction loop beginning with Statement 2.
The statements preceding this loop provide the starting conditions,
called the initialization. The partial sum is set to zero, and the
first integer is given the value of one. The loop then adds the integer value to the partial sum, increments the integer, and repeats
the operation.
C
2

SUM DF FIRST N INTEGERS BY ITERATION
KSUM=0
INUM=!
KSUM=INUM+KSUM
INUM=INUM+l
GO TO 2
END

IF STATEMENT
The program shown in the preceding example performs the required computation, but note that the loop is endless. To get out
of th{: loop the user must know when to stop the iteration and
what to do afterwards.
The IF statement fills both requirements. It has the following
form:
IF(E) K,L,M
where E is any variable name, arithmetic expression, or arithmetic
statement, and K, L. and M are statement numbers. The statement :is interpreted in this way:
If the value of

E
E
E

< 0, GO TO statement K

= 0, GO TO statement L

> 0, GO TO statement M
9-113

Thus, the IF statement decides when to stop a loop by evaluating
an expression. It also provides program branch choices with the
transfer of control, depending on the results of the evaluation of E.
For example:
C
2
3

SUM OF THE FIRST 50 INTEGERS
KSUt1= 0
INUM= 1
KSUM=INUM+KSUM
INUM=INUM+l
IF (INUM-50)2 1 2 1 3
STOP
END

In the foregoing example, the initialization and mC}.in loop are
the same ~s for the example in Figure 9-2 except that the GO TO
staterpent of the earlier program has been replaced by an IF statement. The IF statement says., "if the value of the variable INUM
is less than, or equal to, 50 (which is the same as saying that if the
value of the expression INUM-50 is less than or equal to zero),
transfer control to Statement 2 and continue the computation. If
the value is greater than 50, stop." (See the section on Implementation Notes for an alternate solution.)
A loop may also be used to compute a series of values. The following illustration is an example of a program to generate terms in
the Fibonacci series of integers, in which each succeeding member of the series is the sum of the two members preceding it:
J

5
6

FIBONACCI SER'IESI 100 TERMS
DIMENSION FIB(100)
FIBC1>=1.0
FIB(2)=1.0
K=3
FIB(K)=FIB(K-l)+FIBCK-2)
K=K+ 1
IF CK-100)515iI0
STOP
END

In this program, the initialization includes a DIMENSION
statement which reserves spa<;e in storage, and two statements
which provide the starting values necessary to generate the series.
Each time a term is computed, the subscript is incremented so

9-114

that each succeeding term is stored in the next location of the table.
As soon as the subscript is greater than 100, the calculation stops.
DO LOOPS
Iterative procedures such as the program loop are so common
that a more concise way of presenting them is warranted. Three
statements are required to initialize the subscript, increment it,
and test for termination. The following type of statement combines
all these functions:
DO n l=Kl, K2, K3
here n is a statement number, I is a simple (non-subscripted)
integer variable, and Kl, K2, and K3 are simple integer variables
or integer constants which provide, in order, the initial value to
which 1 is set, the maximum value of I for which the loop will be
executed, and the amount by which 1 is incremented at each return
to the beginning of the loop. If K3 is omitted from the statement
it is assumed to be one (1). Statement n must be a CONTINUE
statement.

. 5

FIBONACCI SERIES~ 11210 TERMS
DIMENSION FIBCletet)
FIBCl)=l.f2I
FIB(2)=1.0
DO 5 K=3~ If2lf21
FIB(K)=FIB(K-l)+FlB{K-2>
CONTINUE
STOP
END

In words, the DO statement says "Execute all statements
through Statement 5 with K=3; when Statement 5 is encountered,
perform the following test: If K + 1 is less than or equal to 100,
set K:=K + 1 and continue the program by executing the first statement after the DO statement. If K + 1 is greater than 100, the next
sequential statement following Statement 5 is executed."
DO loops are commonly used in computations with subscripted
variables. In such cases, it is usually necessary to perform the
loops within loops. Such nesting of DO loops is permitted In
FORTRAN.
9-115

C
C
5
C
10

FIRST LOOP
DO 10 1= 1" 20
X(I)=0
NESTED LOOP FOLLOWS
DO 5 K=2" 40",2
X(I)=X(I)+B(K)-Z(K»**2
CONTINUE
END OF NESTED LOOP
A(I)=X(I)**2+C(I)
CONTINUE

Sequential elements in the array X(l) are formed by summing
the square of the difference of every second element in the Band
Z arrays. Then the array A(l) is formed by summing every element in the array C ( 1 ). and the square of every element in the
array X(l). The algebraic expression for the loop is as follows:
Ai=X1 2 :-

for i=1,2,3, ... 20

where

Xi= ~

(b k -zk )2

k=2

for k=2,4,6, .. .40

The following three rules about DO loops must be observed:
1. DO loops may be nested, but they may not overlap.
Nested loops may end on the same statement, but an
inner loop may not extend beyond the last statement of
an outer loop. Figures 9-3 schematically illustrates permitted and forbidden arrangements.

DOCE

DO
DO
DO
CONTINUE
CONTINUE
DO
DO
DO
CONTINUE

CONTINUE

CONTINUE
ILLEGAL NESTING
TECHNIQUES

CONTINUE
LEGAL NESTING
TECHNIQUES

Figure 9-3.

Legal and Illegal Nesting Techniques

9-116

2. If the user transfers into the range of a DO loop, the
value to be incremented (1, for example) is not autolllatically initialized as specified in the DO statement.
Transferring into the range of a DO loop is allowed as
long as:
a. Control was originally transferred out of the DO loop
by some means other than by completing it.
b. Incrementing and testing start with the current value of
I at the time control returns to the loop.
3. A DO loop must end on a CONTINUE statement.

DO
DO

CONTINUE

CONTINUE
CONTI NUE L - - , - - _

CONTINUE

ACCEPTABLE
BRANCHING

Figure 9-4.

ILLEGAL .
BRANCH ING

Program Branching in DO Loops

CONTINUE Statement
A special statement (CONTINUE) is provided which is not
an ex~cutable statement itself, but provides a termination for all DO
loops. DO loops must be terminated on a CONTINUE statement.
The CONTINUE statement is identified with the line number given
in the DO statement. For example:

IrO 37 MM= 11 1 fIj
IF (X(MM)-10f1j.)
CONTINUE
GO TO Iflj2
STOP

37 1 42 1 37

9-117

A single CONTINUE statement can be referenced more than
once in a single DO loop or can serve as the terminating line for
:
two or more nested DO loops.
COMPUTED GO TO
The GO TO statement previously described is unconditional and
provides no alternatives. The IF statement offers a maximum of
three branch points. One way of providing a greater number of
alternatives is by using the computed GO TO, which has the following form:
GO TO (Kl,K2,K3, ... ,Kn),J
where KII is statement number, and J is a simple integer variable,
which takes on values of 1,2,3, ... n according to the results of some
previous computation. For example:
IVAR=14*J/2+K
GO TO (5.1 7.1 5.1 7.1 5.1 7.1 10).1 I VAR

causes a branch to Statement 5 when IV AR= 1, 3, or 5; to Statement 7 when IV AR=2, 4, or 6; and to Statement 10 when
IVAR=7. When IVAR is less than 1 or greater than 7, the next
sequential statement after the GO TO is executed.

FORTRAN Input/ Output
So far, we 'have assumed that all information (programs, data,
and sub-programs) is in memory, withoul regard to how it is put
there. Programs are read by a special loader, but the programmer
is responsible for the input of data and the output of results by
including directions for I/O operations in his program.
For any input/output procedure, several questions must be
answered:
1. In which direction is the data going? The data coming in
is being read into memory; information going out is being
written on whatever medium is specified.
2. Which device is being used? Information may be transferred between core and whatever input/output devices
are available; each 1/0 operation must specify the device
involved.

9-118

3. Where in core memory is the data coming from or going
to? The amount of oata and its location in the computer
storage must be specified.
4. In what mode is the data represented? In addition to
floating and fixed-point modes for numeric data, there
is the Hollerith mode for transferring alphanumeric or
text information.
5. What is the arrangement of the data? The format of incoming or outgoing data must be specified.
For every data transfer between core memory and an external
device, two statements are required to provide all of the information listed above. The first three items are specified by the input/
output statement, and the last two items are determined by the
FORMAT statement.
DAT A FORMATS
. FORTRAN-D provides for communication of data to and from
a program in the fol1owing ways:
ASCII Coded Data
The Teletype can be used to transfer data to the program
either via the keyboard (in which case the user types the data)
or from previously punched paper tape (read via the Teletype
tape reader). Data can be output from a program to the Teletype, producing a printed copy with or without the corresponding
punched paper tape. The high-speed reader and punch can also
be used for data transfer via punched paper tape. No printed
copy is made when output is to the high-speed punch.
Binary.Coded Data
Disk and DECtape can also be used for data transfer, in which
case the data is stored as a core image on tape in 128-word
blocks of 12-bit binary words. Integers are read and written as
single 12-bit words, floating-point numbers as three words. Alphanumeric information is transmitted as 8-bit ASCII coded characters right-justified in 12-bit words (one character per word).
INPUT/OUTPUT STATEMENTS
Input/Output statements control the transfer of information. As
illustrated below, I/O statements consist of three basic items of
information: the device being accessed and the direction of transfer,
9-119

the number of the FORMAT statement controlling the arrangement
of data, and the list of variable names whose values are to be
output or changed by new input.
. NOTE
There is a restriction on subscripted variables when used with I/O statements. Subscripts to be used with· I/O statements
must be of the form: LL" where each L is
a letter, and not of the form LD, where
D is a digit. For example:

DO 10 Ll=1,4
ACCEPT 7,A(L1)
will not store information correctly. 'The
statement should read:
DO 10 LL=1,4
ACCEPT 7,A(LL)
ACCEPT N,V(l),V(I+1),V*1+2
\

=y-

t List of variable
names
1 - - Statement number of
FORMAT statement
Device Selection and direction of
transfer
ACCEPT and TYPE Statements
,
ACCEPT and TYPE transfer information between the Teletype and EduSystem 50. ACCEPT causes information to be read
into core memory from either the keyboard, the Teletype paper
tape reader, or the high-speed reader if it is assigned before calling
FORTRAN-D. ACCEPT is especially convenient if data is to be
entered at the keyboard since it automatically supplies line feed
when the RETURN key is typ~d. Also,. the user may correct an
erroneously typed value by typing the RUB OUT key.
TYPE causes information to be transferred from core memory
to the Teletype printer, the Teletype paper tape punch, or the
high-speed punch if it is assigned before calling FORTRAN.;.D.
9-120

If the user needs the high-speed reader and punch for I/O, he
must assign the devices for his use before calling the FORTRAN
compiler (FORT) or operating system (FOSL). Once logged into
EduSystem 50, he replies to Monitor's dot with the appropriate
assign statements. For example:
.ASSI GN P
'p ASSIGNED

.ASSIGN R
R ASSIGNED

The Monitor replies with P ASSIGNED and R ASSIGNED in
re:sponse to the user. If the device requested is not available (being
used by someone else), Monitor replies JOB XX HAS X, where
XX is the job number assigned the device X. The high-speed
reader/punch is device code 2. If running several programs, the
user should reassign the devices before each run.
READ and WRITE Statements
EduSystem 50 FORTRAN also allows programs to read and
write data files on disk. These data files are completely separate
from program files. Data files are read and written by standard
READ and WRITE statements within the FORTRAN program.
The device code for the disk is 3. Since programs which use disk
are treated differently by FORT from those which do not use disk,
it is necessary to identify programs which do. This is done by
placing a DEFINE DISK statement as the first statement in any
FORTRAN program which includes a READ or WRITE statement with a device code of 3.
Just as FORT must ask for the names of its input and output
files~ so must a FORTRAN program ask for the names of its disk
files. FORTRAN programs do this by typing INPUT: and OUTPUT: a second time. The user responds by typing the names of
the data files to be read or written by the program. FORTRAN
will ask for both INPUT and OUTPUT for all programs which
•
include a DEFINE DISK statement. If only one is to be used,
respond to the other by typing the RETURN key.
VARIABLE SPECIFICATION IN I/O STATEMENTS
Following the instruction that selects the device and direction of
transfer is the statement number of the FORMAT statement that
9-121

controls the arrangement of the information being transferred. For
example:
ACCEPT 10 .. A
10

FORMAT

(E)

Every I/O statement must have a reference to a FORMAT statement.
The final item specified in the I/O statement is the list of
. variables. This is a sequential list of the names of variables and
. array elements whose values are to be transferred in the order indicated. There is no restriction on"the number of names which may
appear in the list of an I/O statement, as long as the total statement length does not exceed 128 ·characters. The modes of the
variables named 'need not agree with the corresponding FORMAT
statement; however, the modes specified in the FORMAT statement take precedence. For example, where A=3.2, J-:27, KAL=
302, and BOB=7.58:

TYPE 23 .. A.. J .. KAL .. BOB
FORMAT (I .. E.. I .. E)

The decimal portion of A is dropped and the number 3 is
printed as an integer; the value of J is printed as a normalized
number; KAL is printed as an integer; and ,BOB is printed as a
normalized number. The output would look like the following:
+ 3

+0.270000E+2

302

+0.758000E+01

.NOTE
In READ and ACCEPT statements~ although the number is read according to the
FORMA Tstatement, it is stored according
to the mode of the variable. For example:
5

l~,A

FORMAT

(1)

causes. the number 12.3 typed by the user
to be read as 12 and stored as 0.120000E+2 ..
9-122

Array names included in I/O lists must be subscripted in one
of the following forms:
A(V)

A(V+C)

A(V-C)

A(C)

where A is the array name, V is a simple integer variable and C
is a positive nonzero integer constant.

TYPE10IAIIIBIC(I+I>IN(J+I>
FORMAT (EII1E1 />

If the list contains more names than there are elements in the
FORMAT statement, the FORMAT statement is reinitialized when
the elements are exhausted. The first element in the FORMAT
state:ment then corresponds to the next name in the list. For instance, in the preceding example when the value of the variable, B,
is printed in the E format, the control character, slash (/), causes
a carriage return/line feed to occur. Then the FORMAT statement
is reinitialized, and the array element, C(I+K), is printed in the E
format and the array element N(J+L) in the I format.
The list does not have to exhaust the elements of a FORMAT
statement. If there are fewer names in the list than there are elements in the FORMAT statement, the program completes the I/O
operation and proceeds to the next sequential FORTRAN statement. If this next statement is another I/O statement that references
a previously unexhausted FORMAT statement, that FORMAT
statement is reinitialized. FORMAT statements are reinitialized
when they are referenced or when all of their elements are exhausted.

FORMAT STATEMENT
The FORMAT statement controls the arrangement and mode
of the information being transferred. The values of names appearing in the I/O statement list are transferred in the mode specified
by the corresponding element in the FORMAT statement. These
controlling elements consist of the characters E, I, A, slash (/),
9-123

and quote ("). The set of elements must be enclosed in parentheses
and separated by commas. For example:
FORMAT

(AI

E" 11'" "HOLLERI TH")

The control elements E and I are used for defining the mode of
the data being transferred. When a variable is transferred in the E
format, it is stored or output in floating-point form. If the variable
is transferred in the I format, it is stored. or output in fixed-point
or integer form. Mode conversion on input or output can be accomplished because the elements in the FORMAT statement define
the mode of the data. The mode of the original variable is overridden where necessary. For example:
i0

TYPE 10"A
FORMAT ( I )

The variable, A, is printed as an integer, and the fractional part
of A is truncated. If A has a value of 14.96, only the integer part,
14, is printed. If A has an absolute value of less than one, zero is
printed.
THE A FORMAT SPECIFICATION
The control element, A, is used for defining the alphanumeric
mode of data I/O. When a variable is to be assigned an alphanumeric value, data is read one character per variable. FORTRAN
ignores CTRL/C, blank tape, RUBOUT, and 0200 code (leader/
trailer tape) . FORTRAN does not see the form-feed character
when input is from the disk. The decimal equivalent of the ASCII
value of the character is assigned to the variable. For example: .
A

= 301

(ASCII)

= 192 (decimal)

Any variable assigned the. alphanumeric value, A, would be set
equal to 192.
It is possible to do arithmetic with integer variables assigned
alphanumeric values. For. example:

10
12

DO 10 J= 1" 5
ACCEPT 12" KCJ>
IF CKCJ)-141> 10,,40,,100
CONTINUE
FORMATCA)

9-124

where the IF statement tests to see if the last character read is a
carriage return (which is ASCII 215 or 141 decimal); if so, control transfers to Statement 40; if not, control stays within the DO
loop.
It is not possible to do arithmetic with real variables assigned
alphanumeric values. Output in alphanumeric format converts the
value of the variable into an ASCII character and prints that charactt~r. For example:
12

FORMATCA)
DO 20 I = I" 5
TYPE 12" A(J)
CONT INUE

If the variables A (1) through A (5) were not originally assigned
alphanumeric values, the results of the output can be meaningless.

INPUT FORMATS
Input data words can only consist of a sign, a decimal value, an
exponent value if the data is floating-point, and' a field terminating
character such as space. Any character that is not a number,
decimal point, sign, or E can be used to terminate a field except
the RUBOUT character. When typing data, any number of spaces
or other nonnumeric characters can be typed before the sign or
decimal value in order to make the hard copy more readable.
Input data can be transferred into core memory from either the
Teletype paper-tape reader, the keyboard, the high-speed reader,
or DECtape. Input can be entered in either fixed- or floating-point
modes (integers or decimal numbers). The mode in which data is
stored in core memory is controlled by the first letter of the variable name. The characters read into core are determined by the
corresponding element in the FORMAT statement.
Integer Values-the I Format
An integer data field consists of sign l l and up to six decimal
characters. Some examples of integer values are as follows:
11 Plus sign can be represented by a plus or space character. Minus is
represented by a minus character. If a sign character is absent from the
data word, the data is stored as positive.

9-125

Typed Numbers

Values Accepted

-2001
-40
-0040
16
-2041

-2001
-0040
-0040
0016
2047

Real Values-the E Format
A floating-point input word consists of a sign, the data value up
to six decimal characters, an E if an exponent is to be included, the
sign of the exponent, and the exponent (i.e., the power of ten by
which the data word is multiplied). For example:
ddd.dddEnn
The d's represent numerical characters in the data and the n's
represent the 2-digit power of ten of the exponent (preceded by a
sign). Either the sign, the decimal point, or the entire exponent
part can be omitted. If the sign is omitted, the number is assumed
to be positive; if the decimal point is omitted, it is assumed to appear after the rightmost decimal character. If the exponent IS
omitted, the power of ten is taken as zero.
Some examples of floating-point values are as follows:
Typed Numbers

Values Accepted

16.
.16E02
1600.E-02

0.16 x 10:!
0.16 X 102
0.16 X to:!

OUTPUT FORMATS
E and I Formats
Integer values are always printed as the sign and 'a maximum
number of four cha~acters with spaces replacing leading zeros. On
output, integers are left justified within the stated field. Sufficient
trailing spaces are printed to fill the field followed by one additional
space.
Floating-point values are printed in a floating-point format which
consists of sign, leading zero, decimal point, six decimal characters,
the character E, the sign of the exponent (minus or plus), and an
exponent value of two characters. For example:

9-126

Integer Values

Output Format

-1043
-0016
+0016

-1043
16
+ 16

Floating-point values are printed as follows:
SO.ddddddEsnn
where: S represents the sign, minus sign, or space
dddddd represents six decimal digits of the data word
E indicates exponential representation
s represents the sign of the exponent value
nn represents the exponent value
Some examples of floating-point output are:
Decimal Value

Output Format

-8,388,608.0
-.000119209

-0.8388608E+07
0.119209E-03

FORMAT Control Specifications
In most cases when data is to be presented, it must be labeled
and arranged properly on a data sheet. ]n order that this can be
accomplished with FORTRAN-, a provision has been made so that
text information and spacing can be printed along with the data
words. These features are provided by the special FORMAT control elements quote (") and slash (/). The slash character causes
a return to the left margin.
Hollerith Output
When text information is enclosed in quotes and is contained as
part of a FORMAT statement, it is output to the specified device
as it appears in the statement. This output occurs when a TYPE
or WRITE statement references a FORMAT statement containing
text, and all other elements of the FORMAT statement previous to
the text have been used. All legal Teletype characters (other than
the quote character itself) can be contained within quotes and output as text.
9-127

TYPE 10
FORMAT(/,,"THIS IS HOLLERITH""/)

100

TYPE 100"AMIN"AMAX
FORMAT (I" "MIN IMUM="" E" I" "MAXIMUM="" E" I)

210

250

TYPE 210
FORMAT(/"I,,"
CUMULATIVE DISTRIBUTION""I"I'
..
INCREMENTS
FREQUENCY"" I)
DO 220 K=I" 100
TYPE 250"K"VALUCL)"VALU(K+l)"COUNT(K)
CONTINUE
FORMAT (I" .... "E" .. ""E"/)

Implementation Notes

DOUBLE SUBSCRIPTS
This version of FORTRAN does not have the facility for doublesUbscripted variables. To accomplish dO,uble subscripting, the pro- ,
grammer has to include indexing statements in the source program
as illustrated below. In this example, the matrices are stored columnwise in memory; that is, sequential locations in memory are
used as follows:
Relative Position
in Memory (1NDX)
Element
all
a21
a31
a41
a51
a61

I
2
3
4
5
6

a12
a22

7
8

a56
a66

35
36

If referencing Element a56 in the array, M=5, N=6, (1=6 for
a 6 by 6 array), and INDX=M+1*(N-1)=S+I*5=35. If ref-

erencing Element a22, INDX=2+6* 1=8.
9-128

C
C

MATRIX MULTIPLY PROGRAM
DIMENSION A(36)IB(36)IC(36)
ACCEPT DIMEl'.JSION OF ARRAY
ACCEPT III
FORMAT ( I )
DO 10 M= 1 I I
DO 10 N= 1 # I
I N DX =M+ I (N - 1 )
ACCEPT FIRST MATRIX

ACCEPT
2
10
15

C
20
C

30
C

40
21

I~A(INDX)

FORMAT(E)
CONTINUE
TYPE 15
FORHAT(/I/#/)
DO 20 t1= 11 I
DO 20 N=111
INDX=M+U(N-l)
~CCEPT SECOND MATRIX
ACCEPT IIB(INDX)
C ( IN DX) =QJ
CONTINUE
MULTIPLY MATRICES
DO 30 M=I,1
DO 30 N= 1 I I
DO 30 K=I,I
IC=N+I*U1-1 )
IA=K+l*(:1-1>
I B= K+ 1 * (K- 1 )
C(IC)=C(lC)+A(IA)*B(IB)
CONTINUE
TYPE 15
PRINT RESULTS IN MATRIX
TYPE 21
DO 40 i1= 1 # I
TYPE 21
DO 40 N= 1, 1
IN DX= N+ I * (11- 1 )
TYPE 11 C (INDX)
CONTINUE
FORMAT (/)
TYPE 15
END

FOP~

SUBSTATEMENT FEATURE
The most important result of treating the equal sign as a binary
operator (as explained in the section on Arithmetic Statements)
is that it may be used more than once in arithmetic statement. In
addition to simple replacement operations (see section on Multiple
Replacement), consider the following;
CPRM = (CKL - CKG) / (CPG = P*(Q-I-l))
9-129

The internal arithmetic statement (or substatement). CPG p*
(Q+ 1). is set off from the rest of the statement by parentheses.
The complete statement isa concise way of expressing. the following
common type of mathematical procedure:
Cl

Let:

-C 1i/.;,

Cpg

Where: C v!;'

= p.(q+1) .

The stating of a relation followed by the conditions for evaluating any of the variables can be expressed in a single arithmetic
statement in FORTRAN.
A second use of the equal sign is shown below. For background
on this short program, see the discussion of the same problem in
the section on the IF statement.
C

SUM OF THE FIRST 50 INTEGERS'
KSUM=0
INUM 50
KSUM=INUM+KSUM
I F ( IN UM + IN UM - 1 ) 3" 3.1 2
STOP

2
3

In this example, the sum is formed by counting down, but the
same results are achieved as in the section on the IF statement.
The initialization is changed so that INUM starts with the value of
50 instead of 0, and the statement, INUM=INUM+ 1, is no longer
required.
ERROR CHECKING
Because of the extremely compact nature of the FORTRAN-D
Compiler, either FORTRAN features or error checking will suffer.
In the case of FORTRAN-D, checking for .certain errors is not as
important as preserving the language. Therefore, the programmer
is advised to follow the rules as stated in this manual and carefully
check his program for mistakes. For example, the statement
A

C -

will compile, although at execution time it will give unpredictable
results.

9-130

It should be noted that data areas must not extend below loca-

tion 5600 in FORTRAN-D. No diagnostic is issued unless program
and data areas actually overlap. A maximum of 89610 words- are
available for data. Care should be taken not to exceed the limits
through use of large arrays, etc. Similar obvious errors are accepted
by the Compiler; their effects are often unpredictable.
FORTRAN-D SOURCE PROGRAM RESTRICTIONS
The following limits are imposed upon all FORTRAN-D source
programs:
1. Not more than 896 data cells. This includes all dimensional variables, user-defined variables, constants, and all
constants generated by the usage of a DO loop.
2. Not more than 20 undefined forward references to unique
statement numbers per program. An undefined forward
reference is a reference to any statement label that has
not previously occurred in the program. Multiple refer- ences to the same undefined statement numbers are considered as one reference.
3. Not more than 64 different variable names per program.
4. Not more than 128 characters per input statement.
5. Not more than 40 numbered statements per program.
FORTRAN-D COMPILER AND OPERATING SYSTEM
CORE MAP
The Compiler occupies the following core locations:
0003-7600
7200-7600

Compiler plus tables
Compiler tables (undefined forward reference tables, etc.)

The Operating System occupies locations:
0000-5200
0000-6000

Operating System for paper I/O
Operating System for disk I/O

Locations 5201 through 7576 are available for the user's program when using paper tape input/output.
9-:131

Table 9-10.

FORTRAN-D Statement Summary

Statement and Form

Explanation

Arithmetic StatemenJs
v=e

v is a variable (possibly subscripted); e is
an expression.

Control Statements
GO TO n

n is a statement number.

GO TO (n 1 ,n2, ... ,n ll ),i

nl, ... ,nn are statement numbers; i is a nonsubscripted integer variable.

IF (e) nl,n2,rl 3

e is an expression; nl,n2,n 3 are statement
numbers.

DO n i=k b k 2 ,k a

n is the statement number of a CONTINUE; i is an integer variable; k 1 ,k 2,k B
are integers or nonsubscripted integer variables.

CONTINUE

Proceed

PAUSE

Temporarily suspend execution.

STOP

Terminate execution.

END

'Terminate compilation; last statement
program.

III

Specification Statements
DIMENSION v1(n 1 ),
v2(n2) ,... ,vn (nn)

Vl, ... ,vn are variable names; nl, ... ,nn are
integers.

DEFINE device

Device is DISK or TAPE.
s is a data field specification.

COMMENT

Designated by C as first character on line.

Input/ Output Statements
ACCEPT f, list

f is a FORMAT statement number; list is
a list of variables; input is from the Teletype.

TYPE f, list

f is a FORMAT statement number; list is
a list of variables; output is to the Teletype.
9~132

Table 9-10 (Cont.).

FORTRAN-D Statement Summary

Statement and Form

Explanation

READ u,f, list

u is an integer representing the device
which data is to be read: 1=Teletype, 2=
high-speed reader, 3=disk; f is a FORMAT
statement number; list is a list of variables.

WRITE u,f, list

u is an integer representing
which data will be written:
2=high-speed punch, 3=disk,
MAT statement number; list
variables.

device onto
1=Teletype,
f is a FORis a list of

FORTRAN-D Error Diagnostics
Diagnostic procedures are provided in the Compiler to assist the
programmer in program compilation. When the compiler detects
errors in a FORTRAN source program, it prints the error messages on the user termimil. These messages indicate the source of
the errors and direct the programmer's efforts to correct them. To
speed up the Compiler process, the Compiler prints only an error
code. The programmer then looks up the error message corresponding to the code in Tables 9-11 through 9-13 and takes the appropriate corrective measures.
COMPILER COMPILATION DIAGNOSTICS
Format of Diagnostics

xxxx

The identifying condition
code

'----The number of statements since the appearance of a n\1mbered statement (octal
value).
L..--....;The statement number of the last numbered statement.
9-133

For example:
10

A=I(.J+l)
H=A*(H+SINF(THTA)

.During compilation of the prevIOUS statements, the following
error code would be printed:
1:,1 0 1

indicating that a statement which occurs one statement octal. (one
decimal) after the appearance of Statement 10 is in error. The
message corresponding to Code 11 shows that the number of left
and right parentheses in the statement is not equal.
If a statement number is referenced but does not appear in the
source program, the diagnostic code will be printed as follows:
xxxx

where the number usually reserved for the last numbered statement
(xxxx) is replaced by the missing statement, e.g.
GO TO

lCilCil

The diagnostic would appear as follows where Statement 100 is
never defined.
IV'lCi'l

~Iil

Table 9·11.
Error
Code
00
01

03
04
05
06
07
)0
).)

FORTRAN·D Compiler Compilation Diagnostics
Explanation

Mixed mode arithmetic expression
Missing variable or constant in arithmetic expression
Comma was found in arithmetic expression
Too many operators in this expression
Function argument is in fixed-point mode
Floating-point variable used as a subscript
Too many variable names in this program
Program too large, core storage exceeded
Unbalanced right and left parentheses

9-134

Table 9-11 (Cont.).

F'ORTRAN-D Compiler Compilation Diagnostics

-----------------------------------------------------Error
Code

Explanation

13
14

Compiler cQuld not identify this statement
More than one statement with same statement number
Subscripted variable did not appear in a DIMENSION
statement
Statement too long to process
Floating-point operand should have been fixed-point
Undefined statement number
Too many numbered statements in this program
Too many parentheses in this statement
Too many statements have been referenced before they
appear in the program
DEFINE statement was preceded by some executable
statement
Statement does not begin with a space, tab, C, or number

------------------------------------------------------12
. Illegal character found in this statement
15

17
20
21
22
23
25

-------------------------------------------------------COJvlPILER SYSTEMS DIAGNOSTICS
Certain errors can make it impossible for the Compiler to proceed in the normal manner. These errors occur before the Compiler has been loaded into core. They may be caused by improperly loading the Compiler, by not having an END statement on a
source file, bya machine malfunction, or by other errors. These
errors, referred to as system errors, are explained in Table 9-12.
Table. 9-12..
Error
Code
0240
3100

3417
6145
6223
6226

6257
6724

6746
7114

FORTRAN-D Compiler Systems Diagnostics
Explanation

System file error. One of the FORTRAN components cannot be found or the disk is full, preventing FORTRAN
from proceeding. Try recalling FORT.
Illegal operator on compiler stack.
Preprecedence error.
Could not find FOSL on system device; if the error occurs,
it may be necessary to reload FORT and FOSL.
Error: while loading the Compiler.
Same as above.
Same as above.
No END statement on source device.
Same as above.
Same as above.

9-135

OPERATING SYSTEM DIAGNOSTICS
Not all errors are detected by the Compiler. Some errors can
only be detected by the operating system (FOSL). Also there are .
some conditions which indicate errors on the part of the Compiler
and/ or operating system. When such an error occurs during running of a program, the computer. prints out an error message containing the word TILT or ERROR and an error number. The
computer then halts. If the CONTINUE switch is pressed, the computer takes the action listed in Table 9-13.
Table 9·13.

FORTRAN·D Operating System Diagnostics

ErrQr
CQde

ExplanatiQn

01
02
04
05
06
11
12
13
14
15
16
17
20
21
22
40
41
76
77

Checksum'errQr Qn FORTRAN binary input
Illegal Qrigin Qr data address Qn FORTRAN binary input
Disk input-Qutputerrorl2
High-speed reader errQr
Illegal FORTRAN binary input device
Attempt to' divide by zero
FIQating-PQint input data conversiQn error
Illegal QP cQde
Disk input-Qutput error1,2
NQn-FORMAT statement used as a FORMAT
Illegal FORMAT specification
FIQating-PQint number larger than 2047
Square rQQt Qf a negative number
EXPQnential negative number
LQgarithm Qf a number less than O'r equal to' zerO'
Illegal device code used in READ Qr WRITE statement
System ,device full, eQuId nQt cQmplete a WRITE statement
Stack underflO'w errQr13
Stack Qverflow errQr13

May be caused by machine malfunction or operating system error.
May be caused by source program or loading error; to correct, do the
following in descending order.
a. Use Diagnose to determine where the error occurred.
h. Recompile the source program.
c. Examine source program (in particular the arithmetic statements
and subscripted variables).
12
13

9-136

PAL-D ASSEMBLER
IlIltroduction
The EduSystem 50 Assembly System is composed of the PAL-D
Symbolic Assembler, LOADER, and ODT. The PAL-D Assembler is used to translate the user's source program into an object
program (binary or machine code). LOADER is used to transfer
the user's object program from the disk into core for debugging
or execution. ODT (Octal Debugging Technique) is used to dynamically debug the object program which has been loaded into
core using LOADER.
The PAL-D Assembler is fully documented in Programming
Languages 1972, Chapter 14. PAL-D source programs are usually
written on-line using the EDIT program, which stores them in
disk files. The Assembler checks for assembly language syntax
errors and for undefined user symbols. To call the PAL-D Assembler, the user types:
.R PALD

PAL-D responds by requesting INPUT: Type the name of the
source program or programs to be assembled. A maximum of
three files can be assembled together. PAL ... D then requests OUTPUT: Type the name of the new file in which PAL-D will store the
assembled program in executable binary form. PAL-D then requests OPTION: For a normal assembly, press the RETURN key.
If an assembly listing is not desired, respond to OPTION with N.
PAL-D then proceeds to assemble the program: any errors
in the program are indicated; the program symbol table is printed;
and finally, an assembly listing of the source program is printed.
When the listing is completed and the assembly finished, ~ontrol
is returned to the Monitor.

EduSystem 50 PAL-D
Because of the necessary hardware changes made for timesharing on EduSystem 50, PAL-D has been revised in the following ways (as differing from PAL-D on a non-timeshared
PDP-8) :
A. P AL-D, under EduSystem 50, allows 245 (decimal) user
symbols in addition to the permanent symbols listed in

9-137

Table 9-14. Allsymt>ols reside in locations 5200 through
7777. The permanent s·ymbol table has beeR revised to
include all instructions peculiar to the time-sharing system.
B. A CTRL/C (tC) from the ·Teletype terminates the assembly, and halts.PAL-D, sending the user back to the Monitor.
Example of a PAL-D Program
.R PALD
INPUT:TYPE2
OUTPUT: B IN2
OPT IO~:
COt:NT
CRLF

Leep
OUT

REG
START

·0415
0417
0406
0425
0416
0400
/PROGRAM TO
*0400
START,
CLA
JMS
TAD
DCA
TAD
DCA
LOOP,
TAD
JMS
ISZ
ISZ
JMP
Jr.-'s
HLT
COU:\JT,
0
REG,
0

0400
0401
041iJ2
0403
0404
0/.105
0406
0407
0410
0Lll1
011 12
0413
01114
0415
0416

7200
4217
1377
3215
1376
3216
1216
4225
2216
2215
5206
4217
7402
0000
0000

0417
0420
0421
0422
0/123
0424

0000
1375
4225
1374
4225
5617

CRLF,

0425
0426
01127
0430
0431
0432
0574
0575
0576
0577

0000
6046
6041
5227
7200
5625
0212
0215
0260
7766

OUT,

TY·PE OUT "0123456789"
CRLF
( - 1 2'>
COUNT
(260 )
REG
REG
OUT
REG
COUNT
LOOP
CRLF"

0
TAD (215)
JMS OUT
TAD (212)
J~S OUT
JMP I CRLF
0
TLS
TSF
JMP .-1
CLA
JMP I OUT

ISS

9-138

/ASC I I CODE FOR ZERO (0 )

/ASC I I FOR CARRIAGE RETUR:\J
/LINE FEED

Table 9-14.

Mnemonic

Code

EduSystem SO Symbol List

Operation

Event Time

Memory Reference Instructions
AND
0000 Logical AND
TAD
1000 Twos complement add
ISZ
2000 Increment & skip if zero
3000 Deposit & Clear AC .
DCA
JMS
4000 Jump to subroutine
JMP
5000 Jump
GlrOUP 1 Operate Microinstructions
NOP
7000 No operation
lAC
7001 Increment AC
RAL
7004 Rotate AC & link left one
RTL
7006 Rotate AC & link left two
RAJ{
7010 Rotate AC & link right one
RTR
7012 Rotate AC & link right two
CML
7020 Complement link
CMA
7040 Complement AC
CLL
7100 Clear link
CLA
7200 Clear AC
Group 2 Operate Microinstructions
.HLT
7402 Halts the computer
05T
7404 Inclusive OR switch register
with AC
SKP
7410 Skip unconditionally
SNL
7420 Skip on nonzero link
SZL
7430 Skip on zero link
SZA
7440 Skip on zero AC
SNA
7450 Skip on nonzero AC
SMA
7500 Skip on minus AC
SPA
7510 Skip on plus AC (zero is positive)
Combined Operate Microinstructions
CIA
7041 Complement & increment AC
STL
7120 Set link to 1
GLK
7204 Get link (put link in AC, bit 11)
STA
7140 Set AC=-1
LAS
7604 Load AC with switch register
PSEUDO-OPERATORS
DECIMAL
OCTAL
EXPUNGE
PAGE
FIELD
PAUSE
FIXTAB
TEXT
I
XLIST

9-139

3
3
3
3
3
2
2
1

1
4
3
1
1
1
1
1
1
1
1
1,

1
1
1

Table 9-14 (Cont.).
Mnemonic

Code

EduSystem 50 Symbol List
Event Time

Operation

lOT Microinstructions
PROGRAM INTERRUPT
lOT
6000 (See Introduction to Programming
1972, Chapter 6.)
KEYBOARD READER
KSF
6031 Skip if keyboard/ reader flag
1
KCC
6032 Clear AC & keyboard/reader flag
KRS
6034 Read keyboard/ reader buffer
KRB
6036, Clear AC & read'keyboard buffer,
& clear keyboard flag
6400 Set keyboard break
KSB
6401 Set buffer control flags
SBC
6030 Read keyboard string
KSR

TELEPRINTER/PUNCH
TSF
6041 Skip if teleprinter/punch flag = 1
TCF
6042 Clear teleprinter/punch flag
TPC
6044 Load teleprinter/punch buffer,
Select & print
TLS
6046 Load teleprinter/punch buffer,
Select & print, and clear
Teleprinter/punch flag
SAS
6040 Send a string

2
3
2,3

1
2
3
2,3

HIGH-SPEED READER (TYPE PC02)
6011 Skip if reader.flag = 1
1
RSF
6012 . Read reader buffer & clear flag
2
RRB
6014 Clear flag & buffer & fetch character 3
RCF
RRS
6010 Read reader string
HIGH-SPEED PUNCH (TYPE PC03)
PSF
6021 Skip if punch flag
1
PCF
6022 Clear flag & buffer
PPC
6024 Load buffer & punch character
PLS
6026 Clear flag & buffer, load & punch
PST
6020 Punch string

DECTAPE TRANSPORT (TYPE TU55)
AND CONTROL (TC01)
DTXA
6764 Load status register A
DTSF
6771 Skip on flags
DTRB
6772 Read status register B

9-140

1
2
3
2,3

3
1
2

Table 9-14 (Cont.).

Mnemonic

Code

EduSystem SO Symbol List

Operation

PROGRAM CONTROL
URT
6411 User run time
TOD
6412 Time of day
RCR
6413 Return clock rate
DATE
6414 Date
STM
6415 Quantum synchronization
T5S
6420 Skip on TSS/8
USE
6421 User
SSVV
6430 Set switch register
CKS
6200 Check status
ASD
6440 Assign device
REL
6442 Release device
DUP
6402 Duplex
CON
6422 Console
FILE CONTROL
WHO
6616
SIZE
6614
RFILE
6603
VVFILE
6605
ACT
6617
REN
6600
OPEN
6601
CLOS
6602
PROT
6604
CRF
6610
EXT
6611
RED
6612
FINF
6613

Who
Segment size
Read file
VVrite file
Account number
Rename file
Open file
Close file
Protect file
Create file
Extend file
Reduce file
File information

9-141

Event Time

Table 9-15.

PAL-D Error Diagnostics

Error Code

Explanation

Two PAL-D internal tables have overlapped-This
situation can usually be corrected by decreasing the
level of literal nesting or number of current page
literals used prior to this point on the page.

System device error-An error was detected when
trYing to read or write onto the system device; after
three failures, control is returned to the Monitor.

Systems device full-The capacity of the systems
device has been exceeded; assembly is terminated
and control is returneQ to the Monitor .

.-.~-,-

Illegal character-An illegal character was encountered other than in a comment or TEXT field; the
character is ignored and the"assembly continued.

Illegal redefinition of a symbol-An attempt was
made to give a previously defined symbol a new value
by means other than the equal sign; the symbol. was
not redefined.

Illegal equals-An equal sign was used in the wrong
context.
Examples:
TADA+=B
A+B=C

the expression to the left of (he
equal sign is not a single symbol
or, the expression to the right of
the equal sign was not previously
defined

Illegal indirect-An off-page reference was made; a
link could not be generated because the indirect bit
was already set.

9-142

Table 9-15 (Cont.).
Error CO'de

PAL-D Error Diagnostics
ExplanatiO'n

The prO'gram terminatO'r, $, is missing.

Current nO'nzerO' page exceeded-An attempt was
made to':
a. O'verride a literal with an ins tructiO'n , O'r
b. O'verride an instructiO'n with a literal; this can be
corrected by
( 1) decreasing the number O'f literals O'n the page
O'r
(2) decreasing the number O'f instructiO'ns O'n the
page.

Phase errO'r-P AL-D has received input files in an
incO'rrect O'rder; assembly is terminated and cO'ntrO'I
is returned to' the MO'nitO'r.

SymbO'l table exceeded-Assembly is terminated and
cO'ntrol is returned to' the MO'nitO'r; the symbO'I table
may be expanded to' cO'ntain up to' 1184 user symbO'ls
by saving a file named .SYM O'n the system device.

Undefined symbO'I-A symbO'I has been prO'cessed during pass 2 that was nO't defined befO're the end O'f
pass 1.

Page 0 exceeeded-Same as PE except with reference to' page O.

9-143

9-144

UTILITY PROGRAMS
Symbolic Editor
The EduSystem 50 Symbolic Editor (EDIT) provides the user
with a powerful tool for creating and modifying source files online. Its precise capabilitif;S and commands are detailed in Introduction to Programming 1972, Chapter 5. EDIT allows the user
to delete, insert, change, and append lines of text, and then obtain
a clean listing of the updated file. EDIT also contains commands
for searching the file for a given character.
EDIT considers a file to be divided into logical units, called
pages. A page of text is generally 50-60 lines long, and hence corresponds to a physical page of program listing. A FORTRAN-D
program is generally 1-.3 pages in length; a program prepared for
PAL-D may be several pages in length. EDIT operates on one
page of text at a time, allowing the user to relate his editing to the
physical pages of his listing. EDIT reads a page of t.ext from the
input file into its internal buffer where the page becomes available
for editing. When a page has been compl~tely updated, it is writ~
ten onto the output file and the next page of the input file is made
available. EDIT provides several powerful commands for paging
through the source file quickly and conveniently.
NOTE
The end of a page of text is marked by a
form feed (CTRL/L) character. Form feed
is ignored by all EduSystem 50 language
processors.

To call the Editor, type:
.R EDIT

EDIT responds by requesting INPUT: Type and enter the
name of the source file to be edited. If a new file is to be created
using EDIT, there is no input file. In this case, strike the RETURN
key" EDIT then requests OUTPUT: Type the name of the new,
edited., file to be created. The name of the output file must be
different from the name of the input file. If EDIT is being called
to Ust the input file, there is no need to create an output file; strike
9-145

the RETURN key. When EDIT sets up its internal files and is
ready for a command, it rings the bell on the Teletype.
For example:
.R EDIT
INPUT: WXZOL.D.
OUTPUT:XYZNEft:

(Bell rings at this point.)

Table 9-16.< Symbolic Editor'Operations Summary
Special Characters
Carriage Return
(RETURN Key)

Back Arrow ( ~ )

Rubout (".) .

Function
Text Mode-Enter the line in the
text buffer.
Command Mode-Execute the command.
Text Mode-Delete from right to
of text, continue typing on same
line.
Command Mode-Cancel command. Editor issues a ? and carriage return I line feed.
Text Mode-Delete from right to
left one, character for each rubout·
typed. Does not delete past th~ beginning of the line; Is not in effect
during a READ command.
Command-Mode-'Same as back
arrow;

Form Feed
(CTRL/FORM
Combination)

Text Mode-End of inputs return
to command mode.

Period (.)

Command Mode-Current line
counter used as argument alone or
in combination with + or - and a
number (.,.+5L).

Slash (!)

Command Code-Value equal to
number of last line in buffer. Used
as argument (I-5,LI).

Line Feed (J,)

Text Mode-Used in SEARCH
command to insert a CRI LF combination into the line being
searched.

9-146

Table 9-16 (Cont.).

Symbolic Editor Operations Summary

Special Characters

Function

-----------------------------------------------------Right Angle Bracket (»
Command Mode-List the next
line (equivalent to .+lL).

«)

Left Angle Bracket

Command Mode-List the previous
line (equivalent to . -1 L) .

Equal Sign (=)

Command Mode-Used in conjunction with. and I to obtain their
value (.=27).

Tabulation
( CTRLI TAB Key
Combination)

Text Mode-Produces a tabulation
which, on output, is interpreted as
spaces· if bit 1 of the switch register is set to 0, or as a tab character I rubout combination if bit ]
is set to 1.

--Command
-READ

Table 9-17.

EDIT Command Summary
Meaning

Format
R

Read text from the input file and
append to buffer until a form feed
is encountered.

APPEND

Append incoming text from keyboard to any already in the buffer
until a form feed is encountered.

LIST

List the entire buffer.

List line n.

m,nL

List lines through n inclusive.

Output the contents of the buffer to
the output file, followed by a form
feed.

Output line n, followed by a form
feed.

m,nP

Output lines m through n inclusive
followed by a form feed.

Close out the output file and return
to the Monitor.

PROCEED

TERMINATE

9-147

Table 9-17 (Cont.).
Command
NEXT

EDIT Command Summary
Meanin~

Format
N

Output the entire buffer and a form
feed, kill the buffer and read the
next page.

Repeat the above sequence n times.

KILL

Kill the buffer (i.e., delete all text
lines) .

DELETE

Delete line n of the text.

m,nD

Delete lines m through n inclusive.

Insert before line 1- all the text from
the keyboard until a form feed is
entered.

Insert before line n until a form
feed is entered.

Delete Hne n, replace it with any
number of lines from the keyboard
until a form feed is entered.

m,nC

Delete lines m through n, replace
from keyboard as above until form
feed is entered.

MOVE

m,n$kM

Move lines m through n inclusive
to before line k.

GET

Get and list the next line beginning
with a tag.

Search the entire buffer for the
character specified (but not echoed)
after the carriage return. Allow
modification when found. Editor
outputs a slash (/) before beginning a SEARCH.

Search line n, as above, allow modification.

m,nS

Search lines m through n inclusive,
allow modification.

INSERT

CHANGE

9-148

Table 9-17 (Cont.).
Command

EDIT Command Summary

Format

Meaning

END

Output the contents of the buffer.
Read any pages remaining in the input file, outputting them to the
output file. When everything in tHe
input file has been moved to the
output file, close it out and return
to the Monitor. E is equivalent to a
sufficient number of N's followed
by a T command.

CTRLI C

Stop listing and return to Command
Mode.

Loader
LOADER is used to load programs in BIN format from a disk
file into the user's core area for execution. These files in BIN format can be created by P AL-D in the course of an assembly or they
can be loaded from paper tape using PIP (see the PIP section for
. special instructions on loading BIN format tapes).
To call LOADER, type:
.R. LOADER

LOADER responds by asking for INPUT: Respond by entering
the" name of the file or files to be "loaded. Although many System
Library Programs allow mUltiple input files, the L6ADER uses
this feature to special advantage. Because it loads the files in the
order they are typed, LOADER can be used to load patches and
overlays. After it has requested INPUT, LOADER requests OPTION: For normal operation strike the RETURN key; LOADER
is able to load into any part of core below 7750. If the program
to be loaded is to be debugged, respond to OPTION: with D.
This will cause ODT to be loaded along with the input files and
started. ODT indicates that it is ready by printing a second line
ft!ed. ODT uses locations 7000 through 7577; and if loaded along
with a program which uses any of these locations, the result of the
load is unpredictable.
9-149

EXAMPLE 1: NORMAL OPERATION

.R LOADER
INPUT:MAIN" PATCHl" PATCH2
OPTION:

'BS

EXAMPLE 2: 'LOAD OnT WITH INPUT FILE
.R LOADER
INPUT:PROGl
OPTION: 0

As seen in the first example, LOADER returns control to
Monitor when it is finished. The user can then start the program
by using the Monitor command 'START. For example, LOADER
can be used to load and run the short program given as an example in the section on PAL-D .
• P. LOADER

INPUT: BIN2
OPTION:

'BS
.START 400
0123456789
'BS

NOTE
All BIN format files loaded by LOADER
include a checksum. If LOADER detects a
checksum error while loading, it prints
LOAD ERROR and terminates the load.
Octal Debugging Technique (ODT)
ODT is a powerful octal debugging tool for testing and modifying PDP-8 programs in actual machine language. It allows the
user to control the execution of his program and, where necessary,
make immediate corrections to the program without the. need to
reassemble.

9-150

Th.e .complete command repertoire of ODT is documented in
Introduction to Programming 1972, Chapter 5. ODT (on EduSystem 50) is the high-core version which resides in locations
7000 through 7577. The paper-tape output commands of regular
ODT are not available in EduSystem 50 ODT. To call ODT, the
user types:
.LOAD 2 ODTKI 0 7000
• STAHT 7000

If ODT is to be used to debug a program being loaded with
LOADER, ODT can be loaded and started directly by specifying
the Debug (D) option to LOADER.
ODT executes an SRA (Set Restart Address) as part of its ini.tialization process. As a result, typing CTRL/C always returns
control to ODT. If the program being debugged sets up its own
restart address, typing CTRL/C transfers control to the new
restart address. It is necessary to type tBS followed by START
7000 to force control back to ODT. Every time ODT regains
control, it puts the Teletype in duplex mode. Users debugging
programs which do not operate in duplex mode, should be aware
of this fact.
ODT saves the state of the delimiter mask, when it regains control via a breakpoint. The state of this mask is restored on a
Continue (C) command, but not on a GO (G) command.

Table 9-18.

ODT Command Summary

Command

Meaning

nnnn/

Open register designated by the octal number nnnn.

Reopen latest opened register.

RETURN

Close previously opened register.

LINE FEED

Close register and open the next sequential
one for modification.

UpArrow (t)
( SHIFT / N )

Close register, take contents of that register
as a memory reference and open it.

9-151

Table 9-18 (Cont.).

ODT Command Summary

Command

Meaning

Back Arrow (-E-)
(SHIFT./O)

Close register open indirectly.

Illegal Character

Current line typed by user is ignored, ODT
types ?CRILF.

nnnnG

Transfer program control to location nnnn.

nnnnB

Establish a breakpoint at location nnnn.

Remove the breakpoint.

Open for modification, the register in which
the contents. of AC were stored when the
. breakpoint was encountered.

Proceed from a breakpoint.

nnnnC

Continue from a breakpoint and iterate past
the breakpoint nnnn times before interrupting the user's program at the breakpoint
location.

Open the search mask register, initially set
to 7777. It may be changed by opening the
search mask register and typing the desired
value after the value typed by ODT, then
closing the register.

LINE FEED

Close search mask register and open next
register immediately following,. containing
the location at which the search begins. It
may be changed by typing the lower limit
after the one typed by ODT, then closing
the register.

LINE FEED

Close lower search' register, open next register containing the upper search limit initially set to 7000 or 1000 (location of
ODT). It may be changed by typing the
desired upper limit after the one typed by
ODT and closing the register with a carriage return.

nnnn W

Search the portion of core as defined by the
upper and lower limits for the octal value
nnnn.

9-152

Catalog (CAT)
The Monitor ma;ntains a library of disk files for each user. The
System Library Program CAT is used to obtain a catalog of the
contents of this library. For each file, CAT prints the size of the
file in units of disk segments. The size of a disk segment may vary
among installations. Generally, it is 256 (decimal) words of disk
storage. The protection code for the file is also given. (See the
section on Advanced Monitor Commands for a precise explanation
of protection codes.) If the program was created by any of the
System Library Programs, it has a protection code of 12, meaning that other users can read the file, but only the owner can
change it. To call CAT, type:

.R CAT

The CAT program then prints a listing similar to the one shown
below and concludes by printing tBS and exiting to the Monitor.

.R CAT
DISK FILES FOR USER
SIZE

~AME

FIE

.BI~

PROG • FCL
INTER .BAS
BAS000.TMP
BAS100.TMP
.BAC
INT2
FCLPRG.FCL

TOTAL DISK

1
1
1

1'
2

PROT
17
12
17
17
17

37
12

SEGME~TS:

3,,13

DATE
70
9-JUN-70
9-JUN-70
3-JU~"

9-JU~-70

9-JUN-70
9-JUN-70
9 - JUt\ -70
9

rBS

9-153

9-JU~-70

System Status (SYSTAT)
It is frequently useful to know the status of the system as a
whole; how many users are on-line, where they are, what they
are doing, etc. The SYSTAT program provides this capability.
To call SYSTAT, type:
.SYSTAT

or
.R SYSTAT

SYST AT responds by printing on the first line: 'the version of
the Monitor being run, the time, and the date: SYST AT then reports the uptime which is the length of time in hours, minutes, and
seconds since the system was last put on-line.
SYSTAT then lists all on-line users. Each user is identified by
his account number. The job number assigned to him and the
number of the console he is using are indicated, as is the particular
System Program he is running. The exact running state of each
user, whether he is actually running (RUN), typing (KEY) or
printing (TTY), doing input/output on another system devke
(10 or FIP), or not running (tB), is indicated. The amount of
computer time used by each user since he logged in is given.
If more users are on-line than the system has core fields to
hold them, the fact that the system is swapping is reported. The
number of free core blocks used internally by the Monitor for
Teletype buffering and various other purposes is printed. Then
SYSTAT reports any unavailable devices, i.e., devices which are
assigned to individual users. The job to which they are attached
and their status (AS if they are assigned but not active, AS+INIT
if they are assigned and active) is also indicated. Finally, the
number of available segments of disk storage is reported.

9-154

A sample SYSTAT listing is shown below. SYSTAT terminates
by printing tBS and exiting to the Monitor.

.R SYSTAT
STATUS OF TSS/8.21 DEC PDP-8 II AT 16: 32: 52 ON

2 JUN 70

UPTIME 08:55:52
..JOE,
1
2
3
4

WHO
10 .. 10
3 .. 13
0 .. 10
0 .. 10

AVAILABLE CORE

WHERE

WHAT

STATE

RUNTIME

K00
K15
Kl1
K22

COpy
SYSTAT
BASIC
BASIC

'B
RUN
KEY
KEY

00:00=06
00:00:05
00:00:02
00:00:01

FREE CORE=222

BUSY DEVICES
DEVICE

JOB

1
1
1
3

D2
D3
D6

WHY
AS+INT
AS'+INT
AS
AS
AS+INT

119 FREE DISK SEGMENTS

TSS

•

9-155

9-156

PROGRAMS FOR PAPER TAPE AND DECTAPE CONTROL
PIP (Peripheral Interchange Program)
All System Library programs discussed in previous sections
operate only on files which are on the disk. Disk is a convenient
storage medium for many files; however, it may be more useful to
keep some programs on paper tape. PIP provides a convenient
means of transferring files between disk and paper tape, for those
users who wish to preserve copies of their files off-line.

PIP CONVENTIONS
PIP may be considered a link between disk file storage and
paper-tape devices. To punch a desired file, PIP obtains that file
from the. disk and punches it on paper tape. Similarly, to load a
paper tape, PIP inputs the tape from the reader, then outputs it
to a disk file.
The way files are named is important to PIP. Files on disk are
always named. Paper tapes, on the other hand, have no names as
far as the system is concerned (although the user can label the
physical tape in any manner he chooses). Paper tapes never have
file names; therefore, PIP uses the absence of a file name to indicate a paper tape (absence of a file name is indicated by striking
the RETURN key).
The way in which INPUT: and OUTPUT: is indicated provides
the means for determining the direction of file transfer. If PIP
is to get its input from the disk, the input is a file name; if the
input is from a paper tape, no file name is given. Similarly, if PIP
is to output to the disk, the file name is indicated; if output is to
paper tape, no name is given. To call PIP, type:

.R.PIP

PAPER TAPE TO DISK TRANSFERS
U pdpC:1 ldpt: to OlSK, stnk:e the RETURN key when
PIP requests INPUT: Since PIP must output to the disk, respond
to OUTPUT: by typing a file name. When PIP requests OPTION:
So >oJ

"IVY\,;

9-157

type T to indicate that the paper tape is being loaded from the
Teletype' reader. For example:
.R PIP
INPUT:
OUTPUT: FILEl
OPTION:T

The paper tape in the low-speed reader is read and stored in the
system as FILE t.
DISK TO PAPER TAPE TRANSFERS
To move a disk file onto paper tape, the use of file names is
reversed since PIP must input a disk file and output it to paper
tape. The option remains the same. For example:
.R PIP
INPUT:FILEl
OUTPUT:
OPTION:T

The contents of FILEt are then punched at the Teletype.
HIqH-SPEED READER/PUNCH ASSIGNMENTS
, ' P I P can also be used with high-speed paper-tape devices. The
format of the INPUT: and OUTPUT: responses is the same.
However, for the high-speed reader, the option is R and for the
punch it is P.
Since the reader and punch are assignable devices, they are not
always available (other users may have one or both assigned).
Therefore, Whenever PIP is given a command which utilizes one of
these devices, it checks t6 make sure that the device is available.
If it is, PIP automatically assigns it (thus, it is not necessary to
assign the device before running PIP). If the device is unavailable, PIP informs the user. For example:
INPUT:
OUTPUT: ABeD
OPTION:R

PIP reads the paper tape in the high-speed reader and stores it in
the system as ABCD.

9-158

INPUT:ABCD
OUTPUT:
OPTION:P

PIP punches out file ABCD on the high-speed punch.
INPUT:ABCD
OUTPUT:
OPTION:P
DE:VICE NOT AVAILABLE

The punch is assigned to another user, or there is no punch on the
EduSystem 50, or there is one but it is turned off.
BIN FORMAT FILE TRANSFERS
The examples above work for all ASCII file transfers (except
BASIC programs, explained below.) They are also valid for punching BIN files with either high- or low-speed devices. Loading BIN
format tapes, however, is a special case.
BIN format tapes must end with trailer codes. The easiest way
to ensure that they do is to cut off the tape near the end of the
trailer code. Failure to do this (or cutting it off very unevenly)
does not prevent PIP from loading tape into the disk file. However, later attempts to load the file with LOADER will result in
load errors.
NOTE
Some installations do not allow any BIN
format tapes to be loaded from the lowspeed reader.
lVIOVING DISK FILES
PIP can be used to move the contents of one file into another.
This is often useful in copying a file from another user's library
(providing the file is not protected) into your own library. To
copy from disk file to disk file, specify a file name for both input
and output. Reply to OPTION: by striking the RETURN key.
For example:
I NPUT: F n r: A L ;~
OUTPUT: F()I~{\LX

OPTIO:--J:

PIP gets FOCAL from account number 2's library and moves it
into the file FOCALX.
9-159

DELETING DISK FILES
One of the principal reasons for punching files on paper tape
is to free disk space. Once punched, the disk file is no longer
needed. PIP offers a convenient means of deleting files, the Delete
option:
INPUT:ABCD
OUTPUT:
OPTION:D

PIP deletes file ABCD, provided that the file is not protected
against being changed.
BASIC FILE TRANSFERS
BASIC stores its programs in a unique file format. Therefore,
it is not possible to load 'or punch BASIC files in the usual way.
To provide a convenient means of handling BASIC programs, the
B option is available in ~IP. The B option is used for both reading
and punching BASIC programs. The responses to INPUT: and
OUTPUT: indicate the' direction of the transfer; the high-speed
reader or punch is always assumed for the B option. (To read
or punch tapes at low-speed, use BASIC itself.)
PIP assumes that any BASIC tapes it loads are clean and·errorfree. Only tapes actually created by -BASIC should be loaded with
PIP. Tapes created off-line, and thus liable to contain errors,
should be loaded low-speed by BASIC itself with the TAPE
command.
SAVE FORMAT FILE TRANSFERS
Another special file format is that of the SAVE files, those pro- .
grams directly executed by EduSystem 50. (The System Library
Programs are examples of SAVE format files.) PIP provides the
S option, to allow these files to be punched on paper ~ape. SAVE
format tapes make sense only to PIP. They cannot be input to
/
any other System Program.
The responses to INPUT: and OUTPUT: indicate the direction
of the transfer; the high-speed reader or punch is always assumed
for the S option.
9-160

NOTE
SAVE format tapes include a checksum.
If PIP detects an incorrect read, it prints
LOAD ERROR, and terminates the load,
repeating the request for input.

Table 9-19.

PIP Option Summary

--------------------.....----------------------------------Option
Explanation
-------------------------------------------------------T

Transfer a file between the disk and the Teletype
reader or punch. The response to INPUT: and OUTPUT: indicates the direction of the transfer.

Read a tape from the high-speed reader and store it
as a disk file.

Punch the contents of a disk file on the high-speed
punch.

Delete the file specified for input.

Transfer a BASIC program file between the disk and
the high-speed reader or punch. The response to input and output indicates the direction of the transfer.

Transfer a SAVE format file between the disk and
the high-speed reader or punch. The response to
INPUT: and OUTPUT: indicates the direction of the
transfer.

COpy Program
Many EduSystem 50 installations' include one or more DECtapes. For these installations. DECtape provides a convenient
and inexpensive means of file storage. The COPY program is used
to transfer files between disk and DECtape.
USING AND CALLING COpy
COpy is thc intermediary betwecn disk and DECtape. To write
a disk file out to DECtape. COpy inputs the file from the disk.
then outputs it to the DECtape. To bring a DECtape file onto
the disk, COpy inputs from the DECtape. then outputs to the
disk.
9-161

Files kept on DEC tape have file names just as they do on the
disk. To avoid confusion, the user must tell COpy where the file
is to be found. If it is on DECtape, the DECtape designation and
the number of the DECtape unit must preface the file name. The
DECtape number is always separated from the file name by a
colon. Thus DI :FILEI means the file name FILEI on the DECtape which is currently mounted on DECtape unit number one.
The number of available tape units varies among installations.
The maximum is eight (numbered 0-7). If a file name is not
prefaced by a DECtape number, the file is assumed to be on the
system disk.
Files stored on DECtape do not have protection codes in the
sense that disk files do. They are, however, protected against
unauthorized access. When a DECtape is not mounted, it is not
available to any user. When it is mounted, it is available only to
the user who has assigned the DECtape unit on which it is mounted.
Even then it can not be altered unless the DECtape unit is set to
WRITE ENABLE. Users should be sure to assign a DECtape
unit before mounting their tape, and dismount the tape before
releasing the device. Normally, the DECtape unit to be used
should be assigned before calling COPY.
To call COpy, type:
.R COpy

COPY responds by asking which option the user wishes to employ. The COPY options are discussed below and summarized
in Table 9-20.
LOADING FILES FROM DECTAPE
To load a file onto the disk from DECtape, use the COPY option. When COPY requests OPTION, respond with COpy, or C,
or strike t~e RETURN key (the COPY option is assumed).
When COPY requests INPUT, type the number of the DEC tape .
unit on which the file can be found (DO, DI, D2, D3, D4, D5; D6, .
or D7) followed by a colon and the name of the file on the
DECtape. When' COpy requests OUTPUT, type and enter the
name to be given to the output file on the disk. COPY then
moves the DECtape file onto the disk. '(Wilen using COPY, it is
9-162

not mandatory to insert a space between the device designator
and tht~ device number.) For example:
OPTION- COpy
INPUT - D4:PQR
OUTPUT - PQR

If for any reason, COpy cannot find the DECtape file specified for input (the specified DECtape is unavailable or nonexistent,
or the file name does not exist on that DECtape), COpy prints
a ? and repeats the request for input. If the disk file specified
for output already exists, COPY prints a ? and repeats the request
for output. COPY does not overwrite an existing file. For example:

OPTION - C
INPUT - D9:PQR
?INPUT - D4:PQR~
?INPUT - D4:PQR
OUTPUT - FILEl
?OUTPUT - PQR

SAVING DISK FILES ON DECTAPE
Savjng a disk file on DECtape is very similar to loading one.
The option is still COPY. For input, respond with the name of the
file on the disk. For output, type the DECtape unit number, colon,
and the name to be given to this file. For example:
OPTIO:\l - C
I!'JPUT - ABeD
OUTPUT - D4:ABCD

If Copy cannot find the file on the disk, or if it is protected,
COpy prints a ? and repeats the request for input. If COpy cannot create the desired DECtape file (the specified DECtape does
not exist or is unavaihlble, or it is not WRITE ENABLED, or a
file by that name already exists on the tape) COpy prints a ?
and repeats the request for output.

LISTING DIRECTORIES
COpy can be used to list the directory of a device. To list a
directory, respond to OPTION by typing LIST, or just L. COpy
then asks which device directory it is to list. To list a DECtape
9-163

directory, respond with the device name (DO, ... ,D7). Do not
follow it by a colon. For example:
.R COpy
OPTION- LIST
INPUT- D 1

1372. FREE BLOCKS
NAME
SIZE
BASIC .SAV 66
FACTAL.BAS 10
CONVER. BAC6
PALD .SAV 32

DATE
9-MAR-70
2-MAR-70
1-MAR-70
31-MAR-70

The unit of DECtape storage is the block, which is 128 (decimal) words. Because the unit of disk storage, the segment, is
generally 256 words, a file occupies twice as many blocks of
DECtape storage as· it did segments on the disk.
COpy can also be used to list the user's disk directory. Use the
LIST option, but respond to DEVICE by simply striking the
RETURN key. The directory listing is similar to the listing obtained by running the CAT program.
DELETING FILES
COpy can be used to delete files, either on the disk or on a
selected DECtape. To delete a file, respond to OPTION by typing
DELETE, or just D. Respond to INPUT by typing the name of
the file to be deleted. If the file is on a DECtape, preface the
. file name with the DECtape unit number and a colon. For example:
OPTION - DELETE
INPUT - D4 :ABCD

If COpy cannot find the file to be deleted, or having found it,
cannot delete it (it is a protected disk file or a DECtape file on .
a unit which is not WRITE ENABLED), COPY prints a ? and
repeats the request for INPUT.

DELETING ALL EXISTING FILES ON A DEVICE
COpy can be used to delete all existing files on a device. To do
so, respond to OPTION by typing ZERO, or just Z. When COPY
requests INPUT respond with the name of the device. To delete
all files on the disk, strike the RETURN key. The ZERO option
9-164

should also be used to format a blank DECtape before attempting
to copy any files onto it. For example:
OPTION - ZERO
INPUT - D4
OPTION - Z
INPUT -

COpy cannot delete files from a DECtape unless it is WRITE
ENABLED. -It cannot delete disk files which are write protected.
Table 9-20.

COpy Option Summary

Abbreviation

Explanation

Transfer a file between disk and DECtape.

COpy

List a directory.

DELETE

Delete a file.

ZERO

Delete all files.

Option
LIST

-EXAMPLE OF COPY USAGE
.ASSIG~ D 5
D ·5 ASSIGNED
.R COpy

OPTXON - ZERO
DEVICE - DS
OPTION ~ LIST
DEVICE - DS
1462. FREE BLOCKS
~AME

SIZE

DATE

OPTION - LIST
DEVICE: DISK i~ILES FOR USER 54,40 ON 27-MAY-70.
NAME
SIZE
SOLVE .BAS 1

PROT
12

DATE
27-MAY-70

TOTAL DISK-SEGMENtS: 1

9-165

OPTION - COpy
.INPUT - SOLVE
OUTPUT - DS: SOLVE
OPTION - DELETE
INPUT - SOLVE
OPTION - LIST
DEVICE - D5
1460. FREE BLOCKS

:JAME
SOLVE

SIZE
2

DATE
27-MAY-70

PT IO ~ - LIS T
DEVICE-

DI SI-( FILES FOR USER 5 /l,40

NAME

SIZE

PROT

ON 27-MAY-70'.
DATE

TOTAL DISK SEGMENTS: 0
OPTIO\\:- COpy
INPUT- D5:S0LVE
OUTPUT- ABCD
OPTION- LIST
DEVICEDISK FILES FOR USER 54,40 ON 27 - MAY - 70 •
NAME
ABCD

SIZE
1

PROT
12

DATE
27-MAY-70

TOTAL DISK SEG~ENTS:
OPTION- RENAME
INPUT- ABCD
OUTPUT- FIE.BIN <17>
OPTION- LIST
DEVICE-DISK FILES FOR USER 54,40 ON 27-MAY-70.
NAME
SIZE
FIE • BIN 1

PRO'T
17

DATE
27-MAY-'70

OPTION- 'BS
.RELEASE 0·5

9-166

ADVANCED MONITOR COMMANDS
Introduction
The fundamental Monitor commands described previously are
those needed to utilize existing System Library Programs. The
EduSystem 50 Monitor also provides powerful commands for
~sers who wish to create their own library programs.
To use the System Library Programs described previously, it was
not necessary to be familiar with the actual machine that runs
them, the PDP-8/E. To create new library programs for Edu-'
System 50, this is necessary because they are written in the PDP... 8
assembly language. The user codes his programs for a 4K PDP-8,
subject to the time-sharing conventions discussed in this section.
The programs are created with EDIT, then assembled by PAL-D
and loaded by LOADER. Only at this point are the programs
able to be run by EduSystem 50. In the course of this program
development, the same program exists in many formats.
The source program is a disk file containing ASCII characters
in an Editor format. P AL-D reads the file and translates it into
a second file, the assembled program in BIN format. Neither of
these files is capable of being executed directly by EduSystem 50.
The BIN format tape must be loaded into core by LOADER before it can actually be executed.
At this point it is possible to save the program in a file format
that is directly executable by EduSystem 50. Such a file, caned
a SAVE format file, contains an image of the user's core area
after the program has been loaded by LOADER. These SAVE
format files differ from, all the files which are created by System
Library Programs and cannot be executed directly by EduSystem
50. Thus, it is not possible to save a BASIC program (e.g., FILEt
while running BAS]C), then return to Monitor, type R FILEt,
and get meaningful results. The program in FILEt must be executed under control of the BASIC language processor. Only
SAVE format files can be called into execution directly by the R
command. (All System Library Programs are stored in SAVE
format and can be run with the R command.)

9-167

NOTE
In the following examples, Sn, Cn, and Dn
are used to stand for alphanumeric strings
(such as file names), octal numbers, and
decimal numbers, respectively.
A number of Monitor command conventions are available to
make the commands easier to use. First, more than one command may be typed on a line. Individual commands are separated
by a' semi-colon (;). Second, only enough characters of a command to uniquely specify it need be typed. Thus, DEPOSIT can
be abbreviated DE or DEP .
• LeAD FILEl; DEP

7000; ST 200

is exactly equivalent to:
.LOAD FILEl
.DEPOSIT 20 7000
.START 200

These conventions are available for the elementary Monitor
commands as well. They are, however, especially convenient for
the advanced commands.
Control of User Programs
Once a P AL-D program has been loaded by LOADER, several
Monitor commands are available for controlling its execution.
These commands are shown in Table 9-21.
It is possible to give these utility commands while a user program is running. The CTRL/B character (tB) gets the attention
. of the Monitor without stopping program execution. (tB followed
by the S command stops the program.) tB can be. used together
with the WHERE command to follow program execution. After
executing these commands, Monitor does not put the Teletype
back into Monitor mode.

9-168

Table 9-21.

Monitor Program Control Commands

------------------------------------------------------Command
Explanation
START Cl

Start execution of a user program at
location Cl. When a program is
started, keyboard input is no longer
interpreted as commands to Monitor.
Input characters are passed to the
running program. START Cl c1ears
the user's AC and link.

START

Restart execution of a user program
where it was interrupted (either by execution of an HLT or by tBS typed at
the keyboard) . When the START
command is given, the program's state
is restored.

DEPOSIT Cl C2 ... Cn

Deposit the octal values C2 to Cn in
the locations starting at C 1. DEPOSIT is used to make small octal
modifications to a liser program. No
more than 10 decimal locations can
be modified by a single DEPOSIT
instruction.

EXAMINE Cl

Print the octal contents of location Cl.

EXAMINE Cl D 1

Print the contents of Dl locations
starting at Cl.

WHERE

Print the present status of the user
program. The user's AC, PC, and
LINK are printed. If the processor
includes the extended arithmetic element, two additional registers, the SC
and MQ are printed.

. Defining Disk Files
The Monitor allows the user to save core images of his program on the disk for future use. However, before saving such a
core image, the user must define a disk file in which to save it.
Disk files, like the user's core, are made up of 12-bit words.
Unlike the user's core, which is always 4K in size, a file can be
any s,ize. The unit of disk file storage is the segment; in most installations a segment is 256 (decimal) words but: can be from

9-169

128 to 1024 words long. Files are at least one segment long
when created and g~ow by appending additional segments to the .
end of the file. In defining a file, the user first creates it, then
extends it to whatever length he needs. To have a whole 4K image
ona system with a. segment size of 256 (decimal) words, a 16
segment file is required. If only part of the contents of the user's
core is to be saved, a correspondingly smaller file can be used.
A file can be created at any time. However, to modify or redefine it in any way, the file must be open. Up to four files can be
open for a user simultaneously. Opening a file connects it to an
internal open file number (0, 1, 2, or 3). Once a file is open,
'it is referenced by this internal file number rather than by its file
name.
CREATING A DISK FILE
The CREATE command defines em area of· disk space and
associates it with the name given in the command line.
The file name can be ohe to six alphanumeric characters of
which the first must be a letter .. Creating a file deletes any existing file of the same name, unless that file is write protected. When
created, files are always one segment in size. A new file is arbitrarily assigned a protection code of 12, meaning that other users
may access it but only the owner may change it. Until it bas been
written, the contents of a newly defined file are undefined.
OPENING AND CLOSING A FILE
To use a file, it must first be 9pened with the OPEN command.
A file can be opened on any of four internal file numbers: 0, 1,
2, or 3. A user can have up to four files open at a time. If a file
is open on an internal file number for which a file is already open,
that file is first closed. For example:
.CREATE An
.Op·F:--J 1 AB

AB is now an open file and can be referenced as file 1.
An open file can be closed at any time by means of the CLOSE
command. Once closed, a file cannot be accessed in any way until
it is reopened. It is possible to close more than one file with a
. single command. For example:
9-170

.CLOSE:

1 2

EXTENDING, REDUCING, AND RENAMING
A DISK FILE
'When created, a file is one segment long. If a larger file is
needed, the original file can be extended. For example, the command:
.. EXTENU Cl

extends the file presently open on internal file Cl by Dl segments.
Extending a file adds one or more segments to the end of that file.
The contents of the old part of the file are not changed. Until
written, the contents of the newly added, segments are unspecified.
An existing file may be reduced in size by means of the REDUCE
command. For example, the command:
.. RE:UUCr.: C 1 Dl

reduces the file presently open on internal file Cl by Dl segments. Reducing a file deletes the number of segments indicated
from the end of the file. The contents of remaining segments of
the file are unchanged. If a file is reduced to zero segments, or if
D 1 is greater than the number of segments in the 'file, it is deleted
entirely. An example of the creation and deletion of a 4K file:
• CREATE
• OPEN 3
.' EXTEND
.REDUCE

FOURK
FOUHK
3 15
:3 16

Existing opened files can be renamed. Renaming a file does not
c:hange its contents in any way. For example, the command:
.RENAME,Cl 51

renames as S1 the file open on internal file number C 1.

PROTECTION CODES
The user can protect his files against unauthorized ac£ess. He
.canalso specify the extent of -access certain other users can have
9-171

to his files. For example, a user's associates can be permitted to
look at the data of certain files but not permitted to alter that data.
When it is created, a file is assigned a protection code of 12. This
protection code is defim~d below and can be changed (see Storage
Allocation), but only by the owner of that file. For example, the
command:
.PROTECT Cl C2

gives the protection code C2 to the file open on internal file number Cl.
The protection code is actually a 5-bit mask. Each bit specifies
a unique level of protection. (See the PROTECT lOT command
for the meaning of each bit.)
File protection masks (C2) are assigned as follows:
1

Read protect against users whose project number differs
from owner's.
2 Write protect against users whose project number differs
from ownet;'s.
4 Read protect against users whose project number is same
as owner's.
10 Write protect against users whose project number is same
as owner's.
,20 Write protect against owner. To change the program the
owner must change the protect code.
Protection codes are determined as the unique sum of any of
the above codes. Some of the more common protection codes are
as follows:
Explanation
Command
PROTECT 1 12

Allow other users to access the
file but not change it.

PROTECT'1 17

Allow only the file owner to read
the file. He can also change it.
Allow only the file owner to read
the file. He cannot, however,
change it. (To change it, he
must first change the protection.)

PROTECT 1 37

9-172

Code

Explanation

.PROTECT 1 0

Allow other users to access the
file and change it.

Finally, .. the user can ask what file is open on a given internal
fik number by means of the F (File information) command. For
example, the command:
-,F' C 1

prints the following information about the file presently open on
an internal file C 1 :
a.
b.
c.
d.

Account number of file owner.
Name of file.
Protection code.
Size of file in segments (decimal).

For example:
•F

0010 TYPE 0012

ERROR CONDITIONS
There are a number of error conditions which prevent the ex-.
ecution of the file definition commands (as previously described).
One of the following error messages is printed by Monitor if an
error condition is detected:
Message

Explanation

FILE NOT OPEN

An EXTEND, REDUCE, PROTECT, or RENAME command
has been issued for an internal
file number for which no file is
open.

PROTECTION
VIOLATION

An attempt has been made to
change a file which is write protected against the user.
9-173

Explanation

Message

FILE IN USE

An EXTEND, REDUCE, PROTECT, or RENAME command
has been issued for a file .which
is in use elsewhere by another
user. Because changing a file
which is being used (i.e., has
been opened) could disrupt another user'& work, under these
conditions such a change is prohibited.

DIRECTORY
FULL

A CREATE command· has been
issued, but the user's directory is
full. He can delete any of his
files to make room for the new
file.

FILE NOT
FOUND

the user has attemped to OPEN
a nonexistent file.

FAILEDBYn
SEGMENTS

The user has attempted to extend
a file, but the system has run out
of disk segments. The number
of segments requested, but not
available, is printed.

Saving and Restoring User Programs
Once a file has been defined, the user can save all or any part
of his Jlser core in the file. Files and user core are addressed in
the same way, by 12-bit words. The user can transfer his file into
any part of core.
The SAVE command requires one to five parameters.· The
name of the file to be written into must always be given. If the
file is not in the user's own library, the appropriate account
number is entered before the file name. (Writing into a file owned
by another user is subject to file protection.) In either case, the

9-174

parameters are separated by spaces. The SAVE command writes
the indicated section of core out into the indicated file.
H no parameters follow the file name, Monitor starts at location zero of the user's core and saves it in location zero of the
disk file. It continues to write core locations into the disk file until:
( a) it has written the whole 4 K or (b) it has filled the file. Either
condition completes the SAVE.
The user can further define his SAVE command by indicating
parts of core to be saved in specific parts of the disk file. He does
this by typing one to three parameters following the file name. The
first parameter following the file name indicates a specific disk file
address at which to begin writing. The second parameter following
the file name indicates a specific core address at which to terminate the transfer. If only the first two parameters are typed, the
transfer terminates when either the end of core or the end of file
is reached.
Command

Explanation

SAVE SI
SAVE Cl SI

Assuming that a disk file S 1
exists, and th~tit is not write protected, the contents of core are
saved in S 1. In the first case, S 1 is
assumed to be in the library of the
user giving the command. In the
second case, it is assumed to be in
the library of the user whose account number is Cl.

SAVE Cl C2 C3 C4 Localions C3 to C4 (inclusive)
are saved in file SI starting at disk
file location C2. SI is assumed to
be in the user's own library. If S1
is preceded by the parameter C 1,
it IS assumed to be in the library
of the user whose account number
is Ct.
Once a core image has been saved in a disk file, it can be restored to core by means of the LOAD command. It should be
noted that the Monitor command LOAD is very different from
9-175

the System Library Program LOADER. LOADER loads a BIN
format file (created by PAL-D) into the user's core. LOAD loads
a SAVE format file (created by a previous SAVE command) into core.
The LOAD command requires from one to five parameters. The
name of the- file to be loaded must always be given. If the file is in
the user's own library, this file name is typed after the SAVE
command itself. If it is in another user's library, his account number is entered before the file name. (Reading another user's file
is subject to file protection.) In either case, the parameters are
separated by spaces.
Command

Explanation

LOAD

Read the indicated section of a
disk file into the indicated section'
of core.

LOAD SI
LOAD Cl SI

Assuming that a disk file SI exists,
and that it is not read protected,
_the contents of the file S 1 are
loaded into core. In the first case
S 1 is assumed to be in the library
of the user giving the command.
In the second case, it is assumed
to be in 'the • library of the user
whose accounJ number is D 1.

The user can further define his LOAD command by using the
same optional parameters discussed in the section on the SAVE
command.
Command

Explanation

LOAD SI C2 C3 C4

Locations C3 to C4 (inclusive) are
loaded from file SI starting at file
location C2.

LOAD NEWF 5 10 17

Words 5 to 14 (inclusive) of the file
named NEWF are loaded into locations 10 to 17 of the user's core.
9-176

It is not necessary to open a file before using it in a LOAD or
SAVE command. Both commands automatically open the specified file on internal file number 3 before performing the transfer.
After completion of the command, the file remains open on file
number 3.
A special macro-command, RUN, exists to allow a program to
be loaded and started all in one command.
Command

Explanation

RUNS1
RUN Cl S1

Load file S 1 into core from the
disk and start execution af location O.
In the first example, file S 1 is assumed to be in the user's own
library. In the second, it is assumed to be in the library of the
user whose account number is C1.
RUN S 1 is exactly equivalent to
LOAD S1; START O. RUN Cl
SI is exactly equivalent to LOAD
Cl S1; START O.

The R command (see the section EduSystem 50 Monitor) is a
special case of the RUN command. For example, the command:
.R 51

loads file S1 from the System Library (account number 2) and
starts at location O. R SI is exactly equivalent to RUN 2 S1.
Utility Commands
The Monitor provides a number of special purpose commands
to aid in program development and use. The Monitor utility commands are summarized in Table 9-22.

9-177

Table 9-22.

Monitor Utility Commands

Command

Explanation

USER

Print the number of the job connected with this
user and the console number of the job.

USER Cl

Print the console numbers of job C 1.

SWITCH Cl

Set the user's switch register to Cl. Monitor
maintains a switch register for each user. When
his program executes on OSR (OR the switch
register into the AC) this value is the one which
is loaded.

BREAK

Print the current value of the user's delimiter
mask.

BREAK C]

Set the user's delimiter mask to C 1. (The use
of the delimiter mask is discussed in the chapter
on assembly language programming.

DUPLEX

Place the user's Teletype in duplex mode. All
characters typed at the keyboard are automatically printed as they are entered.

UNDUPLEX

Take the user's Teletype out of duplex mode.
Input characters are received by the Monitor
and by the user program without their being
printed at the console.

RESTART Cl

Set the user program restart address to Cl. If
CTRLI C is typed at the keyboard, Monitor
forces a jump to location Cl in the user's program.

VERSION

Print the version of the Monitor being used.

9-178

WRITING ASSEMBLY LANGUAGE PROGRAMS
Introduction
In addition to tlIe higher-level programming languages available
in the EduSystem 50 library, the user can also code and run programs written in the PDP-8 assembly language, PAL-D (Program
Assembly Language). These programs are prepared with EDIT,
assembled with P AL-D, then loaded with LOADER. For those
users unfamiliar with assembly language programs, Introduction to
Programming 1972 is a useful guide.
A user can program EduSystem 50 just as he would any other
4K PDP-8. (Assembly language programs must fit in 4K of core.)
All memory reference instructions (AND, TAD, ISZ, DCA, JMS,
and JMP) function as on a stand-alone PDP-8. All operate instructions (instruction code 7) also function as on a regular PDP-8
(except that microcoding HL T or OSR with any other operate
instruction but CLA gives unpredictable results).
The major difference between EduSystem 50 programming and
regular PDP-8 programming is in the lOT (input/output transfer)
instructions. Some instructions which are valid on stand-alone
PDP-8s, such as CDF, CIF, ION, IOF are considered illegal instructions under timesharing. There are a great many new lOTs
within EduSystem 50 that are not valid on a regular PDP-8. Finally, there are lOTs which operate on EduSystem 50 in the same
manner as on stand-alone PDP-8s. (Table 9-24 is a summary of
EduSystem 50 lOT Instructions.)
The way EduSystem 50 actually executes an lOT instruction is
also different. Non-lOT instructions (except HLT and OSR) are
executed by the hardware, while lOTs (and HLT and OSR) are
executed. by the EduSystem 50 Monitor.
In general, EduSystem 50 provides the programming capabilities
of a 4K PDP-8 and allows programs of consideral?ly greater complexity to be run within the constraints of each user's 4K of core.
System Library Programs, all of which were written in assembly
language and make use of the EduSystem 50 lOTs dealt with below, are examples of programs which can be run on EduSystem 50.

9-179

Console I/O
User programs handle console (Teletype) I/O in almost the
same way as stand-alone PDP-8 programs. Tlie KRB instruction
is ~sed to input a character, the TLS instruction to output a character. The KSF and TSF (followed by JMP. -1) can be used but
are not needed. Monitor handles all timing problems whether these
skip lOTs are present or not.
EduSystem 50 differs from the stand-alone PDP-8 in that under
EduSystem 50 the user program interacts with multi-character input and output buffers (maintained by Monitor) rather than with
single character registers. Depending on the state of the system,
these buffers may have one, many, or no characters in them. During
normal program execution, this fact is of no consequence. User
programs still send and receive characters one at a time. There are
times, however, when it is useful to clear out any and all characters
in the buffers; a special lOT exists for this purpose (SBC).
On a stand-alone system, characters are input as soon as they
are typed, whether they are of immediate interest or not. Usually,
these characters are stored by the program until a terminating (or
delimiting) character is found. At this time, the whole line of characters is processed. On a swapping, time-sharing. system such as
EduSystem 50, this mode of operation is wasteful. It is far more
efficient to allow input characters to accumulate in the Monitor
input buffer until a delimiter is fouOd. There is an lOt to specify
which characters are to be considered delimiters (KSB).
EduSystem 50 also allows programs to input and output strings
of characters. The read string (KSR) and send string (SAS) instructions provide a convenient and efficient means of doing lengthy
transfers.
All keyboard input uses full-duplexed hardware; there is no
wired connection between the keyboard and printer (Le., characters
are not printed on the console as typed). Input characters are
echoed to' the console under program control rather than by hardware. Because input characters are allowed to accumulate in buffers
before being pass~d to the user program, it is important to have
Monitor perform the echoing rather than user programs. There is
an lOT (DUP) to .set up this automatic echoing as well as an lOT
(UND) to inhibit echoing for such operations as reading tapes.

9-180

Read Keyboard Buffer (KRB)

Octal Code: 6036

Operation: Read the next input character into bits 4-11 of the AC.
Load Teleprinter Sequence (TLS)

Octal Code: 6046

Operation: The ASCII character in AC bits 4-11 is printed on the
user's console.
Skip on Keyboard Flag (KSF)

Octal Code: 6031

Operation: The next instruction is skipped if there is a delimiter
character in the user's input buffer.
Read Keyboard String (KSR)

Octal Code: 6030

Operation: Execution of this instruction initiates a transfer of one
or more characters from th~ user's keyboard to a designated core
area. Before executing KSR, load the AC with the address of a
two-word block, where:
Word 1:

negative of the number of characters to be transferred.

Word 2:

address of the core area into which characters are to
be placed minus one.

The transfer is terminated when either:
a. the indicated number of characters have been input or
b. a dclimiter is seen. At the end of the transfer, the word count
and core address are updated and the AC is cleared.
Send A String (SAS)

Octal Code: 6040

Operation: Before executing an SAS, load the AC with the address
of a two-word block, where:
Word 1:

contains the negative of the number of characters to
be sent.

Word 2:

contains the address -1 of the first word of the string.

The characters are stored one per word right justified starting at
the address specified by word 2. Upon execution of SAS, the system
takes only as many characters as will fit in the output buffer. It
then makes the appropriate adjustment to word 2 to indicate a new
9-181

starting address and to word 1 to indicate the reduced character
count; it returns to the instruction following the SAS. If the character count is reduced to zero, the instruction following SAS is
skipped. The instruction following the SAS should contain a JMP
.- 2 to continue the block transfer of Teletype characters. The
AC is clearly by SAS.
Set Keyboard Break (KSB)

Octal Code: 6400

Operation: Rather than activate a user's prog~am to receive each
character as it is typed, EduSystem 50 accumulates input characters until a certain character, or characters, is seen. To tell the
Monitor which characters to look for (these characters are referred
to as delimiters), load the AC with a 12-bit mask before executing
a KSB. For each bit in the mask which is set, Monitor considers
the corresponding character or characters to be delimiters.
Bit

o
1
2
3
4
5
6
7
8
9
10
11

Specifies
0 = check rest of mask
1 = any character is break.
301-332 (alIletters)
260..,271 (all numbers)
211
( Horizontal tab)
212-215 (line feed, vertical tab, form feed,
RETURN)
241-273 (! " # $ % &
*+ ,- ./ : ;)
240
(space)
274-300 « = >? @)
333-337 ([ / Jt ~)
377
(RUBOUT)
375
(ALT MODE)
anything not in bits 1-10
I

Duplex (DUP)

(

)

Octal Code: 6402

Operation: DU£> informs Monitor that the user wishes each character typed at the console to be echoed on that console's printer as
it is received by Monitor. The DUP instruction does not affect the
user's registers.
9-182

Octal Code: 6403

Unduplex (UND)

Operation: . UND informs Monitor that the user wishes to suppress
character echoing. This can be done for reasons of privacy or because'a program does its own character echoing. The user's registers
are unaffected by UND.
Set Buffer Control (SBC)

Octal Code: 6401

Operation: SBC permits the user program to clear its Teletype input and/or output buffer. Before executing SBC set bits 0 and 1
of the AC as indicated below:
Bit 0
Bit 1

Clear output buffer.
Clear input buffer.

Files and Disk 1/0
All user programs can gain access to disk storage: The timesharing Monitor maintains a pool of available disk space which is
allo~ated in units referred to as segments. (The size of. a disk segment varies among installations. Segm.ents may be 128, 256, 521,
or 1024 words each.) These segments are used to make up user
files on the disk. Monitor also maintains, for each user, a directory
of all files which he has defined.
The lOTs which allow the user to access the disk are of two
types: those which define files on the disk and those which transfer
data between a defined file and the user's core.

NOTE
CREATE and OPEN require that a user
set up a file name in core. FINF and WHO
return file names to core. Each must be
specified in internal code (excess 40 code)
as shown in Table 9-23. Characters are
packed two to a word.
The first step in defining a file is to create it. Creating a file reserves a single segment of disk storage and associates it with a
name. This file can then be extended to any length desired. Extending a file appends more segments to it. Similarly, a file can be
reduced by any number of segments. Reducing a file removes th.e
9-183

last segment or segments from the file. Reducing a file to zero segments deletes it entirely. Once created, a file can be protected,
thereby restricting access to it. When created, a file can be read by
any user, but only the creator can write in it. This protection can
be reset if desired. Finally, it is possible to rename an existing file.
None of these actions affect the contents of the file-they only
reserve space on the disk Until it has been written in, the actual
content of a file is unspecified. Extending a file does not alter the
content of the file as it previously existed. Once defined, files can
be used to read and write data. Any number of words (1 to 4096)
can be moved from any p'art of the user's core to any part of a file
(subject to file protection). The user program specifies a location
in core and a word count. This indicates how many words are to
be transferred and from (or to) where in core they are to be
moved. Also specified is a disk file address indicating what part of
the file is involved. This address is the address of a word in the
file. Files are addressed in the same manner as core: in 12-bit
words. -Unlike core, however, files can be longer than 4K. To address these files provision is made for a 24-bit disk file address,
containing the high-order and lpw-order file addresses.
File addresses are independent of any consideration of segments.
The file address is meaningfuJ only in defining files. Files can be
read and written across segment boundaries without restriction.
(The user cannot read or write beyond the last segment boundary.)
When it exec'utes a file read or write lOT, the system updates the
core address and word count and places an error code in the error
word (see RFILE) if any error is detected. (The error word must
be cleared before execu'ting the lOT.) At the end of a successful
transfer, the word count is set to zero and the ,core address set to
the last word transferred. If the transfer cannot be completed for
some reason, the word count and core address indicate how much
of the transfer was successful; the error word indicates the cause of
the failure. All file operations except CREATE (and OPEN) require that the file be open. Up to four files can be open at a time.
The process of opening a file associates it with one of four internal
file numbers '(0, 1,2, or 3). All file lOTs except CREATE and
OPEN, are specified in terms of one of these internal file numbers,
rather than a fiJe name. lOTs operate on the file which is indicated
by that internal file number at the time. It is therefore possible to
9-184

write file handling programs which are independent of the actual
file (s) they operate on. '
File lOTs, that are successfully completed, return with the AC
cleared. If an error was found which prohibited execution of the
lOT, one of the following error codes is returned:
Code

Explanation

4000

There was no file opened on the specified internal file number.

4400

Attempting to redefine a file which is open to
another user.

5000

Attempting to create a tIle for a user whose
directory is full.

6000

File protection violation.

6400

I nvalid file name.

7000

Attempting to open a nonexistent file.

7400

Disk is full.
Octal Code: 6610

Create a File (CRF)

Operation: The user can request the system to create a new file' of
one segment. The user program provides the new name for the file.
Load the AC with the beginning address of a 3-word block, where:
Words 1 through 3:

contain the 6-character name.

If there is some reason why the request cannot be granted, the
system will return a non-zero error code in the AC. The protection
code of a newly created file is 12. '
Octal Code: 661 1

Extend A File (EXT)

Operation: To extend the length of an existing tlle, that file must
be currently open. Load the AC with the beginning address of a
2-word block, where:
Word I:

contains the internal file number of the file to be extended.
9-185

Word 2:

contains the number of segments the system should
append to the file.

If for some reason the request to

exte~d

a file cannot be granted,
the AC will contain 4000, 4400, 6000, or the number of segrrients
it failed to append.

Reduce A File (RED)

Octal Code: 6612

Operation: To reduce the length of an existing file, that file must
be currently open. Load the AC with the beginning address of a
2-word block, where:
Word 1: contains the internal file number of the file to be
reduced.
Word 2:

contains the number of segments to be removed.

This request is granted unless !he file to be reduced is currently
opened to another user or if the file is write protected against the
user.
Octal Code: 6600

Rename A File (REN)

Operation: REN is used to change the name of a ,file. Load the
AC with the address of a 4-word block where:
Word 1:

contains the internal file number associated with
the file whose name is to be· changed.

Words 2-4:

contains the new name. This name
characters packed two in a word.

IS III

6-bit

Octal Code: 6604

Protect A File (PROT)

'. Operation: The owner of a file can protect his file from unauthorized attempts to access it by uSing this instruction. Before. executing
PROT, load theAC with:
Bits 5 and 6

Internal file number ,of the reserved file to be
protecteQ.

Bit 7

Write protect against owner.

Bit 8

Write protect against users whose project number is same as owner's.
9-186

Bit 9

Read protect against users whose project number
is same as owner's.

Bit 10

Write protect against users whose project number differs from owner's.

Bit 11

Read protect against users whose project number
differs from owner's.

A file must be opened before it can be protected. PROT is legal
only when performed by the file owner, i.e., the user who created
the file. All attempts to access the file which violate any of the protection flags are considered illegal. (For further information on
project numbers, see the section on Storage Allocation.)
Octal Code: 6601

Open A File (OPEN)

Operation: OPEN is used to associate a file with an internal file
number, which is necessary because all file operations are in terms
of the internal file numbers. Before executing the OPEN lOT, load
the AC with the beginning address of a 5-word block, where:
Word 1:

contains the internal file number.

Word 2:

contains the account number of the owner of the
file. If 0, the account number of the current user
is specified.

Word 3-5:

contain the name of the file to be opened. This
name is in 6-bit characters packed two to a word.

If there was another file associated with the internal file number
before the execution of the OPEN lOT, it is closed automatically
before the new file is associated with the internal file number.

Octal Code: 6602

Close A File (CLOS)

Operation: CLOS terminates the association between files and their
internal file numbers. Before executing ci..os, load the AC with a
selection pattern for the internal file numbers whose associated
files are to be closed. The file is closed if bit I is 1, where I = bit 0,
1, 2, or 3.
9-187

READ File (RFILE) and Write File (WFILE)

Octal Code:
6603 & 6605
Operation: Once the association of a file with an internal file number has been made, these lOTs allow the actual file reference to be
made. They are illegal on a file that has not been opened (associated with ail internal file number).
To read or write a file, load the .AC with the address of a6-word
block, then execute the lOT. The format for the 6-word block is:
Word 1:

contains the high-order file word address.

Word 2:

contains the internal file number.

Word 3:

contains the negative of the number of words for the
operation. This number is either the number of
words to be read or the number of words to be
written.

Word 4:

contains a pointer to the beginning address -1 of a
buffer located in the user program. On a read operation this buffer receives the information from the
file: on a write operation this buffer holds the information that is to be sent to the file;

Word 5:

contains the least significant 12 bits of the initial file
word address to begin the operation.

Word 6:

contains an error code:
o if no error
1 if parity error
2 if file shorter than word count
3 if file not open
4 if protection violated

The read or write .begins at the word specified by. words 1 and 5.
For example:
TAD

WFILE

x.,

.+1
(II

-200
6477
200

9-188

means: write 200 (octal) words starting at word 200 of the file
that is associated with internal file number one from a core area
starting at location 6500.
After completion of the transfer, the word count (word 3) and
core address (word 4) are updated. If an error was detected the
appropriate error code is placed in word 6.
File Information (FINF)

Octal Code: 6613

Operation: FINF enables a user program to determine what file,
if any, is associated with an internal file number. Load the AC with
the beginning address of a 7-word block, where:
Word 1:

contains the internal file number for which the
user program wishes information.

Words 2
through 7:

contain the information that the system returns
after executing FINF.

Word 2:

contains the account number of the owner or zero
if no file is associated with the internal file number,
that is, the file is not open.

Words 3-5: contains the name of the file in 6-bit code.
Word 6:

contains:
Bit 1

Word 7:

Means

write protected against owner

write protected against users whose
project number is same as owner's

read protected against users whose
project number is same as owner's

write protected against users whose
project number differs from owner's

read protected against users. whose
project number differs from owner's

contains the number of segments which compose
the file.
9-189

Assignable Devices
. Users can access bqth their own Teletype and the disk; with the
remaining system devices (referred to _as the assignable devices)
this is not true. One function of the Monitor is to ensure that device usage never conflicts. Only one user at a time can access the
high-speed paper-tape reader or punch, or anyone of the DECtapes. To ensure that only one user can access a device, EduSystem
50 requires that the device be assigned before it is used. After a
device is assigned, it is not available until it is released by its owner.
Once assigned, the device is programmed exactly as on a standalone PDP-8. The RRB instruction is used to read a character from
the high-speed reader; the PLS instruction is used to punch one on
the high . . speed punch. The skip lOTs (RFS and PSF) can be used
(followed by JMP .-1) but are not necessary. For block transfers,
there are two string transfer commands: RRS and PST.
The DEC tape instructions have been simplified. A single instruction, DTXA, initiates the transfer of a block of data. The DTRB
instruction is then used to determine if the transfer was successful.
The skip instruction, DTSF, can be used (followed by JMP .-1)
but is not necessary.
Executing any of the assignable device lOTs without first assigning the device gives the following results: (a) If the device is
assigned to another user, the instruction is considered illegal; program execution is now terminated and an error message printed;
(b) If the device is available it is automatically assigned before
execution of the lOT. Th(~ device then belongs to this user until he
releases it.
Because these devices are shared by all users, the Monitor must
ensure that they are operable at all times. In particular, the Monitor
must ensure that a user is not waiting for a device which is not
available. This situation can arise when trying to use the punch
when it is turned off, or when the reader has read off the end of a
tape. All these conditions, known as "hung devices" are considered
to be system errors. If the program doing the transfer has been enabled for system errors (by executing an SEA), control transfers
to the error routine indicated which must clear the error flag in the
status word before continuing (See Program and System Status).
If the user program has not been enabled for system errors, a hung
device causes the program to be terminated and an error message
is printed.
9-190

Octal Code: 6440

Assign Device (ASD)

Operation: If the device specified by the content of the AC is
available, it is. assigned to the user program and the AC is cleared.
Otherwise, the number of the job owning the device is placed in
the AC. If the device does not exist, 7777 is returned in the AC.
4000
4001
4005

Paper-tape reader
Paper-tape punch
DECtape unit N

The assignment is in effect until a corresponding REL instruction
or LOGOUT.
Octal Code: 6442

Release Device (REL)

Operation: The device specified by the contents of the AC is released (providing it was owned by the user executing the REL).
The AC is cleared. Releasing a device makes it available to other
users.
Skip on Reader Flag (RSF)

Octal Code: 6011

Event Time: 1
Operation: The reader flag is sensed, and if it contains a binary 1,
the contents of the PC are incremented by one so that the next .sequential instruction is skipped. The reader flag is bit 8 of status .
register 1, and has a value of 1 if the reader buffer is not empty.
Read Reader Buffer (RRB)

Octal Codes: 6012 &
6016

Event Time: 2
Operation: The contents of the reader buffer are transferred into
bits 4 through 11 of the AC and the reader flag is cleared if the
reader buffer is empty. This instruction does not clear the AC. If
the reader buffer is empty, the user program is dismissed until the
reader flag is 1 or an end-of-tape condition is detected.
9-191

Table 9·23.

Character
Space
!

$
%
&
(
)

+
I
0
1
2
3
4
5
6
7'
8
9

<
>

EduSystem 50 Internal Character Set

6-Bit14
Octal

8-Bit
Octal

06
01
02
03
04
05
06
07
10

240
241
242
243
244
245
246
247
250
251
252
253
254
255
256
257
260
261
262
263
264
265
266
267
270
271
272
273
274
275
276
277

12
13
14
15
16
17
20
21
22
23
24
25
26
27
30
31
32
33'
34
35
36
37

Character
@

B
C
D
E
F
G
H
I

J
K
L

M
N

0
P

Q
R
S
T
U

V
W
X

Y
Z
[

]

6-Bit 14
Octal
40
41
42
43
44
45
46
47
50
51
52
53
54
55
56
57
60
61
62
63
64
65
66
67
70
71
72
73
74
75
76
77

8-Bit
Octal
300
301
302
303
304
305
306
' 307
310
311
312
313
314
315
316
317
320
321
322
323
324
325
326
327
330
331
332
333
334
335
336
337

The 6-bit octal code is used to store passwords and file names only_

9-192

Reader Fetch Charact.er (RFC)

Octal Code: 6014 .

Event Time: 3
Operation: The reader flag and the Monitor reader buffer are both
cleared, the reader is started to fill the Monitor reader buffer and
the reader flag is set after the buffer is full or the end of tape is
detected.
Read Reader String (RRS)

Octal Code: 601.0

Operation: This instruction initiates a transfer from the high-spe(!d
reader to a selected area in the user's core. Before executing RRS,
load the AC with the address of a 2-word block, where:
Word 1:

minus the number of characters to be transferred.

Word 2:

the address of the user core area minus one.

The transfer is terminated by either of two conditions: (a) the
word count is zero indicating that the required number of characters have been read or (b) the reader has read off the end of the
tape (a system error condition). In either case, the word count and
core address are updated. RRS clears the AC.
Load Punch Buffer Se:quence (PLS)

Octal Code: 6026

Operation: The ASCII character is in AC bits 4 through 11 and
is transmitted to the high-speed punch. PLS does not clear the
accumulator.
Skip on Punch Flag (PSF)

Octal Code: 6021

Event Time: 1
Operation: The punch flag is sensed, and if it contains a binary 1,
the contents of the PC is incremented by one so that the next sequential instruction is skipped. The punch flag is bit 9 of status
register 1, and has a value of 1 if the punch buffer is not full. If
the punch flag is 0, the program is dismissed until the punch flag
is 1.
~9-193

Octal Code ': 6020

Punch String (PST)'

Operation: PST allows a user program to punch a string of characters. Before executing PST, load the AC with the beginning address of a 2-word block, where:
Word 1:

contains the negative of the number of characters to
be punched.

Word 2:

contains the beginning address -1 of the string to be
punched; the characters should be right justified one
per word.

After execution of PST, the system takes only as many characters
as fit in the punch buffer; it then makes the appropriate adjustment
to word 2 to indicate a new starting address and to word 1 to .indicate the reduced character count. It returns to the instruction
following the PST which should be a JMP .- 2 to continue the
transfer. If the character count is reduced to zero, the instruction
following PST is skipped. The AC is cleared by PST.
Load Status Register A (DTXA)

Octal Code: 6764

Operation: DTXA allows a user program to read and write records
( 129-wordblocks) on DECtape. Load the AC with the beginning
address of a 3-word block, where:
Word 1:

contains:
Bit 1

Means

0-2

contains the transport unit select number,

3-5

6-8

9-11

for read data function,

for write data function,

Word 2: '. contains the DECtape blo'ck number.
Word 3:

contains the beginning core address -1 of record
buffer.
9-194

After DTXA is given, the DECtape request is placed in the DECtape request queue. After the completion of any DECtape request,
the DECtape flag in status register 2 is turned on. DTXA does not
update word 3. The AC is cleared by DTXA.
Skip on Flags

(D~SF)

Octal Code: 6771

Operation: The content of both the error flag and the DECtape
flag is sampled, and if either flag contains a binary 1, the content
of the PC is incremented by one to skip the next sequential instruction. If both flags are zero, the user program is dismissed until the
skip is satisfied.
Read Status Register B (DTRB)

Octal Code: 6772

Operation: The content of DECtape status register B is loaded
into the AC by an OR transfer. The AC bit assignments are:
Bit

Assignment

error flag
mark track error
end of tape
select error
parity error
timing error
unused
DECtape flag

1
2
3
4
5
6-10
11

Program Control
There are a number of ways thatthe status of a running program
can be changed. The program can be terminated in one of three
ways: by execution of a HLT, by the user typing tBS to force a
program halt, or by a program error which forces Monitor to terminate the program after printing an error message.
It is also possible for the status of a running program to change
without it being terminated. First, the user program can request
that it handle its own program error conditions. In this case, Monitor does not terminate a job on an error; instead, it transfers control to a user error handler. This error handler then determines
what the error was, by a CKS instruction and takes appropriate
action. Monitor also provides the program with an interrupt key,
tC. If the user types a tC, the Monitor unconditionally transfers
9-195

control to. a restart address. Thus, the user program can handle its
own restarts.
Halt (HLT)

Octal Code: 7402

Operation: This instruction is used to stop the user program and
. return control to Monitor. Executing HLT is equivalent to typing
tBS followed by RETURN.
Set Restart Address (SRA)

Octal Code: 6417

Operation: This instruction allows the user to specify an address
to which control is transferred when an tC is typed on the user's
console. Load the AC with the restart address and execute SRA.
If tC is detected, the program's input and output buffers are
cleared, the AC and Link are cleared and control goes to the restart address.
Set Error Address (SEA)

Octal Code: 6431

Operation: This instruction allows the user to specify an address
to which control is transferred in the event of a system error. Load
the AC with an address before executing SEA. If a system error is
detected, Monitor simulates a JMS to the error address. The program counter is stored in the error address and control transferred
to the error address + 1. AC, Link, and input! output buffers are
not affected. The error code of the system error is in STRO bits
9-11. Bit 10 of STRI is set. The error" routine must read these bits
(by a CKS) to determine the cause of the error, then clear them
by means of a CLS.
The only error code that occurs in the course of normal system
usage is due to a hung device. This error occurs when the user attempts to use a punch not already turned on, access a DECtape
not yet selected, or allows the paper-tape reader to run off the end
of a tape. The error routine must release the device to clear the
error condition. The illegal lOT error probably means that an assignable device lOT was executed without the device first being
assigned. Swap and file errors occur if a hardware error is detected
while Moni~or is swapping user program.s or while reading or
writing file directories. These are system malfunctions from which
there is no recovery.
9-196

Program and System Status
Because EduSystem 50 programs run under control of a timesharing Monitor, it is important for them to determine their status
within the system and the status of the system as a whole. Several
lOTs, listed below, have been defined for this purpose.
Octal Code: 6200

Check Status (CKS)

Monitor maintains for each user a complete set of status information, his program's running status and the state of his input/output
devices. This status information, stored in three words, can be accessed by a running program with the CKS instruction. Before
executing a CKS, load the accumulator (AC) with the address of
a three-word block. Executing CKS stores the three status words
(STRO, STR1, and STR2) in the three-word block and clears the
AC. Information about the status of individual devices can also be
checked by the skip lOTs.
The formats of these registers are:
STRO Bits

o
1
2-4
5

6
7
8
9-11

Run Bit
Error Enable
JSIOT
JSIOTC
JSEXON
Error Code

User program is in the run state
Program handles its own errors
Unused
System use only
System use only
System use only
Unused
System detected error condition
1 Illegal lOT
2 Swap read error
3 Swap write error
5 Disk file error
6 Hung device

STR1 Bits

o
1

2
3
4

Timer
File 0
File 1
File 2
File 3

Time is up
Jnternal file 0 is not busy
Internal file 1 is not busy
Internal file 2 is not busy
Internal file 3 is not busy
9-197

STR1 Bits

5
6
7
8
9
10

Teleprinter
Reader
Punch
Error

Wait

There is a delimiter in the input
buffer
Unused
Output buffer is not full
Character in reader buffer
Punch buffer is not full
System error detected, code in bits 7
through 11 of STRO
Job is not waiting

DECtape
Error
DEC tape

Unused
DECtape transfer requested
DECtape error
DECtape flag

Delimiter

STR2 Bits
0-8
9
10
11

Each user has available to him a 12-bit switch register just as he
does on a stand-alone PDP-8. This switch register can be manipulated by means of the Monitor command SWITCH or under program control.
OR With Switch Register (OSR)

Octal Code: 7404

Operation: The content of the user's switch register is inclusively
ORed into the AC.
Set Switch Register (SSW)

Octal Code: 6430

Operation: The content of the AC is stored in the user's switch
register. The AC is cleared. Assembly language programs run
under control of the Monitor. The following lOTs are defined to
allow a program to determine the status of the system as a whole.
Segment Size (SIZE)

Octal Code: 6614

Operation: The segment is the basic unit ·of on-line file storage.
Different EduSystem 50's have differing segment sizes. SIZE allows
a program to determine the segment size. The segment size 'is returned in the AC.
9-19g

Octal Code: 6406

Segment Count (SEGS)

Operation: The number of available disk segments is returned in
the AC.
Account (ACT)

Octal Code: 6617

Operation: The account number (of the job number given) is re. turned in the AC. If AC is 0, the account number for the current job is returned. If the requested job does not exist, zero is
returned.
Who (WHO)

Octal Code: 66-16

Operation: The account number and password of the current job
are returned to the 3-word block whose address is in the AC and
. the AC is cleared.
User (USE)

Octal Code: 6421

Operation: Return in the AC the number of the current job.
Console (CON)

Octal Code: 6422

Operation: Return in the AC the console unit number assigned to
the job whose numbe! is in the AC, if that console number does
not exist, -1 is returned.
User Run Time (URT)

Octal Code: 6411

Operation: Load the AC with the address of a 3-word block,
where word 1 contains the number of the job for which the run
time is sought. ·The run time is returned in the last two locations
of the block. If job is specified, the run time of the current job
is returned. The AC is cleared.

Time-of-Day (TOD)

Octal Code: 6412

Operation: Returns the value of the System Clock in military
time (using a 24-hour cycle) in the two locations starting at the
location of the addl:ess in the AC. The AC is cleared.
Return Clock Rate (RCR)

Octal Code: 6413

.t.

Operation: The number of clock ticks per second is returned in
the AC.
9-199

Octal Code: 6414
Operation: Returns the date in the AC. The format of this 12-bit
number is:
DATE= ( (YEAR-1964 ) * 12+ (MONTH-I) ) *31 + DAY-l
Skip on EduSystem 50 (TSS)

Octal Code: 6420

Operation: This instruction is used by programs which run under
both EduSystem 50 and on a standard PDP-8. Under EduSystem
50, the instruction following TSS is skipped and the Monitor ver. sion number is returned in the AC.On a standard PDP-8, the
lOT has the effect of an NOP instruction.
Quantum Synchronization (SYN)

Octal Code: 6415

Operation: Upon execution of this instruction, the system dismisses the user program and sets it in the run state so that it will
be run again in turn. Ordinarily, this instruction is used to ensure
a full time quantum to perform some critical operation.
Set Time (STM)

Octal Code: 6416

Operation: The system provides a clock time for each user program. By means of this lOT, the time can be set to "fire" after a
specified number of clock ticks have elapsed. Load the AC with
the time (in seconds) to prime the timer. Upon execution of the
STM instruction, the system sets the time to "fire" in the specified
number of seconds and turns the time bit (bit 0) in status register 1 to 0, clears the AC, and dismisses the job. After the speci~
fled time has elapsed, the system turns bit 0 back to 1, and the
job is restarted.
PDP-8 Compatibility

Programming EduSystem 50 in assembly language is very similar to programming a stand-alone PDP-8. All instructions except
the lOTs 'operate identically in either case. As discussed previously, programming such devices as the Teletype and high-speed
reader/punch for EduSystem 50 is somewhat simpler. EduSystem
50 runs programs which include timing loops:. It also properly
executes the JOTs not mentioned in this manual, e.g., TCF, PCF,
etc. Thus,' programs written for stand~alone PDP-8s with Teletype
9-200

and high-speed reader or punch will run on EduSystem 50, although generally not as efficiently as programs which are written
specifically for EduSystem 50.
The same is not true for disk and DECtape operations because
EduSystem 50 uses a simplified programming structure for these
devices. The actual differences in coding are very small. It is a
simple task to adapt previously written code for EduSystem 50 disk
and DECtape.
There are a few standard changes which users generally make
in adapting PDP-8 code to EduSystem 50. Monitor does the
echoing rather than the user program. The TLS which does the
echo can be deleted and a DUP instruction added somewhere
near the start of the program. Also, for efficiency, the EduSystem
50 delimiter capability can be used. A KSB in the program determines what the delimiters are.
Many PDP-8 programs execute a reader and punch lOT early
in the program, to initialize the device, whether they are actually
to be used or not. If the devices are free, they can be assigned and
thus made unavailable to other users. If they are unavailable, the
program terminates on an illegal lOT. Thus, it is important not to
execute these lOTs randomly. If disk or DECtape is involved, the
actual transfer code must be altered to conform to EduSystem 50.
(The fact that core page 37, locations 7600 through 7777, is
available to EduSystem 50 programs is useful in making these
changes. New code can be placed in the area normally reserved
for the Binary Loader.)
The most difficult code to convert is that code which operates
under interrupt. To be run under Edu~ystem 50, these programs
must be recoded so as not to use the interrupt.
lOTs for nonexistent devices are ignored as are CDFs and CIFs
to field zero. (Other CDFs and CIFs are illegal.) It must be remembered that many lOTs have been redefined for use as special
EduSystem 50 instructions. In all other situations, EduSystem 50
remains compatible with stand-alone systems whenever possible.

9-201

Table 9-24.
Number

EduSystem 50 lOT Instruction Summary

Instruction

Program Control
6200
CKS
6402
DUP
6403
UND
6405
CLS
6411
URT
6412
TOD
6413
RCR
6414
DATE
6415
SYN
6416
STM
·6417
SRA
6420
TSS
6421
USE
6422
CON
6430
SSW
6431
SEA
6440
ASD
6442
REL
7402
HLT
7404
OSR

Function

Check Status
Duplex Console
Unduplex Console
Clear Status
User Run Time
Time of Day
Return
, Clock Rate
Date·
Quantum Synchronization
Set Timer
Set Restart Address
Skip on TSS/8
User
Console
Set Switch Register
Set Error Address
Assign Device
Release Device
Halt
OR With Switch Register

File Control

6406
6600
6601
6602
6603
6604
6605
6610
6611
6612
6613
6614
6616
6617

SEGS
REN
OPEN
CLOS
RFILE
PROT
WFILE
CRF
EXT
RED
FINF
SIZE
WHO
ACT

Segment Count
Rename File
Open File
Close File
Read File
Protect File
Write File
Create File
Extend File
Reduce File
File Information
Segment Size
Who
Account Number

9-202

Table 9-24 (Cont.).
Number Instruction

EduSystem 50 lOT Instruction Summary
Function

Input Buffer Control
6030
KSR
6031
KSF
6032
KCC
6034
KRS
6036
KRB
6400
KSB
6401
SBC

Read Keyboard String
Skip On Keyboard Flag
Clear Keyboard Flag
Read Keyboard Buffer Static
Read Keyboard Buffer Dynamic
Set Keyboard Break
Set Buffer Control Flags

Output Buffer Conn"ol
6040
SAS
6041
TSF
6042
TCF
6044
TPC
6046
TLS

Send A String
Skip On Teleprinter Flag
Clear Teleprinter Flag
Load Teleprinter and Print
Load Teleprinter Sequence

High-Speed Paper Tape Reader and Control (Type PC02)
.RRS
Read Reader String
6010
6011
RSF
Skip On Reader Flag
6012
RRB
Read Reader Buffer
6014
RFC
Reader Fetch Character
High-Speed Paper Tape Punch and Control (Type PC03)
6020
PST
Punch String
6021
PSF
Skip On Punch Flag
6022
PCF
Clear Punch Flag
6024PPC
Load Punch Buffer and Punch Character
6026
Load Punch Buffer Sequence
PLS
,

DECtape Control (Type TCOl)
6764
DTXA
Load Status Register A
6771
DTSF
Skip On Flags
DTRB
Read Status Register B
6772

9-203

9-204

STORAGE ALLOCATION
Storage Map
The system's storage allocation is illustrated below.

DISK STORAGE

CSI _r~~J~~~~-~I~;:;B
~-------MONITOR

Figure 9-5.

I fJ

(R~~\- ~::J::1 ~ FI~EJ
fOB

~I..

SWAPPING

AREA-+-FILE AREA------l

EduSystcm 50 Storage Map

File Directories
There are two direCtories on the disk: the Master File Directory
(MFD) referenced mainly by the system, and the User File Directory (UFO), referenced by the user. One of the functions of the
MFD is to service the UFO. A UFO is a particular user's file
directory containing thc names of programs he has created on the
disk.
The UFO is a file like any other file except that its filename is
the project-programmer number and password. When a user is
logged in under a specific number and references the disk, he is
actually referencing his own file area on the disk through the UFD
which has his project-programmer number as its name. He can
specifically code hiS routine to reference UFDs of other users or
the MFO; whether he is successful or not depends on the type
of protection that has been specified for the area he is trying to
reference.

9-205

USER FILE DIRECTORY

MASTER FILE DIRECTORY
WORD 1

PROJECT NO.

IPROG. NO.

(1 CHAR.)

FI LE

(1 CHAR.)

PA SS

(1 CHAR.)

NA ME

(1 CHAR.)

WO RD

(1 CHAR.)

WO RD

(1 CHAR.)

LINK TO NEXT ENTRY

LINK TO NEXT ENTRY
UNUSED

I PROTECTED

BITS

UNUSED

SEGMENT Co,UNT

CONSOLE TIME
CPU TIME
WORD 8

(

PROTECTED _.' BITS

DATE OF CREATION

POINTER TO RETRIEVAL

POINTER

TO RETRIEVAL

LINK TO NEXT RETRIEVAL BLOCK.

0
SEGMENT

SEGMENT

'SEGMENT

SEGMENT

·SEGMENT

SEGMENT .#7

Figure 9-6.

File Directories

Project-Programmer Numbers .
System account numbers are a combination of project number
and programmer number. The account number (always written in
octal) has a binary equivalent. When expressed~s a 12-bit binary
number, the project number is formed by the leftmost 7 bits and
the programmer number is the rightmost 5 bits. For example, the
account number 623 (octal) equals 000 110 010 011 (binary).
The left 7 bits (leading zeros included if any) are 0001100
(binary) and equal 14 (octal) which is the project number. The
programmer number is 10011 (binary) or 23 (octal). Therefore
a user with account number 623 has: project number 14 and programmer number 23.

9-206

a
character codes
ASCII 1 Character Set
8-Bit
Character Octal
A
B
C
D

E
F
G
H
I
J

K
L

M
N

P
Q
R
S
T
U
V
W
X

Y
Z

0
1
2
3
4
5
6
7
8
9

1
2

301
302
303
304
305
306
307
310
311
312
313
314
315
316
317
320
321
322
323
324
325
326
327
330
331
332
260
261
262
263
264
265
266
267
270
271

6-Bit
Octal
01
02
03
04
05
06
07
10
11
12
13
14
1~

16
17
20
21
22
23
24
25
26
27
30
31
32
60
61
62
63
64
65
66
-67
70
71

Decimal
Equivalent
(AI Format)

Character

96
160
224
#
288
$
352
%
416
&
480
544
(
608
)
>I<
672
736
+
800
864
928
992
/
1056
1120
1184
<
1248
l312
>?
1376
1440
@
1504
[
1568
"1632
]
1696
t( 1\)2
,-992
~(_f.l
Leader/Trailer
-928
LINE FEED
-864
-800 Carriage RETURN
SPACE
-736
RUBOUT
-672
Blank
-608
BELL
-544
,-480
TAB
FORM
-416

8-Bit
Octal
241
242
243
244
245
246
247
250
251
252
253
254
255
256
257
272
273
274
275
276
277
300
333
334
335
336
337
200
212
215
240
377
000
207
211
214

Decimal
6-Bit Equivalent
Octal (AI Format)
41
42
43
44
45
46
47
50
51
52
53
54
55
56
57

33
34
35
36
37

-1952
-1888
-1824
-1760
-1696
-1632
-1568
-1504
-1440
-1376
-1312
-1248
-1J84
-1120
-1056
-352
-288
-224
-160
-96
-32
32
1760
1844
1888
1952
2016

-2016

73
74
75
76
77

An abbreviation for American Standard Code for Information Interchange.
The character in parentheses is printed on some Teletypes.

A-I

A-2

a
read ..in mode loadep
The Read-In Mode (RIM) Loader is the first program loaded
into an EduSystem computer.1 This program is loaded by toggling
17 instructions into core memory using the console SWITCH
REGISTER (SR). The RIM Loader instructs the computer to
receive and store, in core, data punched on paper tape in RIM
coded format-primarily the EduSystem system tapes.
There are two RIM Loader programs: one is used when the input is to be from the low-speed (Teletype) paper tape reader; the
other is used when input is to be from the high-speed paper tape
reader. The locations and corresponding instructions for both programs are listed in Table A-I. The procedure for loading (toggling)
the RIM program into core is illustrated in Figure A-I. The RIM
Loader is loaded into field zero of core.
Table A-t.
Location

7756
7757
7760
7761
7762
7763
7764
7765
7766
7767
7770
7771
7772
7773
7774
7775
7776
1

RIM Loader Programs
INSTRUCTION
High-Speed
Low-Speed

6032
6031
5357
6036
7106
7006
7510
5357
7006
6031
5367
6034
7420
3776
3376
5356
0000

6014
6011
5357
6016
7106
7006
7510
5374
7006
6011
5367
6016
7420
3776
3376
5357
0000

The RIM Loader is not needed if the EduSystem has a hardware boot-

strap.

A-I

LOAD RIM

INTO FIELD 0

Figure A-t.

Loading the RIM Loader

After RIM has been loaded, it is good programming practice to
verify that all instructions were stored properly. This can be done
by performing the steps illustrated in Figure A-2, which also shows
how to correct an incorrectly stored instruction.
A-2

When loaded, the RIM Loader occupies absolute locations 7756
through 7776. EduSystems do not use the RIM locations; therefore, RIM need not be reloaded unless the contents of the RIM
locations have been altered by the user.

Figure A-2.

Checking the RIM Loader

A-3

A-4

b
character codes
The ASCIP character codes shown in the following table are
used by EduSystems as the argument in the CHR$ function. For
each ASCII code a second acceptable form is permitted in CHR$.
The second code is obtained by adding 128 to the code given in
the following table. For example, CHR$ would print A in response
to either 65 or 193 as an argument. These codes are also used with
the CHANGE statement in EduSystem 50.

Character
linefeed
form feed
RETURN
space
!

#
$
%
&
(
)

+
J

0
1
2
3
--"> 4,
5
6
7
8
9

<
>
?

ASCII Code No.
. (Decimal)

Character

ASCII Code No.
(Decimal)

12
13
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51

A
B

C
D

E
F
G
H
I

J
K
L
M

(~:-S2>--

53
55
56
57
58
59
60
61
62
63

73
74
75
76
77

N
0
P

78
79
80

R
S
T

82
83
84
85
86
87
88
89
90
91

U
V

64
65
66
67
6R
69
70
71

W
X
y
Z
[

"-]
t

0
0
0
10" *
0
I"" *

""
"
"
"*
61
61
"
0"
"" *
33
33
"
Ii)

33
67

D-18

I""
0
I""
0

*
*

"*
"'"
""'"

"" *
""
""0
"""
"

"
"
33 *

Ii)

33
33
1""

"
"
33
"
""

IIJ

"
"
61
"*
"""
""
"

""
""
""
""
""'"
""
""0
IIJ

"
"'"
""
0

QUESTION
NUMBER
I
2
3
4

5
6

7
8
9
10
I 1
12
13
14
15
16

17
18

19
20
21
22
23
24
25

PAI=tT 2
NO
ANSWER ANSWER ANSWER ANSWER ANSWER
D(~)
EU) RESPONSE
B(X)
C(X)
A(X)
100
0
0
0
0
0
0
0

67
67

0
0
0
0
0

100
33
0
0
0
0
0
0

0
100
33
0
0
0
33

,.:

33
33
0
0
0
33

100
0

,.:

0
0
0
0
0
100
33

0
0

67
0
0

*
*

33
0
0
100
0
0
0
100
0
0
0
100
0
0
0
100
0
0

''""

'0"

0
100

*
*

33
100
0
0

*
*

0
0
0
0
100
0
0
0
0
0

100
0

*
*
*

0
0
0
0
0
)jill 0
0
33
0
0
0

'0"
*

(iJ

0
10'"

*
*

67
0
0
0

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

...................................... ..................
~

D-19

QUESTIONANALYSrS
QUESTION
PART I
I
2

3
4

5
6
7

8
9
1(}J
11
12

13
14

15
16
17
18
19
20
21
22

23
24
25

VALUE
1.75
1.75
3.51
3.51
.R8
1.75
.88
1.75
1.75
.RR
2.63
2.63
.R8
2.63

.RR
1.75
3.51
.88
2.63
1.15
1.75
.88
.88
.88

PART 2

PERCENT
COR'RECT
10'"
1(}J(}J

33.3

IXX

lYtYt
66.7

I
I
IX
I

1 vt~

I(}JYt

33.3

IYtYt
IYHJ
100

33.3
66.7
66.7
66.7
l.YtYt
100
33.3
66.7
1YtYt

1.75

HI(Ij

1.75
1.75
2.63
3.51

lYt0
66.7
66.7
66.7
33.3
10Yt
lVJ0
lVJ0
66.7

1 .75

2.63
2.63

13
14

15
16
17

.88
2.63
2.63
3.51

1 .75

19
20
21

1.75
1.75
1.75
2.63
3.51
1.75
.88

22
23
24
25

IX
IX
I

IXX
IX
I

CORRECT
10VJ

lYt

I
I

10Yt
I(}J(}J

7
R
9

~xx Note the actual decimal
I
value assigned to each
I
response as a result
I
. of Jhe individualized
~ ~x weighting factors.

lItl0

MIS 5 E D

I
I
I
I

1(}J(}J

iV}Cil

3.51
2.63
3.51
1 .75

2
3

TIM E S

100

I
I

IX
IX

66~7

66.7

I
I

IX
IX
IX
IXX
I
I
I

IX
I
I
I

100

lVJYt
10Yt
66.7
lYtYt

This chart gives you
the quickest look at
what the most difficult
questions were.

IX
I
I
1

100

lYt0
33.3

IXX
I
I

1(}J0

..........................................................
D-20

D ISTR 1 BUT ION OF SCORES
RANGE

NUMBER

1~0

I
1
IX
IX
IX
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I

95 TO 99.99
90 TO 94.99
85 TO 89.99
80 TO 84.99
75 TO 79.99
70 TO 74.99
65 TO 69.99
60 TO 64.99
55 TO 59.99
5!i'J TO 54.99
45 TO 49.99
4!i'J TO 44.99
35 TO 39.99
30 TO 34.99
25 TO 29.99
20 TO 24.99
15 TO 19.99
10 TO 14.99
5 TO 9.99
0 TO 4.'99

(if

0
0
0
0
!i'J
!i'J

!i'J
0
!i'J

0
!i'J

0
0

................ ............................ ..... .
~

STATISTICAL MEASURES
•••••••••• THE MEAN (AVERAGE) SCORE IS 86.8419
•••••••••• THE MEDIAN (MIDDLE) SCORE IS 85.965
•• ~ ••••••• THE STANDARD DEVIATION IS 2.58237
••••••••••••••••

• • eo • • • • • • •

e· • • • • • • • • • • • • • • • • •

••••. 9

DO YOU WISH TO SPECIFY GRADES (Y OR N)1Y
A
B
C
D

FOR
FOR
FOR
FOR

GRADE

THOSE SCORES EQUAL ~O OR GREATER THAN195
REMAINING SCORES EQUAL TO OR GREATER THAN?85
REMAINING SCORES EQUAL TO OR GREATER THAN?75
REMAINING SCORES EQUAL TO OR GREATER THAN?!i'l

NUMBER·

IXX

(Ij

D-21

••

DO YOU WISH TO RESPECIFY THE GRADES CY OR N)?Y
A
B
C
D

FOR
FOR
FOR
FOR

THOSE SCORES EQUAL TO OR GREATER THAN?85.965
REMAIN ING SCORES EQUAL TO OR GREATER THAN·? 80
REMAINING SCORES EQUAL TO OR GREATER THAN?60
REMAINI-NG SCORES EQtJAL TO OR GREATER THAN?30

GRADE

NUMBER

IX
IXX

DO YOU WISH TO RESPECIFY THE GRADES (Y OR N)1N
A GRADES ARE:
STUDENT II II
B GRADES ARE:
STUDENT
10
STUDENT
12

*
*

C GRADES ARE:
D GRADES ARE:
F GRADES ARE:

THIS IS THE END OF THE EDUTEST RUN.
THANK YOU.

D-22

EDTEST

The key cards and the student answer cards are imbedded in
EDTEST as a mass of data statements. EDTEST is just the barest
of programs necessary to read and write this data onto the disk
(DECtape) and CHAIN to the next program, EDTST2. This
technique allows EDTST2 to have much more 'working' program
and to pull in data as it is required.
The 4K version of EduSystem-30 allows either 6,000 characters of program and no variables, 600 variables and no program, or some trade-off in between.
This version of EduTest allows you approximately:

2~00 REM ~EnTEST" FlRST PROG~AM IN fOUTEST
2010 REM COP~RIGHT 1972 DIGITAL EQUIPMENT CORPOR~TION
2020 REM MAVNARO, MASSACHUSETTS
203~ REM EOUSVSTEMS 30 AND 40
2040 DIM N(S50)
~0~1 FOR 1-1 TO 5Se\REAO NCI'\IF N(1)-·2 THEN 2042\NEXT I
2~~2 FOR J.l TO I-1\WRITE N(J)\NEXT J
20~3 RESTORE\CHAIN "EOTST2"
20~5 DATA -1,-1,-1,-1,-1,-1,-2
204& END

25 questions x 50+ students
50 questions x 35 students
75 questions x less than 10 students.
The quickest way to significantly expand these limits is to delete
the Unequal Weighting Option of EDTST2 and all handling of
V ( 1) thereafter. If done, 100/ Q is the value of each question.

D-23

EDSTS2

100 ~EM "EDTST2" SECOND PROGRAM IN EOUTEST
110 REM COPYRIGHT 1972 D1GITAL EQUIPMENT CORPORATION
120 REM MAVNARD, MASSACHUSETTS
130 REM EOUSYSTEMS 30 AND·40
1~0 DIM K(50"NC36)i~(S),VC50)
15~ PRINT "HOW MANV QUESTIONS IN THE TEST",
~60 INPUT Q
170 C.INT(CQ-l)/2S1'1
180 FOR l a l 'TO C
190 READ N\IF,Na.9 THEN 200\PRINT "KEY CARD",I,"HAS ,BAD I.D."\STOP
~ 2~0 READ 81,82,a3,B4,BS\NEXT I\RESTORE
N 2;0 FOR 1-1 TO C\READ N
~
220 ~OR J-l TO 5\READ B\GOSU8 1000
230 FOR K.t TO 5\~((I-l)*25+CJ.l)*5+K)aR(K)
2~0 IF (I~1)*25+(J.l)~~+~aQ THEN 210
250 IF R(K)»>al TMEN 260\PRINT"ttAD MARKS ON I-1 THEN 380
3b0 PRINT "NOT ENOUG~ STUDENTS HERE • THERE 'ARE"lI-U"STUDENTS"
370 S-I-l\GO TO 600
,

Q= # students
C=# cards/ student

This set of code
checks the key cards
for hlanksand sets
K (1) to the correct
. key.

s= #

students

Z=# marks counted,
M=# missing marks
end of file?

38~

3q0

4f10

410
420
43~

440

450
4&0
470
480
4q0

t;;
I

V'I

500
510
520
530

540
550

5&121
510
58121
59121

&0121
&10
&20
630

&40

&50
6&0
670
&80

J.l

Read a 5 digit answer
,'OR K-t TO 5
READ 8
block.
GOSUB 1000
NEXT "IF Z>.Q THE'" 560
GOSUB 9&0
This loop is entered
FOR J-i, TO C
only when each student
READ Ni
.
h
d
IFNi aN (I) THEN 500
enteiS mor~ t an 1 car
PRINT "*******.*.STUOENT NUH8ER",N(1)," HAS MISMATCHED 1=0 0 " ,
(>25 questIons).
PRINT" ON CARO",J
This set of code conFOR K_t TO 5
tinues to check for
REAU ~\GOSUB 10~0
missing marks, and
NEXT I(
also matches the I.D.
IF Z>.Q THEN 5b0
numbers of cards 2, 3,
GOSU8 960
etc.
against the stuNEXT J
dent's first card.
NEXT I
READ N
IF N•• l THEN 600
PRINT "TOO ~ANV CARDS FOR",S,"STUDENTS"
PRINT "END OF CARD CHECK • SHALL ~E GO ON (Y OA N)1"r\INPUT SA\PAINT
IF A.jV THEN bia'IF AC>,N THEN 600\STOP
FOR I-t TO 65\PRINT ".",\NEXT I\PRINT
PRINT
PRINT
PRINT\PRINT "ARE THE QUESTIONS EQUALLY WEIGHTED CY OR ~)1"'
This is the code which
INPUT SA\PRINT
allows unequal weightIF Aa,V THEN 840\IF AC>.N THEN 650
ing and generates Vi'
PRINT "ENTER THE WEIGHT FACTOR FOR EACH QUESTION."
the decimal value of

690 fiCA 1-1 TO C'

each question.

7021
7U'I
720
730
740
750
7~0

t:1
I

tv
0\

770
780
790
800
810
820
830
840
850
8621
870
880
8q21
9~11~

910l
92~

930
q40
950
9f,0
971i~

9a0
990

PRINT
PRI ~ T " PAR'T "fI '
FOR Ja1 TO 25
PRI~T "QUESTIUN ."1J,
"

O-eI-1l*25+J

INPUT Yeo)
TaT+V(O)
IF O-Q THEN 8fcl0
NEXT J
NEXT 1
FOR Ial TO Q
V(I)aV(I)*100/T

NEXT I
GO TO 870
FOR 1-=1 TO Q
V(I)a100/Q
NEXT I
PRINT
PRINT
AESTORE\FOA Ia~.C.(S+l)+~ TO 1 STEP -3\FOR J a l TO 1/3
READ 81,B2,B3\NEXT J\WRITE Bl,B2,83\RESTORE\NEXT I\WRITE C,Q,S
FOR 1-1 TO 6*C.CS+l)+b\READ B\NEXT I\~OR 1.1 TO Q\WRITE K(I)\NEXT I
FOR 1.1 TO Q\wRITE VCI)\NEXT I\FOR 1-1 TO S\W~ITE N(I'\NEXT I
PRINT
RESTOHE'
CHAIN "EOTST3"
IF Z+M.25*J THEN q90
PRINT "**********STUOENT NUMBER"IN(I)'" HAS INSUFFICIENT "'
PRINT "MARKS ON CARD",J\MaM+25*J-Z
RETURN

Subroutine to match
total marks against
questions.

1P.100 R(0)a"
1010 FOR X-I TO 5
1020 B.B-R(X-l)*1~·(6-X)
1030 R(Xl-INT(B/1~·(5.X»)
1~4e IF R(X)a0 T~EN 1010
10150 Z.Z.l
1060 NEXT X
1070 RETURN
108~ END

This subroutine takes
the 5 digit answer block
and breaks it into five
separate digits: Rio R 2 ,
R a, R", and R;;.
It also checks for a
zero digit (no mark)
and increments Z for
each good mark,

tj
I

tv
.......:J

Lines 890 and 900 shift the entire data file up 3 spaces, and
insert C, Q and S at the front. Lines 910 and 920 write the ·new
data at the end of the data file.
If Vi routines are deleted to gain space, each routine which
reads the data file must be changed to reflect the absence in
EduTest 2, 3, 4, and 5.

EDTST3·
Hl0

lHl

1?0
130
140

150

lbe
170
1813

O·
I··,

19V1
20~

21 PI

22~
23"

240
2'50
2~0

i70
28Q!
2q~

300
310
3~0

REM "EOTST3" THIRD PHtiGRAM IN EOUlEST
REM·COPYRIGHT 1972 OIGITAL EQuIPMENT CORPORATION
REM MAYNARO, MASSACHUSETTS
REM eOUSVSTEMS 30 AND 40
OIM C(35)r~(5~"R(5),T(35),V(50)
FOR lal TO 65\PRINT ".",\NEXT t\PRINT
REA[lC,Q,S
FOR lal T06*C*(S+1)+b\READ 8\NEXT 1
FOR la1 TO Q\HEAO kC!)\NE~T !\FOR 1-1 TO Q\MEAb V(!)\NEXT I
R£STORE\FOR I~t TO &-C+3\READ 8\NEXT I
PRIN1\P.RtNT
PRINT TA8(20);nSTUOENT RESPONSE MATRIX"
PRINT
PRINT " •••••••••• CORRECT RESPONSES, ARE INDICATED BY -"
PRINT " •••••••••• INCORREC T RESPONSES ARE LISTED"
pAINT ~ •••••••••• A NO-RESPONSE IS INDICATED BY *"
FOR 1-1 TO C
PRINT
PRINT TA8(2b);"PAHT",I
PRINT "STUOENT",TAB(25)'''QUESTION'',TA8C58),"NUMBER",TA8C66),
P~tNT "CUM %"\PRINT "NUMBER"'T'BC2&)'~NUM8ER",TA8(58)'"RIGHT"'
p~rNT TA8C&6)'"GRADE"\PRINT TAB(8),
'OR Jal TO 2S\PkINT CHRSCINTeJ/10)+48)'" ""NEXT J

.
330 PRIN1\PRI~T TAB(8)'
34e, FOR
TO 25\PRINT CHRSCJ-lNTCJ/10)*10+08)," "'\NEXT J

J.,

35'" PRINT
3M') PRINT
370 FOR Jiq TO S

Dummy read to the
teacher's key.

Prints

lf 000
2
1 2 3 ... ·5

38~

C(J):II~

READ N
4~~ PRINT NIT.R(7);
410 FOR 1<=1 TO 5
420 READ,B
430 GOSLJB 7q0
4"~ FOR L=1 TO 5
4S~ O-CI-l1*2S+(K-l)*5+L
3'H'l

4h0

R(L).~(O)

fHEN 490

470 IF'Hella1 THEN 480\PHINT " "'C~RS(RCL)+b3)"GO TO 510
480 PRINT ~ *"'\GO TO 510
49et PRl-NT "
500 C(J)-CeJ)+1\T(J)_T(J)+V(D)
51~ IF OaW THEN 5J0
, 52~ NEXT l'~EXT K
530 FOR MaK+l TO ~\READ 8\NEXT M
~ 5a~ TSINT(T(J)w10+.S)/10

This set of code prints
the student response
matrix.

_'I,

55~ N~INT(lOGCC(J)+.5)/LOG(10))+1\P.INT(LOG(T+,5)/LOG(10')+1

555 IF C(J)c>0 THEN Sb0\NaN+l\p.P+l
Sb0 PRINT TAB(&1-~)'CCJ)'TAB(&8.P)'T
51V1 FOR Ma2 TO C
580 HEAD N,Bl,B2,~3,B4,85
5Q~ IF N<>-l THEN &10
&0~ IF laC THEN 7~0
&10 NEl(l H
,.?~ NEXT J
&30 RESTORE\FOR .pat TO &*C+3\~EAD B\NEXT P
~40 FOR H=1 TO I
&50 READ N,Bl,R2,b3,B4,B5
&&0 NEXT M
&70 PRINT "KEY"JTAB(8)I
&8~ FOR J=l TO 2S\L-CI-l)*2S+J\PRINT CMRS(K(L)+&3)I" ",

How many digits? '
Dummy read to the
next student's card.

Rewind the data file
and get ready for the
next part.

6ge IF LC~ THEN
7~·~ NEXT 1

7~0\NEXT

J\PRINT

7 1 ~., GOT 0 7 '" 0
7?~
75~
7,,~

7~~
7b~

PRINT "KEY"ITABCe)1
FOR J-CI-l'*2~+1 TO Q\PRINT CHRS(K(J'+63)," ",\NEXT J\PRINT
PRINT\PRINT
RESTO~E\FOH 1-1 TO 6*~*(S+1)+2*Q.S+9\REAO 8\NEXT I
FOR I=1 TO S\WRITE TC!)\NEXT I

770 RESTOwe:

7Ae CHAIN "EOTST"'"
7Cjll- R(0)a0
8010 FOR X-I TO 5
R10

8.R~R(X·l)*10-(b·X)

8~0 R(X).INT(~/10-C~-X»)

U
I
!.;J

830 NEXT X
R"'~ RETURN
A5e. END

Note that line 500 calculates each student's score; If deleting.
the Yi routines to gain room, replace the Yen) of line 500 with
100/Q.
~

Dummy read to end
of file.
Write new data.

EDTST4

100
110
120
130
1~0

150
1~0

170
180

9
~

190
200
210
220
230
240
250
2~0

270
280
290
300
310
320
330
3~0

350
360
370

REM "EOTST4" FOURTH PROGRAM IN EOUTEST
REM COPYRIGHT 1972 DIGITAL EQUIPMENT CORPORATION
REM MAYNARD, MASSACHUSETTS
REM EOUSYSTEMS $0 AND 40
D(M K(S0),A(25,6)
FOR 1-1 TO 65\PRINT ".",\NEXT I\PRINT\PRINT\PRINT
READ C,Q,S
FOR 1-1 TO ~*C*(S+1)+~\R!AD B\NEXT I
FOR 1-1 TO Q\READ KCI)\NEXT I\RESTORE
PRINT TA8(i0)1"lTEM ANALYSIS"\PRINT
PRINT " ••••••• , •• NUMBERS SHOWN ARE TO THE NEAREST PERCENT"
PRINT It • • • • • • • • • • CORRECT CHOICES ARE INDICATED BY *"
FOR 1-1 TO C
FOR J-1 TO 25
'ORK-1 TO ~\A(J,K'.0\NEXT ~
NEXT J
PRINT\PRINT\PRINT T_8(26),npART"'I
PRINT "QUE8TION",
FOR J.l TO 5\PRINT TAB(J*7+S)'"ANSW~R"r\NEXT J
PRINT TAB(49)1"NO"
PRINT "NU~BER"JTA8(13)'"A(I)"'TAB(20)'"BCX)"'TABC27),MCCX)"'
PRINT TAB(34)1"O(X)"JTA8(4t)'"£CI)",TA8(G6,,"RESPONSE"
R~STO~E\READ C,Q,S"OR J-1 TO C\REAO N,Bi,Bi,B3,84,85\NEXT J
FOR J.1 'TO I-l\READ N,Bl,B2,83,84,8S\NEXT J
FOR J.l TO S\READ N
FDA Ka1 TO 5
REAO B\GOSUB 640
FOR L-t TO S\X-L+S*CK-1)

Zero the counters.

This set of code counts
the number of times
each part of each
question is chosen.

380
390
400
410
420
430
,,,0
4~0

460
470
480
490

9
~

FOR Ma1 TO 5
IF RCL)c~M+l THEN 400\A(X,M).A(X,M)+1\GO TO 410
NEXT M\A(X,&)aAeX,&)+l
IF 25*CC-l)+X.Q THEN 450
NEXT L
NEXT I(
GO TO "h0
FOR L.K+l TO 5\READ B\NEXT L
FOR La1 TO C-l\REAO N,81,B2,B3,B4,8S\NEXT L
NEXT J
FOR J~l TO 25
)(1I2\PRINT'J;
FOR K.t TO &\Z.INTCA(J,~)/S*100+.5)\GOSUB 590
PRINT TA8((K+l)*1.D)'Z'~IF K.& TMEN Si0\GOSUB &20\NEXT K
IF K(25*(I-l)+J)c2 THEN ~30\PRINT\GO TO 540
PRINT "*"
IF 25*CI-1)+JIIQ THEN 580

500
510
520
5)'"
540
550 NEXT J
5b~ RESTORE\FOR J=l .TO &*C+3\REAO B\NEXT J
570 NEXT,I
580 PRINT\RESTORE\CHAIN "EOTST5 P
5913 .IF ZC~0 TMEN b00\O.1\GO TO 610
6~0 O.INT(LtiG(Z)/LOG(10»+1
610 RETURN
&20 IF XC~K(25*(I-1)+J' THEN &30\PRINT "*"1
&30 X.X+1\RETURN
&40 R(0).0
&50 FOR Vat TO 5

Here these counts
are converted to
percentage points
and printed.

How many digits?
Subroutine.
Is this the correct
answer?
Subroutine.

~~0

8.B.R(V.l)*10-(~.Y)

610 RCV).!NT(B/10~(S.V))
fl80 NEXT Y
6q0 RETURN
7(11121 END

t?
~

The A(25,6) dimensioned in line 140 is used to count the
number of times each of the six possible marks (crossed out, A,
B, C, D, E) is chosen for each of the twenty five questions in
each part of the test. Line 500 is where the complete count is
converted to a percentage point prior to printing.

EDTST5

REM "EnTST~" FIFT~ PROGRAM IN EOUTEST
REM COPV~IG~T 1972 DIGITAL EQUIPMENT CORPORATION
1?0 REM MAYNARD, MASSACIoIUSETTS
13FREM EOUSYSTEMS J0 AND 40
1~r, DIM E(50),F(~~),K(~0),T(35"V(50)
15~ FOR 1-1 to 65\PWINT ".",\NEXT l\PRINT
1 Hl' REA DC, fJ , S
170 FOR 1-1 TO 6*L.(S.1).~\REAO 8\NEXT I
180 FOR 1-1 TO Q\REAO K(I)\NEXT I
190 FOR !-1 TO Q\~EAD VCI)\NEXT I
2~0 FOR 1-1 TO S\k£AO B\NEXT I
21~ FOR 1-1 TO S\~EAD T(I)\NEXT I\RESTORE
2?~ PkINT TAB(23),"QUESTION ANALYSIS"\PRINT
230 PRINT "QUESTIUN"'TAB(13),UVALUEP'TAH(i0,,"PERCENT",
240 PRINT TA8(30);"T I M E S MIS S E 0"
250 FOR 1-1 TO b*C+J\REAn B\NEXT I
2~0 FOR Ial TO S\~OR J-l TO C\REAO N
270 FOR ~.1 TO 5\kEAO 8\GOSUB 700
?be FOR La1 TO 5\U.(J-l)*25+(K-l)*5+L
2q0 IF R(L).K(D) THEN 31~\E(O).E(O)+1
3~e IF O.Q T~EN 3c0
310 .NEXT L\NExT K
32~ FOR M.K+l TQ5\READ 8\NEXT M
33e NEXT J\NEXT 1
3t.1Vi FOR r-l TO C
350 PRINT PPART"'I~TAB(20)'"CORRECT"
lP~
11~

9
~

Count the number of
times each question was
missed. E i·=# misses
on Ith question.

3~e

FOR

J~l

TO 25

371i'1 O-CI-l)*2S+J
360 PRINT J'TA8(lj)'INT((V(O)+.0~5)~1~0)/100'TAB(20)'
390 PRI~T I~T«((S-E(O»/S+.0005)*1000)/10'TA6(30),E(O)'
401i'1 PRI~T 1A8(35)I"I"I
410 IF E(O)a0 THE~ ~50
420

FOR

Kat

430 PRINT
"40 NEX'T

Print question number,
value, percent correct,
times missed, and
bar chart of times
missed.

TO EtO)

11)(11,

45121 PRINT

4&0 IF u-~ THEN
47~ NEXT J

U
I

V-)

49~

'-I 8 V'! NEXT 1
490 PRINT\PIHNT
5~~ FOR 1-1 TO b5\PWINT ".",\NEXT I\PRINT\PRINT
51~ PRINT TAB(21)i"UISTRIHUTION OF SCORES"
52~ FOR Isl TG S

530

J.INT(T(I)+.~05)/5)

'54~

F(J)-F(J)+l

5~0

TaT+T(I)

St-0 NElt'T I
570 PRINT
580 PRINT "HANGE","NUMBER"
5q~ PRINT 1~0,FC2C',"I"'
bli'lli'l FOR 1-1 TO F(20)\PRINT "X"'\N~XT I\PRINT
bl~ FOR 1-95 TO 0 STEP -5
b20 PHINT 1'"TO"ll+LI.9Q,F(I/5),"I"I
b]e FORJ-' TO FCl/5)\PRIhT "X"'\NEXT J\PRINT\NEXT 1
b41i'1 RESTORE\WRITE S,T\FOR t-l TO S\~RITE l(I)\NEXT I
- ...
b~0 FOR 1-1 TO b*C*(S+1)+2*Q+7-S\R~KU e\NtXf 1
b~1i'I FOR 1-1 TO S\~EAO T(I)\NEXT I\RESTORE
b7~ FOR 1=1 TO S+2\REAO 8\NEXT 1
.

Set F(O)=# scores
between 0 and 4.99
F(1) =# scores
between 5 and 9.99,
etc.
T=total of all scores
Print the bar chart
for the distribution
of scores.

680 FOR 1-1 TO S\wRITE TCI)\NEXT I\RESTORE
hQ0 CH.1N

7re

R(0)a0

71~

FOR

"~DTST6"

Y~l

TO 5

720 S-B-R(Y-ll*10-Cb-Y)
73~

7al2l

RCy)apJl(B/10-(S"Yl)
NEXl Y

750 RETURN
END

7H'I

tj
I

EDTST6
/

~EDTST6" $IXTH PROGRAM IN fDUTEST
REM COPYRIGHT 197i DIGITAL EQUIPMENT CORPORATION
REM· MAYNARD, MASSACHUSETTS
REM EDUSYSTEMS J0 AND 40
DIM NC&0),TC&0),Z(&0)
FOR 1-1 TO &5\PRINT "."I\NEXT I\PRINT\PRINT
READ S\READ 1.
FOR 1-1 TO S\kfAD TCI)\NfXT I
FOR Iel TO S\RfAD NCI)\NEXT I

100 REM

110
120
130
140
150
1&0
170
180

190 PRINT

200

PRI~T

2~0

FOR 1-1 TO S\leX)aTCI)\NEXT I

TAB(24),"STATISTICAL MEASURES-

21121 PRINT
2221 MaTIS
230 PRINT " •••••••••• THE MEAN (AVERAGE) SCORE IS",M

This set of code sets
the dummy Zi=Ti .
Sorts the Z! into as_
cending order and
renumbers the sub,
script i accordingly.

250 FOR Ial TO S\FOR JaI TO S
2b~'

IF Z(l)c.ZCJ) THEN 28121

270 O-ZeI)\ZeI)aZlJ)\ZCJ)aO
it80

tJ
I

NEXTJ\NEXT·I

290 IF INTCS/2).S/2 THEN 310 - - - - - - - - - - - - - - - - - ,
300 M2aZ((S-1)/2+1)\GO TO 32121
310 M2·(Z(S/l)+Z(S/i.1»/2
'------ The median score is
32121 ~2aINTe(M2+.0005)*1000)/1000
then the middle Score

330 PRINT " •••••••••• THE MEDIAN

C~IDOLE)

SCORE IS",M2

340 FOR t-l TO S----------------------------------------------,
35121 VaV+CM-TCI"'"'i:!

NEX" I
370 VaV/S

3b0

38121
39121
400
410
42121
43121
u40

450
4&121
w.,~

48121
49121
51210

P~INT

" •••• , •••• ,THE STANDARD DEVIATION IS",SQR(V)
PRINT\PRINT
'.OR 1-1 TO &5
PRINT "."'
NEXT I
PRINT\PAINT\PRINT
PAINT "00 YOU WISH TO SPECIFY GRADES CV OR N)?";
IN"UT SA\PAINT
IF ' •• V TH!N 4~0\IF Ac~'N TMEN 44121
F~INT\FRINt "THIS IS THE END D~THE fOUTEST RUN.~
PRINT "THANK YOU."\STOP
PRINT\PRINT I'A FOR THOSE SCORES EQUAL TO OR GREATER THAN"'
INPUT G(1)\FO~ Gla2 TO 4

if S is odd, or half,
way.between the two
.
mnermost scores If S
is even.

V =variance,
i.e. u:!=~ (u-x):l
x~

Begin letter grading

510 PRINT CMRSCG1+6~),n FOR PEMAINING SCOPES EQUAL TO OR GREATER TMAN"'
520 INPUT G(Gl)\NEXT Gl\LET G(5)-0
530 PRINT\PRINT\FOR 1.1 TO S\FCI).0\NEXT I
Sets F( J ) =# A grades
5"0 FOR 1-1 TO S
F(2) =# B grades
550 FOR (;181 TO 5
5&0 IF T(I)cG(Gl) TMEN 580
etC.
570 F(G1).F(G1)+1\GO TO 590
58~ NEXT Gl
59121 NExT r
M~0 PRINT\PRINT "~RADE",nNUMRE~"\PRINT
Prints bar chart for
6UJ FOR l-l TO 5
,c
~20 Gl-64+1\IF lc~ TMEN 630\G1-70
distribution. of letter
. &30 PRINT"
"'CH~S(Gl)," ",f(I),"I"'
grades.
f,~~ FOR J-t TO F(l)\PRINT "X"I\NEXT J
&50 PRINT\PRINT\NEXT I
o &60 PRINT\PRINT
W ~&7e' PRINT "DO VOU WISH TO RESPECIFY TME GRAOES (Y OR N)?"I
oc .&8121. INPUT 'A\PRINT
&40 IF A•• ' THEN 49121\IF Ac~.N THEN 67121
7~~

PRINT\P~INT

710 FOR Gi:r1 TO '5
72~
73~

7,,0

75C
7&0

770

IF G1<5 THE~ 130\PRINT "F",\GO TO
PRINT CHRSCG1+b~)'
PRINT" GRADES AR~:"
FOR 1:11 TO 5
IF T(I)
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Edu System Handbook Jan73

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