The Rook's Guide To C++ Rooks Isbn Version
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- History
- Variables
- Literals and Constants
- Assignments
- Output
- Input
- Arithmetic
- Comments
- Data Types and Conversion
- Conditionals
- Strings
- Loops
- Arrays
- Blocks, Functions, and Scope
- Problem Solving & Troubleshooting
- The Preprocessor
- Advanced Arithmetic
- File I/O
- Pointers
- Dynamic Data
- Classes and Abstraction
- Separate Compilation
- STL
e Rook’s Guide to C++
26 November 2013
© 2013 Jeremy A. Hansen
All rights reserved.
is work is licensed under a Creative Commons Aribution-NonCommercial-
ShareAlike 3.0 Unported License, as described at
http://creativecommons.org/licenses/by-nc-sa/3.0/legalcode
Printed in the United States of America
First edition: November 2013
ISBN 978-1-304-66105-0
Rook’s Guide Press
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http://rooksguide.org
Preface
What you are reading is the first of what I hope to be many ever-
improving iterations of a useful C++ textbook. We’ve gone fairly
quickly from whim to print on an all-volunteer basis, and as a result,
there are many things that I’d add and change if I had an infinite
amount of time in my schedule. e vast majority of the contents
were wrien in less than 36 hours by 25 students (mostly freshmen!)
at Norwich University over a long weekend. Some of it is mine, and
some was added by our crack team of technical editors as we trans-
lated sleep-deprived poor grammar into sleep-deprived beer gram-
mar.
Where it goes from here is mostly up to you! If there’s a section
that’s missing or in need of clarification, please take a bit of time
and make those changes. If you don’t want to bother yourself with
the GitHub repository, send me your additions and modifications di-
rectly.
I want to first thank my family for the time I didn’t spend with
them on the writing weekend and throughout the summer when I
was editing and typeseing. I promise I won’t do this next summer!
My next thanks go out to the technical editors and typeseers,
without whom you would have a much uglier book. anks to Ted
Rolle for building the initial L
A
T
E
Xframework and to Ma Jadud for
the incredibly helpful pointers on how to manage the pile of typeset-
ting files in a collaborative environment. I also thank Craig Robbins
iii
and Levi Schuck, who, on different sides of the planet, managed to
contribute extensively to the heavy liing of geing the book into
the shape it’s in now. If we ever meet, I owe you a beer or whatever
you’re having!
I also would like to thank all of the Kickstarter backers not only
for the money which made this possible, but for reinforcing the idea
that this is a worthwhile contribution to the community. Peter Stephen-
son and Andrew Pedley also contributed food directly over the text-
book writing hackathon weekend, and without them we’d never have
goen our saturated fat quota! (Note to future project leaders: there’s
nothing that gets a bunch of college students who are generally luke-
warm about programming to write a textbook like free food. It didn’t
even maer what the food was. Really.)
anks to Ma Russo for shooting the video and organizing the
media and social networking efforts with the Kickstarter project through
the writing weekend.
Special thanks to Allyson LeFebvre1for the textbook photogra-
phy, several diagrams, and the extensive search through the semi-
final textbook that turned up a bunch of mistakes that I missed.
And my last (and not at all least) thanks go out to all the stu-
dents who showed up in person or digitally. And without geing
too grandiose, you remind us all that we can make the world beer
by showing up. Keep showing up!
Jeremy
jeremyhansen@acm.org
26 November 2013
1at’s “la-fave”, everyone
Contents
1 History 1
2 Variables 3
2.1 How do I decide which data type I need? . . . . . . . 4
2.2 Identifiers ........................ 4
2.3 Declaring a Variable . . . . . . . . . . . . . . . . . . . 4
2.4 Initializing Variables . . . . . . . . . . . . . . . . . . . 5
2.5 Assignment Statements . . . . . . . . . . . . . . . . . 5
2.6 Review estions . . . . . . . . . . . . . . . . . . . . 6
2.7 ReviewAnswers..................... 6
2.8 FurtherReading ..................... 6
3 Literals and Constants 7
3.1 Literals.......................... 7
3.2 Declared Constants . . . . . . . . . . . . . . . . . . . 7
3.3 Review estions . . . . . . . . . . . . . . . . . . . . 8
3.4 ReviewAnswers..................... 8
4 Assignments 11
4.1 Review estions . . . . . . . . . . . . . . . . . . . . 13
4.2 ReviewAnswers..................... 13
v
5 Output 15
5.1 Review estions . . . . . . . . . . . . . . . . . . . . 18
5.2 ReviewAnswers..................... 19
5.3 Further Reading . . . . . . . . . . . . . . . . . . . . . 19
6 Input 21
6.1 Review estions . . . . . . . . . . . . . . . . . . . . 23
6.2 ReviewAnswers..................... 24
6.3 Further Reading . . . . . . . . . . . . . . . . . . . . . 24
7 Arithmetic 25
7.1 Review estions . . . . . . . . . . . . . . . . . . . . 28
7.2 ReviewAnswers..................... 30
7.3 Further Reading . . . . . . . . . . . . . . . . . . . . . 31
8 Comments 33
8.1 Review estions . . . . . . . . . . . . . . . . . . . . 35
8.2 Review estions . . . . . . . . . . . . . . . . . . . . 37
9 Data Types and Conversion 39
9.1 Floating-point types . . . . . . . . . . . . . . . . . . . 40
9.2 Other types introduced by C++11 . . . . . . . . . . . 42
9.3 Conversion Between Types . . . . . . . . . . . . . . . 42
9.4 Coercion & Casting . . . . . . . . . . . . . . . . . . . 43
9.5 Automatic Types in C++11 . . . . . . . . . . . . . . . 44
9.6 Review estions . . . . . . . . . . . . . . . . . . . . 45
9.7 ReviewAnswers..................... 45
9.8 Further Reading . . . . . . . . . . . . . . . . . . . . . 45
10 Conditionals 47
10.1 if,else, and else if ............... 48
10.1.1 A small digression on expressions . . . . . . . 48
10.1.2 Using else ................... 49
10.2 switch statements .................. 51
10.3 Review estions . . . . . . . . . . . . . . . . . . . . 54
10.4 Review Answers . . . . . . . . . . . . . . . . . . . . . 54
11 Strings 55
11.1 Review estions . . . . . . . . . . . . . . . . . . . . 59
11.2 Review Answers . . . . . . . . . . . . . . . . . . . . . 60
11.3 Further Reading . . . . . . . . . . . . . . . . . . . . . 60
12 Loops 61
12.1 Introduction ....................... 61
12.2 Having Fun while Programming . . . . . . . . . . . 61
12.3 do-while Loops.................... 63
12.4 Event-Based Loops vs Count-Based Loops . . . . . . 65
12.5 for work or for play................. 66
12.6 Picking a Loop . . . . . . . . . . . . . . . . . . . . . . 67
12.7 NestedLoops....................... 68
12.8 Infinite Loops . . . . . . . . . . . . . . . . . . . . . . 68
12.9 Review estions . . . . . . . . . . . . . . . . . . . . 69
12.10 Review Answers . . . . . . . . . . . . . . . . . . . . . 70
12.11 Further Reading . . . . . . . . . . . . . . . . . . . . . 70
13 Arrays 71
13.1 Multi-dimensional Arrays . . . . . . . . . . . . . . . . 73
13.2 Review estions . . . . . . . . . . . . . . . . . . . . 74
13.3 Review Answers . . . . . . . . . . . . . . . . . . . . . 74
13.4 Further Reading . . . . . . . . . . . . . . . . . . . . . 75
14 Blocks, Functions, and Scope 77
14.1 Blocks .......................... 77
14.2 Basic Functions in C++ . . . . . . . . . . . . . . . . . 78
14.2.1 What are functions and why do we use them? 78
14.2.2 e parts of a basic function . . . . . . . . . . 78
14.3 void Functions..................... 81
14.4 Overloading Function Names . . . . . . . . . . . . . . 82
14.5 Scope........................... 83
14.6 Review estions . . . . . . . . . . . . . . . . . . . . 85
14.7 Review Answers . . . . . . . . . . . . . . . . . . . . . 86
14.8 Further Reading . . . . . . . . . . . . . . . . . . . . . 88
15 Problem Solving & Troubleshooting 89
15.1 e Compilation Error . . . . . . . . . . . . . . . . . 89
15.2 eLogicError ..................... 90
15.3 e Infinite Loop . . . . . . . . . . . . . . . . . . . . 90
15.4 Review estions . . . . . . . . . . . . . . . . . . . . 91
15.5 Review Answers . . . . . . . . . . . . . . . . . . . . . 92
16 e Preprocessor 93
16.1 Review estions . . . . . . . . . . . . . . . . . . . . 94
16.2 Review Answers . . . . . . . . . . . . . . . . . . . . . 95
17 Advanced Arithmetic 97
17.1 Examples......................... 98
17.1.1 pow() ..................... 98
17.1.2 sqrt() .................... 99
17.1.3 Modulo ..................... 100
17.2 Review estions . . . . . . . . . . . . . . . . . . . . 101
17.3 Review Answers . . . . . . . . . . . . . . . . . . . . . 101
17.4 Further Reading . . . . . . . . . . . . . . . . . . . . . 102
18 File I/O 103
18.1 I/OStreams........................ 103
18.2 FileI/O.......................... 104
18.3 Opening and closing a File . . . . . . . . . . . . . . . 104
18.4 Reading from a File . . . . . . . . . . . . . . . . . . . 105
18.5 Writing data to a File . . . . . . . . . . . . . . . . . . 106
18.6 Introduction to Classes and Objects . . . . . . . . . . 107
18.7 Other functions . . . . . . . . . . . . . . . . . . . . . 108
18.8 Review estions . . . . . . . . . . . . . . . . . . . . 109
18.9 Review Answers . . . . . . . . . . . . . . . . . . . . . 110
18.10 Further Reading . . . . . . . . . . . . . . . . . . . . . 110
19 Pointers 111
19.1 Review estions . . . . . . . . . . . . . . . . . . . . 114
19.2 Review Answers . . . . . . . . . . . . . . . . . . . . . 115
20 Dynamic Data 117
20.1 Review estions . . . . . . . . . . . . . . . . . . . . 121
20.2 Review Answers . . . . . . . . . . . . . . . . . . . . . 121
20.3 Further Reading . . . . . . . . . . . . . . . . . . . . . 121
21 Classes and Abstraction 123
21.1 structs ........................ 123
21.2 Assigning values to member variables . . . . . . . . . 124
21.3 Classes .......................... 124
21.4 public and private variables and functions . . 125
21.5 Defining member functions . . . . . . . . . . . . . . . 126
21.6 Using member functions . . . . . . . . . . . . . . . . 126
21.7 classes and structs together . . . . . . . . . . . 127
21.8 Constructors . . . . . . . . . . . . . . . . . . . . . . . 128
21.9 Overloading Member Functions . . . . . . . . . . . . 129
21.10 Review estions . . . . . . . . . . . . . . . . . . . . 130
21.11 Review Answers . . . . . . . . . . . . . . . . . . . . . 131
21.12 Further Reading . . . . . . . . . . . . . . . . . . . . . 132
22 Separate Compilation 133
22.1 Review estions . . . . . . . . . . . . . . . . . . . . 135
22.2 Review Answers . . . . . . . . . . . . . . . . . . . . . 136
22.3 Further Reading . . . . . . . . . . . . . . . . . . . . . 136
23 STL 137
23.1 #include <utility>
#include <tuple> (C++11) . . . . . . . . . . . 137
23.2 #include <iterator> . . . . . . . . . . . . . . . . . . . 138
23.2.1 Forward iterators . . . . . . . . . . . . . . . . 139
23.2.2 Bidirectional iterators . . . . . . . . . . . . . 139
23.2.3 Random access iterators . . . . . . . . . . . . 140
23.3 #include <vector> . . . . . . . . . . . . . . . . . . . . 140
23.4 #include <map> . . . . . . . . . . . . . . . . . . . . . 141
23.5 Further Reading . . . . . . . . . . . . . . . . . . . . . 143
Dramatis Personæ
Managing Editor:
Jeremy A. Hansen, PhD, CISSP
Technical Editing & Typesetting:
Jeremy A. Hansen
Ma Jadud, PhD
Craig D. Robbins
eodore M. Rolle, Jr.
Levi Schuck
Media & Outreach:
Mahew E. Russo
Cover Art & Graphic Design:
Allyson E. LeFebvre
Content Authors:
Tyler Atkinson, Troy M. Dundas, Connor J. Fortune, Jeremy A. Hansen, Sco
T. Heimann, Benjamin J. Jones, Michelle Kellerman, Michael E. Kirl, Zachary
LeBlanc, Allyson E. LeFebvre, Gerard O. McEleney, Phung P. Pham, Megan
Rioux, Alex Robinson, Kyle R. Robinson-O’Brien, Jesse A. Rodimon, Mat-
thew E. Russo, Yosary Silvestre, Dale R. Stevens, Ryan S. Sutherland, James
M. Verderico, Christian J. Vergnes, Rebecca Weaver, Richard Z. Wells, and
Branden M. Wilson.
Funding & Support:
Peter Stephenson, PhD, VSM, CISSP, CISM, FICAF, LPI at the Norwich Uni-
versity Center for Advanced Computing & Digital Forensics
Andrew Pedley at Depot Square Pizza
xiii
Kickstarter contributors:
Nathan Adams, Chris Aldrich, Jay Anderson, Kent Archie, Erik Arvedson, Astrolox,
Phoebe Ayers, Papa Joe Barr, Julia Benson-Slaughter, Georgia Perimeter College,
Patrick Berthon, Francis Bolduc, Greg Borenstein, Patrick Breen, Igor Bronshteyn,
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Dave M. Campbell, Brian V. Campbell III, S. Canero, Serge Canizares, Andrew Carl-
berg, Casey B. Cessnun, Winston Chow, W. Jesse Clements, Greg Crawford, Sean
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Chapter 1
History
Developed by Bjarne Stroustrup, C++ has become one of the most popular pro-
gramming languages in the world. Originally, it was designed as an improvement
upon the C language, which was developed by Bell Labs. Developed in the early
1970s, C’s name is derived from the B programming language, which in turn was
derived from the BCPL language. C gained a large following, in part due to its use in
the development of the UNIX operating system. Due to both its popularity and the
number of versions on the market, an American National Standards Institute (ANSI)
commiee was formed in 1982 to create a standard for the C language, which was
adopted in 1989.
Stroustrup began with the idea that object oriented programming would be an
important addition to C, and created C with Classes. In 1983, Stroustrup’s contri-
butions officially became known as C++, its name stemming from C and adding the
++ (increment) operator. It wasn’t until 1998 that the international standard for
C++ was established.
Since then, most changes have been minor. In 2005, a report was released by
the ISO on features that were intended to be included in the next version of C++.
e early versions of this became known as C++0x, until 2011, when the C++11
standard was released by the ISO.
In this book, we’ll favor older techniques, pre-C++11. When C++11 features
are discussed, they will be pointed out as such. While not all of the new features
are discussed, we will be trying our best to explain them as we go.
1
Chapter 2
Variables
Variables are extremely important to every programmer - they will be a critical part
of your programming toolkit regardless of the language you use. Very simply put,
a variable is a space in memory that can store some range of values. Some of the
basic data types are shown in Table 2.1. For a deeper discussion of data types, refer
to Chapter 9.
int Short for integer; stores whole numbers
char Short for character; stores a single leer, digit, or
symbol
bool Short for Boolean; stores true or false
float Short for floating point number; stores numbers
with fractional parts
double Short for double precision floating point num-
ber; stores bigger numbers with bigger fractional
parts than float
Table 2.1: A few basic data types
3
2.1 How do I decide which data type I need?
What you can do with a variable depends on the type of data they contain. For
instance, you can’t store the number 100000 in a char because a char stores
only character data. To store 100000 the programmer should use an int. If you
think you are dealing with numbers that have fractional parts, you need at least a
float. You generally want to use the smallest variable type that will get your job
done. Simply put, if it is a round number, int works fine; if it’s a true or false,
use bool; for a leer, use char; for fractional numbers, use float; for a really
big number or a number with many digits aer the decimal point, use double.
2.2 Identifiers
Now we have an idea of what types of variables we will use in the program. How do
we have the program differentiate between multiple ints, chars, or doubles?
We have to name them! e name we use will give the variable an identity, so it’s
known as an identifier. An identifier can be almost anything you’d like, provided
the identifier does not begin with a number or symbol.1Remember that the variable
name can only be one word long. You may use a an underscore to replace a space
if you so desire, and note that C++ is case sensitive. at is, testresults,
TestResults, and Test_Results are all different identifiers.
2.3 Declaring a Variable
e line of code that creates a variable is called a declaration. A declaration is the
program telling the computer “save a place in memory for me with this name.”
A declaration for an integer variable named myVariable looks like this:
i n t m yVa r ia b le ;
e specific syntax—the set of grammatical rules for the language—is impor-
tant to follow when declaring variables. Notice that the first part (int) is the data
type of the variable. e second part is the identifier (myVariable), or variable
name. e last part is the semicolon (;) which signifies the end of a statement. You
can think of the semicolon in C++ as equivalent to a period at the end of a sentence;
1ere are a few exceptions, including those words that describe data types (as
in the table above) and other keywords such as if and while, which you’ll learn
about in later chapters.
it is the end of a complete thought. Note that you may declare several variables of
the same data type together. Consider this example:
i n t x , y , z ;
double a ;
e above example creates three variables of type int named x,y, and zand
one variable of type double named a.
2.4 Initializing Variables
Values can be immediately assigned to a variable at the time of its declaration. is
is known as initializing a variable. To do this, the variable’s name is followed by
an equals sign (=, the assignment operator), the value, and a semicolon. Consider
this example:
i n t x = 2 0 ;
double a = 2 . 2 ;
Note that uninitialized variables can cause problems if they are used anywhere
before they are assigned a value. When a variable is declared, it contains whatever
was already in that space of memory, which can give them unpredictable values.
is means that is is oen a good idea to initialize variables to some sensible initial
value when they are declared.
2.5 Assignment Statements
An assignment statement is a method of assigning a value to a variable aer it
has been declared. All assignment statements have the variable being assigned the
value on the le side of an equals sign and the value to assign on the right side.
Note that the expression on the right side of the assignment may contain arithmetic
operations such as multiplication, division, addition, and subtraction, or even other
variables. Consider the following example:
i n t a = 1 , b = 2 , x = 0 , y = 0 ;
x = a + b ;
y = x ;
2.6 Review estions
1. Declare two variables of type int and initialize them to an appropriate
value.
2. Declare three integer variables: sum,a,b. Initialize the variables aand b
to an appropriate integer and use an assignment statement to assign sum
the result of aplus b.
3. Declare a double variable called number and initialize it to 13.6.
4. Create a program in which 3 variables are declared. Create one float
named myFloat, one int named myInt, and one double named my-
Double. Initialize them to 3.14,3, and 3.14159, respectively.
2.7 Review Answers
1. int a = 6;
int b = 0;
2. int sum, a = 6, b = 0;
sum = a + b;
3. double number = 13.6;
4.
i n t main ( )
{
f l o a t my F loat = 3 . 1 4 ;
i n t myInt = 3 ;
double myDouble = 3 . 1 4 1 5 9 ;
r e t u r n 0 ;
}
2.8 Further Reading
• http://www.cplusplus.com/doc/tutorial/variables/
• http://www.tutorialspoint.com/cplusplus/cpp_variable_types.htm
Chapter 3
Literals and Constants
3.1 Literals
A literal is a value outside of a variable such as 5,9,103, and −21. Each of those
is an int, but a literal can be of any data type. e point is, these are values that
the C++ compiler already recognizes, and can’t be changed. In other words, you
can’t convince the compiler to give the literal 3 the value of 4, because 3 is constant.
Table 3.1 contains a few examples.
3.2 Declared Constants
We call a variable whose value we cannot change a constant. Aer you declare
a constant, you are unable to change it, no maer what. e difference between
declaring a normal variable and a constant is that we simply place the keyword
const before the data type in the declaration. is indicates whatever variable
and type that follows the const will be a constant and cannot be changed. Since
it is a constant, we will also need to initialize the value at the time we declare the
variable. Here is an example (we cover the cout object shortly in Chapter 5):
c o ns t f l o a t p i = 3 . 1 4 ;
f l o a t r a d i u s = 5 , a r ea ;
a re a = r a d i u s * r a d i u s * p i ;
c o u t << a r e a ; / / o u t p u t s 7 8 . 5
7
Literal value Data Type
123.45f float
13.8903 double
-389283220.342423 double
49e-8 double
12 int
12u unsigned int
'x' char
"text" string
true bool
false bool
Table 3.1: Examples of a few literals
3.3 Review estions
1. Describe the difference between literals and declared constants. When would
a declared constant be more useful than a literal constant?
2. What is the difference between a normal variable and a constant?
3. Build a program in C++ that does the following:
(a) Declare a double variable named Feet. Initialize it to your height.
(b) Declare a double constant named MetersPerFoot, with the
value of 0.3048.
(c) Declare a double variable named Meters. Set it to Feet multi-
plied by MetersPerFoot.
4. Create a program that displays the diameter and area of a circle for any given
radius. Use a const float to represent π.
3.4 Review Answers
1. A literal is a value not stored in a variable; a constant is an unchanging value
stored in a variable.
2. Normal variables can be changed or overwrien; constants cannot be changed
or overwrien.
3.
d o u b l e F e e t 5 . 5 ;
c o n s t d o u b l e MetersPerFoot = .3048;
d o u b l e M e te r s = F e e t * M e t e r s P e r F o o t ;
4.
float r a d i u s = 5 ;
c o n s t f l o a t p i = 3 . 1 4 1 5 9
d o u b l e d i a me t e r , a r e a ;
d i a m e t e r = r a d i u s * 2 ;
a re a = p i * ( r a d i u s * r a d i u s )
Chapter 4
Assignments
Assignments are a way for a user or a programmer to assign a value to a variable.
e way we assign a value to a variable in C++ is different from how we might do
it in math. In mathematics we are allowed to say that x = 3 or 3 = x, but in
C++ the only acceptable way to assign the value of 3to xis to type x=3.
e =in the expression x = 3 is known as an assignment operator. is
allows the program to set a variable’s value depending on its type. Here are some
examples of seing a value to different types of variables:
i n t x = 4 ;
char a l p h a = ’A ’ ;
s t r i n g word = ” Alpha ” ;
f l o a t y = 3 . 1 4 ;
We are able to declare variables and assign a value to those variables immedi-
ately by using the assignment operator. When we assign literal values to variables
of type char, the value must be surrounded by single quotes (for example, 'A').
When we assign values to variables of type string, the literal value must be sur-
rounded by double quotes (for example, "Alpha"). We do not have to initialize
the values of the variables, however. We can set them later in the code like this:
i n t myVal ;
/ / some c o d e
myVal = 0 ;
In all of the lines of code in this section where a variable is set using the as-
signment operator, the “thing that is being given a value” is known as an lvalue,
and the expression on the right that is being stored in the variable is known as the
11
rvalue. Literals such as 'A' or 3can never be an lvalue. Aside from literals, the
rvalue can consist of other variables, like this:
myVal = myVal2 ;
Even though myVal2 is a variable, we are only using the value stored in the
variable, not the variable itself. For example, if myVal2 had a value of 6,myVal
would then be assigned to the value 6with the above code.
We can also store the results of an arithmetic expression in a variable like this:
myVal = 5 + 6 ; / / a s s i g n s myVal a v a l u e o f 1 1
But we can’t write
5 + 6 = myVal ; / / ERROR !
since 5 + 6 doesn’t refer to a place where we can store a value. We can also
combine arithmetic expressions with variables as an rvalue like this:
myVal2 = 6 ;
myVal = 4 + myVal2 ;
In this case, the variable myVal would be assigned a value of 10 because the
variable myVal2 was initialized to a value of 6, and 4+6is 10. e value
of myVal2 remains unchanged. Make sure that the variable myVal, the variable
myVal2, and the literal 4are of the same type. For example, the following code
will result in an error:
i n t myValue = 4 ;
i n t yourVal ;
s t r i n g m y S tri n g = ” word ” ;
you r Val = myValue + my S t ring ;
/ / Adding s t r i n g to an i n t i s
/ / p r o b a b l y n ot what you meant !
When we try to combine different variable types, the compiler will get very
mad at us. Some exceptions to this rule are if we try to combine floats, ints,
and doubles. ese types have the ability to be combined (to a certain extent)
because they are all numeric values. Both doubles and floats can hold values
with a decimal point such as −3.14,0.003, or 5.167289 whereas an int can only
hold round values such as 2,−18, or 100. Refer to Chapter 9 for more information
on converting between data types.
4.1 Review estions
1. Which of the following is an incorrect way to assign a value to a variable x
of type int?
(a) 7 = x;
(b) int x = 7;
(c) int x(7);
(d) x = 7;
2. Which of the following is an incorrect way to assign a value to a variable of
type string?
(a) string myString = "word";
(b) string myString = 'word';
(c) myString = "word";
3. Is the following code incorrect? If so, why? If it is correct, why?
i n t x = 6 , y ;
ch ar myChar = ’ x ’ ;
y = myChar + x ;
4. Write a program that declares two int variables and two double vari-
ables. Add and subtract five from each of your declared integer variables.
en add and subtract 7.32 your double variables by 7.32. en output
each of your results to the screen.
4.2 Review Answers
1. a. When we store a value in a variable, the variable goes on the le of the
assignment operator, and the value being stored in that variable goes to the
right of the assignment operator.
2. b. String literals must be surrounded by double quotes, not single quotes;
single quotes are used for single characters like 'b'.
3. e code is incorrect. is will probably not produce the expected result it
tries to add an int and a char and store that value in a variable of type
int.
Chapter 5
Output
Output in C++ is done with the object cout (“console output”). e object cout
prints useful information to the screen for the user. For example, if we wanted to
prompt the user with
Type in your name:
we would use cout.cout is extremely important when you are starting to learn
C++ as it gives you the ability to display the current state of any variable and provide
user feedback at any point in your program. Let’s make a program that outputs
something to the screen:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
c o u t << ”Go C a d e ts ! ” ;
return 0 ;
}
e symbol << is called the insertion operator and is needed between cout
and what you want to display to the screen. In this case, we are displaying a string
literal "Go Cadets!". As you know, every statement in C++ ends with a semi-
colon, and this one is no exception.
What if we want to print more, though?
15
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
c o u t << ”Go C a d e ts ! ” ;
c o u t << ” You can do i t ! ” ;
r e t u r n 0 ;
}
Try to compile and run that. It works, but it’s not really the desired output.
You should get:
Go Cadets!You can do it!
How do we get those on a different line? One of the ways we can do it is to
use the object endl.endl means “end line”, and is used when you want to end
one line and start over on the next—it’s like hiing enter on your keyboard. You
will also need another redirect operator between the string literal and the endl.
Puing all of this together looks like this:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
c o u t << ”Go C a d e ts ! ” << e n d l ;
c o u t << ” You can do i t ! ” ;
r e t u r n 0 ;
}
is prints:
Go Cadets!
You can do it!
at works a bit more as intended. Alternatively, we can combine the two lines
that use cout into a single one like this:
c o u t << ”Go C a d e ts ! ” << e n d l << ” You can do i t ! ” ;
Another way we can accomplish this, without needing another redirect oper-
ator, is with the special character '\n'.'\n' is a newline character, it prints a
new line just like the endl object.
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
c o u t << ”Go C a d e ts ! \ nYou can do i t ! ” ;
return 0 ;
}
is prints:
Go Cadets!
You can do it!
Another thing we can use with the console output object is the special character
'\t'. Printing this character is the same as pressing the tab key on your keyboard,
and is used for indentation and formaing. Let’s look at an example that uses the
newline character, the tab character, and some text:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
c o u t << ” \ tGo Ca d et s ! \ nYou can do i t ! ” ;
return 0 ;
}
is code prints:
Go Cadets!
You can do it!
We don’t always have to output words the screen using cout. We can also
print variables of type int,double, and float and can control the number of
digits that appear aer the decimal point. For example, if we had a variable that
contained the value 3.14159265 we might only care about the first two numbers
aer the decimal point and just want to output 3.14 to the screen. We do that with
the precision() member function. is function call will result in subsequent
float or double variables being printed with the specified number of decimal
places. In the following code, the number of digits is set to 2:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
d o u b l e num = 3.14159265;
c o ut . p r e c i s i o n ( 2 ) ;
c o u t << num << e n d l ;
}
is code prints:
3.14
To display data in a similar way as a spreadsheet, we can create a field of
characters and set the number of characters in each field using the width() and
fill() member functions. Notice the use of the left flag in the following code,
which positions the output on the le side of the field; the default is for the output
to be on the right side:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
c o u t << ”Norwich” << e n d l ;
c o u t . w i dt h ( 1 5 ) ;
c o u t << ” U n i v e r s i t y ” << e n d l ;
c o u t . f i l l ( ’ * ’ ) ;
c o u t . w i dt h ( 2 0 ) ;
c o u t << l e f t << ” C or ps o f C a d e ts ” << e n d l ;
}
e above code prints:
Norwich
University
Corps of Cadets*****
5.1 Review estions
1. Which of the following is a correct way to output Hello World to the
screen?
(a) output: "Hello World";
(b) cout >> "Hello World";
(c) cout << "Hello World";
(d) console.output << "Hello World";
2. Which of the following is a correct way to output Hello! to the screen
on one line and Goodbye! to the screen on the next line?
(a) cout >> "Hello!" >> "Goodbye!";
(b) output: "Hello!\nGoodbye!";
(c) cout << "Hello!" << \n << "Goodbye!";
(d) cout << "Hello!" << '\n' << "Goodbye!";
3. Aside from the answer in the previous question, write two alternative ways
of printing Hello! and Goodbye! to the screen on two different lines.
4. Write several lines of code using the width() and fill() functions in a
main() that prints Programming! to the screen with 4 'x' characters
printed aer it.
5. Write code to output the values 124, 12.376, z, 1000000, and strings! as
distinct values, separated by spaces.
6. What is the output of the following program?
# i n c l u d e < i o s t r e a m >
# i n c l u d e < s t r i n g >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
s t r i n g s h i r t = ” maroon ” , p a n t s = ” b l u e ” ;
c o u t << s h i r t << ” ” << p a n t s << e n d l ;
r e t u r n 0 ;
}
5.2 Review Answers
1. c.
2. d.
3. cout << "Hello!" << endl << "Goodbye!"; or
cout << "Hello!\nGoodbye!";
(other similar answers are possible)
4.
c o u t . f i l l ( ’ x ’ ) ;
c o u t . w i dt h ( 1 6 ) ;
c o u t << l e f t << ”Programming ! ” ;
5. cout << 124 << " " << 12.376 << " z " << 1000000
<< " strings!";
6. maroon blue
5.3 Further Reading
• http://java-samples.com/showtutorial.php?tutorialid=245
Chapter 6
Input
When a programmer wants a user to enter data, such as the price of an item, he
or she will use the cin object, pronounced “see-in”, in conjunction with >>, the
extraction operator in the program. Let us look at the following code:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t x = 0 ;
c o u t << ” P l e a s e e n t e r a v a l u e f o r x : ” << e n d l ;
c i n >> x ;
return 0 ;
}
When you compile and run this code, here’s what the output will look like:
Please enter a value for x:
As a user you may want to check the value that was entered. To do this, simply
21
add an additional cout statement like this:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t x = 0 ;
c o u t << ” P l e a s e e n t e r a v a l u e f o r x : ” << e n d l ;
c i n >> x ;
c o u t << ” The v a l u e o f x i s : ” << x ;
r e t u r n 0 ;
}
e output of this code is:
Please enter a value for x:
Suppose the user enters a value of 1 for x. e output that follows is:
The value of x is: 1
As you can see, the value displayed is the one entered. is can be a very useful
technique in troubleshooting the values of variables throughout a program. Do not
be afraid to insert additional cout statements throughout a program to check the
values of variables when debugging. is can help in the debugging process and
speed up catching errors.
If you want to have a user input more than one value, just repeat the code for
each individual variable:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t x = 0 ;
i n t y = 0 ;
c o u t << ” P l e a s e e n t e r a v a l u e f o r x : ” << e n d l ;
c i n >> x ;
c o u t << ” P l e a s e e n t e r a v a l u e f o r y : ” << e n d l ;
c i n >> y ;
c o u t << ” The v a l u e o f x i s : ” << x << e n d l ;
c o u t << ” The v a l u e o f y i s : ” << y << e n d l ;
r e t u r n 0 ;
}
We can’t always trust that the user will input the correct data into a variable.
For example, if a user was prompted to input an age into a variable of type int
but typed the character z, the program would not behave properly because the user
entered the wrong data type. We can check for improper input like this by using the
cin.fail() function in a conditional statement. Look at the following code:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t x = 0 ;
i n t y = 0 ;
c o u t << ” P l e a s e e n t e r a v a l u e f o r x : ” << e n d l ;
c i n >> x ;
i f ( c i n . f a i l ( ) )
{
c o u t << ” T ha t i s n o t a v a l i d d a t a t y p e ! ” ;
}
}
is introduction to cin statements is only the beginning. ey will get slightly
more complicated aer we introduce strings, arrays, and overloaded operators.
6.1 Review estions
1. Which of the following numbered lines of code are proper cin statements?
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t x = 0 ;
i n t y = 0 ;
c o u t << ” P l e a s e e n t e r a v a l u e f o r x : ” ;
c i n << x ; / / #1
c i n >> x ; / / #2
c i n >> x / / #3
c i n x ; / / #4
c i n >< x ; / / #5
x >> c i n ; / / #6
r e t u r n 0 ;
}
2. Must you always use cin with cout? Why or why not?
3. What is the redirect operator, and how is it used to process user input?
4. Can you use cin to store a value in a variable that already has a value?
5. Write code that allows the user to enter an integer value and store it in a
variable. Your code should prompt the user, receive their input, and then
print their input value back to them.
6. Add some functionality to the code you wrote for the previous exercise. Add
two new variables, one char and one float or double. Prompt the
user properly for each value. e program should print out the values of the
variables, clearly labeled, on separate lines.
6.2 Review Answers
1. Only #2 (cin >> x;) is correct.
2. You do not need to to use cin statements exclusively with cout state-
ments, though it is good practice to provide adequate feedback to users.
3. e redirect operator is >>, and it is used in conjunction with cin on the
le and a variable on the right that receives the value entered by the user.
4. Yes, and the previous value is overwrien.
6.3 Further Reading
• http://www.cplusplus.com/reference/iolibrary
• http://www.cplusplus.com/doc/tutorial/basic_io
Chapter 7
Arithmetic
One of the most important things provided by C++ is the ability to do math. Ev-
erything a computer sees is a number. To a computer, its ability to do math and
manipulate numbers is as essential to it as breathing is to us. (My apologies to
anything not living that may be reading this).
e operators (+,-,*,/) in C++ are slightly different from what you may be
used to from your second-grade math class. Addition is still a plus sign ( +) and
subtraction is still a minus sign ( -). On the other hand, multiplication becomes an
asterisk ( *) and division becomes a forward slash ( /). ink of the forward slash
as over as in “5 over 9” is the same as the fraction 5/9 or 5
9.
To do math in C++, you will either want a variable to store the answer, or output
the answer to the user.
e following code directly outputs the answer to the user:
c o u t << 9 + 2 ; / / P r i n t s 11
is code shows how to use a variable to store the answer:
i n t sum = 9 + 2 ; / / sum now h o l d s 1 1
Note that when you use a variable to store an answer, the variable must come
first in the equation (before the equal sign) and must be the only thing on the le
side of the equation. ere are some other things to note. When you use more
complicated equations, you can use parentheses to help. C++ uses a familiar or-
der of operations (Parentheses, Exponents, Multiply, Divide, Add, and Subtract, or
PEMDAS), but without the exponent operation (this topic is covered in Chapter 17).
However, unlike in normal arithmetic, parentheses do not imply multiplication. For
25
example, (4)(3), which we might expect to mean “4 times 3” does not mean the
same as 4 * 3, the correct syntax. e expression (4)(3) results in a syntax
error and will not compile. e compiler returns an error message like this:
'error: '4' cannot be used as a function.'
In C++, there are several methods of shortening and simplifying the code you’re
creating. e first is the increment operator ( ++ ), which is found in the name of
the language, C++. is operator increases the value of the variable it’s applied to
by 1. Conversely, the decrement ( -- ) operator decreases the value by 1.
Keep in mind that order does maer with the increment and decrement opera-
tors. ey can be used as either prefixes or suffixes, but where you put the operator
results in slightly different behavior. Starting with similarities, C++ and ++C both
increase value of Cby one. e difference lies in when another variable is being set
to that incremented value, such as B = C++.Bwill be set to Cbefore Cis incre-
mented. B = ++C will cause Bto be set to C+1, in a similar way to B = 1 + C.
i n t A ;
A = 4 ;
A+ + ;
//A contains 5
i n t A ;
A = 9 ;
A−−;
//A contains 8
i n t A , B ;
B = 7 ;
A = B + + ;
//A contains 7, B contains 8
i n t A , B ;
B = 7 ;
A = ++B ;
//A contains 8, B contains 8
i n t A , B ;
B = 3 ;
A = B−−;
//A contains 3, B contains 2
Expression Equivalent to
A *= 3; A = A * 3;
B -= 5; B = B - 5;
C /= 10; C = C / 10;
Table 7.1: Examples of compound assignment updates
i n t A , B ;
B = 3 ;
A = −−B ;
//A contains 2, B contains 2
Compound assignment operators can decrease the amount you type and can
make your code more readable. ese are the operators +=,-=,*=, and /=. What
makes these operators special is that they use the value you want to change in the
operation. For example, x += 2 is equivalent to x=x+2.
Keep in mind the order that was used, as this becomes important with sub-
traction and division. e variable being changed is equivalent to the two lemost
variables in the longhand expression. Let’s say we have Xand Y, and want to set
Xequal to the value of Ydivided by the value of X. is is impossible with this
method, as X /= Y is equivalent to X=X/Y, and Y /= X is equivalent to
Y=Y/X.
Here is some sample code using the concepts we presented in this chapter:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t a = 5 , b = 1 0 , c = 1 5 , d = 2 0 ;
c o u t << ” a + b = ” << a + b << e n d l ;
c o u t << ” d −c = ” << d −c << e n d l ;
c o u t << ” a * b = ” << a * b << e n d l ;
c o u t << ” d / a = ” << d / a << e n d l ;
}
e output of this code is:
a + b = 15
d-c=5
a * b = 50
d/a=4
7.1 Review estions
1. Write a statement declaring two integer variables aand band initialize them
to 6 and 3, respectively.
2. Without changing the last line, fix the following code so there will be an
output of 12.
i n t a = 4 , b= 2 ;
a = a + 2 * b ;
c o u t << a ;
3. What is the output of the following code?
i n t a = 2 , b = 5 , c = 6 ;
a ++ ;
b = b * a ;
c = ( c −a ) + 3 ;
c o u t << a << e n d l ;
c o u t << b << e n d l ;
c o u t << c << e n d l ;
4. What is the output of the following code?
i n t a , b , c ;
a = 2 ;
b = 8 ;
c = 1 ;
c = b −b ;
c = a + a ;
c = b * 8 ;
b = b + b ;
c = a + c ;
b = a + b ;
a = a * c ;
b = a −c ;
c = b + a ;
c o u t << a << e n d l ;
c o u t << b << e n d l ;
c o u t << c << e n d l ;
5. What is the output of the following code?
i n t a = 4 , b = 2 , c , d ;
a = b + 3 ;
b ++ ;
c = ( b + 4 ) * 2 ;
c = c + 2 ;
d = a + b −3 ;
a ++ ;
a = a + 2 −b ;
b = b * 2 ;
c o u t << ” a= ” << a << e n d l ;
c o u t << ” b= ” << b << e n d l ;
c o u t << ” c = ” << c << e n d l ;
c o u t << ” d= ” << d << e n d l ;
6. What is the output of the following code?
i n t m = 3 , n = 2 , x , y ;
x = m + 5 ;
m−−;
y = (m + 4 ) / 3 ;
n = n + 2 ;
m = m + n / 2 ;
m+ + ;
x = x * 2 −3 ;
y = y * 2 ;
n = n + y * 3
c o u t << ”m= ” << m << e n d l ;
c o u t << ” n= ” << n << e n d l ;
c o u t << ” x = ” << x << e n d l ;
c o u t << ” y= ” << y << e n d l ;
7.2 Review Answers
1. inta=6,b=3;
2.
i n t a = 4 , b = 2 ;
a = ( a + 2 ) * b ;
c o u t << a ;
3. 3
15
5
4. 132
66
198
5. a=5
b=6
c=16
d=5
6. m=5
n=16
x=13
y=4
Chapter 8
Comments
As a C++ programmer, comments will make your life easier. ey are meant to
serve as notes, not just for you, but for anyone that may aempt to read your code.
To this end, comments are a quick explanation of the code. ere are two kinds of
comments, single-line comments and multi-line comments.
Single-line comments typically come aer a line of code. For a single-line com-
ment, simply type a double slash // at the end of the line, and follow it with what-
ever notes you like, preferably to explain what that line of code does. Alternatively,
the comment can start on a line of its own. Here are some examples:
i n t count ; / / Th i s v a r i a b l e was d e c l a r e d
/ / t o c o un t s o me t h in g
count = count + 1; / / I n c r e m e n t s c o un t by 1
/ / V a r i a b l e d e c l a r e d , and i n i t i a l i z e d t o p i
f l o a t l e n g t h = 3 . 1 4 1 5 9 ;
Multi-line comments, sometimes called block comments, are used when you
have a lot to say. ey begin with a slash star (/*) and are ended by a star slash
(*/). Here is an example:
/ *
* T h i s i s a
* m u l t i −line
*comment
* /
/ * Thi s i s a l s o a comment * /
33
Block comments do not need a star at the beginning of every line (as in the
preceding example), but many programmers write it anyways, because it makes it
easier to see and understand that “this is still a comment, don’t write code here.”
Some development environments will automatically color-code certain pieces of
code, so comments might be gray, for example, and the *at the beginning of each
line might be unnecessary in that case. However, someone else may use a different
development environment that does not use colors, so the stars can still improve
readability.
Keep in mind when commenting, the point is to be clear and concise. Try to
explain what’s happening as accurately as possible, but try to keep it short. As
you learn C++, use comments to explain what you’re doing and why. You have to
assume that the person reading your code needs an explanation for each non-trivial
line.
/ / Commenting a t t h e b e g i n n i n g o f t h e f i l e
/ / A ll ows you t o g i v e a summary o f y ou r pr ogr am
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
/ / Th is c o u t s t a t e m e n t o u t p u t s t o t h e s c r e e n
c o u t << ” H e l l o w or ld ” << e n d l ;
c o u t << ” What ’ s t h e d a t e ? ” << e n d l ;
/ / Comments s h ou ld be u se d t o e x p l a i n t h i n g s t h a t may
/ / n o t be o b v i o u s t o some one o t h e r t ha n you
c i n >> d a t e ; / / T a ke s t h e d a t e f rom t h e u s e r
/ *
* You can a l s o u s e comments t o remin d y o u r s e l f of
* c h an g e s you want t o make , e . g .
* ” deb ug c ode p a s t t h i s p o i n t ”
* /
r e t u r n 0 ;
}
8.1 Review estions
1. Comment each line of this code:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t time ;
c o u t << ” E n t e r t i m e \ n ” ;
c i n >> t im e ;
i n t answer = ( 3 2 * t i m e * ti m e ) / 2 ;
c o u t << ” The d i s t a n c e i s ” ;
c o u t << a ns we r ;
c o u t << ” s e c o n d s \ n ” ;
r e t u r n 0 ;
}
2. Fix this code by removing or modifying comments so that it runs and com-
piles as it should.
/ * # i n c l u d e < i o s t r e a m > i n c l u d e s t h e i o s t r e a m *
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t t ime ; / / A p l a c e t o s t o r e t he t im e
c ou t << ” E n te r t im e \ n ” ; / / Ask t o e n t e r t h e t ime
c i n >> t im e ; / / T ak es u s e r i n p u t
i n t answer = ( 3 2 * t im e * t i me ) / 2 ; / / C a l c u l a t e s i t
c o ut << ” The d i s t a n c e i s ” ; / * O ut pu ts
c o u t << a ns we r ; t h e d i s t a n c e
c o u t << ” s e c o n d s \ n ” ; i n s e c o n d s * /
r e t u r n 0 ;
}
3. Explain the purpose of commenting. How does it help you? Why would
someone else need to be able to understand your code?
4. Write and properly comment your own simple program.
5. Go back to the program you wrote from the previous question. Add further
comments that explain what’s happening and share the commented code
with a classmate or friend. Ask them if they understand what’s happening
from just the comments.
6. Add comments to the following code.
Note: Save percentages in hockey are shown to three decimal places and not
multiplied by 100: .900 instead of 90%.
# i n c l u d e < i o s t r e a m >
# i n c l u d e <cstdlib >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
double s h ot s , g o a ls , s a ve s , s a v e _ p e r c ;
char c o n t ;
do {
c out . u n s e t f ( i o s : : f i x e d ) ;
c out . u n s e t f ( i o s : : s ho wp oi nt ) ;
c o u t << ” E n t e r t h e number o f s h o t s on g o a l : \ t ” ;
c i n >> s h o t s ;
c o u t << ” E n t e r t h e number o f g o a l s s c o r e d : \ t ” ;
c i n >> g o a l s ;
c o u t << e n d l ;
s a v e s = s h o t s −g o a l s ;
s a v e _ p e r c = ( s a v e s / s h o t s ) ;
c o u t << ” I f t h e r e were ” << s h o t s << ” s h o t s and ”
<< g o a l s << ” g o a l s \ n ” ;
c o u t << ” th en t he g o a l i e ’ s s a v e p e r c e n t a g e was ” ;
c o u t . s e t f ( i o s : : f i x e d ) ;
c o u t . s e t f ( i o s : : s h o wp o i nt ) ;
c o ut . p r e c i s i o n ( 3 ) ;
c o u t << s a v e _ p e r c << e n d l << e n d l ;
c o u t << ” Run a g a i n ? Y / N\ t ” ;
c i n >> c o n t ;
c o n t = t o u p p e r ( c o n t ) ;
}while ( c o n t == ’ Y ’ ) ;
r e t u r n 0 ;
}
8.2 Review estions
1. Answers will vary
2.
# i n c l u d e < i o s t r e a m > / * i n c l u d e s t he i o s t r e a m * /
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t time ; / / A p l a c e t o s t o r e t he t im e
c o u t << ” E n t e r t i m e \ n ” ;/ / Ask t o e n t e r t he t ime
c i n >> t im e ; / / T ak es u s e r i n p u t
i n t answer = ( 3 2 * t i m e * ti m e ) / 2 ; / / C a l c u l a t e s i t
c o u t << ” The d i s t a n c e i s ” ;// Outputs
c o u t << a ns we r ; / / t he d i s t a n c e
c o u t << ” s e c o n d s \ n ” ;/ / i n s e c o n d s
r e t u r n 0 ;
}
3. Comments help you check that you know what you’re doing and make sure
you are doing everything that needs to be done. ey also help other people
understand your code, which is especially useful if your logic is different
from theirs.
4. Answers will vary.
5. Keep trying until someone else understands the code from the comments
alone.
6. Answers will vary.
Chapter 9
Data Types and
Conversion
Suppose you need to carry two products across a farmyard: apples and water. e
container you choose would depend on the product, and how much of the product
you have to move. You might choose a small hand basket to carry a few apples,
and a larger bushel basket to carry a large number of apples. Similarly, you could
use a one-gallon bucket or a five-gallon bucket, depending on how much water you
expected to move.
In a similar way, we choose data types to describe the type of data we would
like to store in a variable, and “how much” of that data we expect to store.
Every variable has a data type which describes the range of possible values
that may be stored in the variable. e C++ language defines a handful of basic
types, some of which were discussed in Chapter 4. ese types, their sizes (which
may vary depending on the operating system), and the range of possible values
can be found in Table 9.1. Additionally, the C++11 standard provides for the long
long int data type as described in Table 9.2.
Several of the integer types have unsigned versions, which may only contain
values greater than or equal to zero. e floating-point types do not have un-
signed versions, as the sign is part of the standard that defines how these variables
are represented in memory.
39
bool 1 byte true or false
char 1 byte −128 to 127
short int (short) 2 bytes −32,768 to 32,767
int 4 bytes −2,147,483,648 to
2,147,483,647
long int (long) 4 bytes −2,147,483,648 to
2,147,483,647
float 4 bytes See “Floating-point Types”
below
double 8 bytes See “Floating-point Types”
below
long double 8 bytes1See “Floating-point Types”
below
Table 9.1: Common data types and their ranges of values
Type Size Range of Values
long long int
(long long)
8 bytes −9,223,372,036,854,775,808
to 9,223,372,036,854,775,807
Table 9.2: C++11’s long long int data type
9.1 Floating-point types
Floating-point types are used to represent numbers that are not whole integers. For
example:
f l o a t f = 3 . 3 5 ;
Variables of type float and of type double store these numbers in similar
components as scientific notation, so the above value could be represented as 335×
10−2. e first part, 335, (sometimes called the coefficient or significand) is stored
separately from the second part, −2, (called the exponent). e types can represent
1Along double might be stored as an 80-bit extended precision type, but
this is dependent on the compiler. Variables of this type will be at least as large as
adouble.
Type Size Range of Values
unsigned char 1 byte 0to 255
unsigned short 2 bytes 0to 65,535
unsigned int 4 bytes 0to 4,294,967,295
unsigned long 4 bytes 0to 4,294,967,295
unsigned long long28 bytes 0to
18,446,744,073,709,551,615
Table 9.3: Unsigned types
Type Exponent Range Significand Range
float 0to 255 223:8,388,608 possible values
double 0to 2,048 252:4,503,599,627,370,496
possible values
long double 0to 2,048 252:4,503,599,627,370,496
possible values
Table 9.4: Floating point types
different ranges of significand and exponents, as shown in Table 9.4.
In fact, we can use scientific notation in conjunction with floating-point vari-
ables. e previous code that assigned a value to fcan also be wrien as:
f l o a t f = 3 35 e −2; / / S e t s f t o 3 . 3 5
Both float and double include a few special values that represent non-
numeric results, such as infinity, negative infinity, and NaN (Not a Number).
f l o a t g = 1 0 . 0 / 0 . 0 ; / / g i s s e t to i n f i n i t y
f l o a t h = g * −1.0 ; / / h i s s e t t o n e g a t i v e i n f i n i t y
f l o a t i = g / h ;
/ / S i n c e i n f i n i t y d i v i d e d by n eg a t iv e i n f i n i t y i s
/ / un d e fine d , th e r e s u l t o f t h e d i v i s i o n i s not a
/ / number , an d i i s s e t t o NaN
2is data type is found in the C++11 standard.
9.2 Other types introduced by C++11
C++11 provides the cstdint library, which defines several additional types that
may be convenient. ese types are listed in Table 9.5.
Type Purpose Unsigned version
intmax_t e integer of maximum size
supported on the platform
uintmax_t
int8_t An integer of exactly 8 bits uint8_t
int16_t An integer of exactly 16 bits uint16_t
int32_t An integer of exactly 32 bits uint32_t
int64_t An integer of exactly 64 bits uint64_t
Table 9.5: Data types found in C++11’s cstdint library
ese types are provided in part because the basic types like int and short
are not guaranteed to be of any particular size, which can cause problems when
compiling the same code on different platforms.
9.3 Conversion Between Types
It is sometimes necessary to convert a variable of one type to another, perhaps in
order to pass the variable to a function that doesn’t support the variable’s original
type. Here is an example of a variable of type int being converted (automatically)
to a double:
i n t x = 2 ;
double y ;
y = x ; / / Type c o n v e r s i o n : t h e i n t e g e r 2 i s c o n v e r t e d
/ / t o t h e d o u b l e 2 . 0
c o u t << ” y = ” << y << e n d l ; / / T h is p r i n t s y = 2
is example demonstrates a widening conversion, since any possible value
of xcan be represented in y. On the other hand, we can do the reverse conversion:
i n t x ;
double y = 2 . 0 ;
x = y ; / / Type c o n v e r s i o n : t h e d o u bl e 2 . 0 i s c o n v e r t e d
/ / t o t h e i n t 2
c o u t << ” x = ” << x << e n d l ; / / T h is p r i n t s x = 2
is code compiles and runs, but the compiler produces the following warning:
warning: converting to 'int' from 'double'
e compiler has a good reason for this warning: not all possible values that
can be represented in a double can be represented in an int. We refer to this as a
narrowing conversion. If we change the code slightly, we can see where problems
can occur:
i n t x ;
double y = 2 . 9 ;
x = y ; / / Type c o n v e r s i o n : t h e d o u bl e 2 . 9 i s c o n v e r t e d
/ / t o t h e i n t 2
c o u t << ” x = ” << x << e n d l ; / / T h is p r i n t s x = 2
Because integers cannot represent the numbers aer the decimal point, they are
simply dropped. is might seem counterintuitive, as we might expect the values to
be rounded up from 2.9 to 3. Fortunately, C++11 provides a round() function
in the <cmath> library that returns the integer closest to the passed parameter:
i n t x ;
double y = 2 . 9 ;
x = round ( y ) ;
/ / round ( y ) r e t u r n s t he d ou bl e 3 . 0 ( t he c l o s e s t i n t e g e r
/ / t o t h e p a s s e d p a r a m e t e r ) T h i s d o u b l e i s t he n
/ / c o n v e r t e d t o t h e i n t 3
c o u t << ” x = ” << x << e n d l ; / / T h is p r i n t s x = 2
9.4 Coercion & Casting
e examples in the previous section relied on the compiler to perform the con-
versions from int to double and double to int. is implicit, automatic
conversion is oen referred to as coercion, and can be found in the following ex-
ample:
i n t z = 3 . 3 + 4 . 8 ; / / z i s s e t t o th e i n t e g e r 8
/ / ( c o e r c e d f rom t h e d o u b l e 8 . 1 )
e compiler still warns us that it is converting the double to an int. In
this case, we know that we want an integer value, so we can tell the compiler to
explicitly convert the doubles to ints using explicit casts, as follows:
i n t z = ( int ) 3 . 3 + ( i n t ) 4.8; / / z i s s e t t o 7
We enclose the “target” type in parentheses (in this case, int) and place it
before the value or expression we want to convert. Doing this removes the warning
that the compiler produces when it coerces the double to int. e above still
isn’t quite what we want, though, since the individual doubles are converted to 3
and 4, respectively. (Remember that converting from a double to an int drops
the part aer the decimal point rather than rounding!) It would be beer to convert
the result of the addition, rather than the individual values, like this:
i n t z = ( int ) ( 3 . 3 + 4 . 8 ) ; / / z i s s e t t o 8
9.5 Automatic Types in C++11
C++11 introduces the auto data type, which leaves the determination of a vari-
able’s type up to the compiler. At compile time, the data type of the value that is
assigned determines the data type that replaces the auto type. Some of the syntax
in the second line below may be unfamiliar—for a description of what’s happening
there, refer to Chapter 19.
au t o myVar = 3 ; / / myVar i s an i n t
au t o myVar2 = &myVar ; / / myVar2 i s an i n t *
au t o myVar3 = ’ t ’ ;/ / myVar3 i s a c ha r
e decltype operator is another new feature, which extracts types from
objects and is used in a similar way as auto:
au t o myVar = 3 ; / / myVar i s an i n t
d e c l t y p e ( myVar ) myVar4 ; / / myVar4 i s an i n t
d e c l t y p e ( myVar < 1 ) myVar5 ; / / myVar5 i s a b o o l
In these examples, it is easy to determine the types assigned to the variable,
but the power of auto is in conjunction with complicated types like iterators of
container objects as discussed more in Chapter 23. Here is an example:
s t d : : v e c t o r < int > v ; / / C re at e a v e c t o r o f i n t e g e r s
v . p u s h _ b a c k ( 2 ) ; / / Add an e le men t c o n t a i n i n g 2 t o t he v e c t o r
v . p u s h _ b a c k ( 8 ) ; / / Add an e le men t c o n t a i n i n g 8 t o t he v e c t o r
au t o m y I t e r a t o r = v . b e gi n ( ) ;
/ / The above i s e q u i v a l e n t to :
/ / s t d : : v e c t o r < i n t > : : i t e r a t o r m y I t e ra t o r = v . be g i n ( ) ;
9.6 Review estions
1. What’s the difference between the various data types that store numbers?
Why would you use one over the other?
2. If you assign the result of an int divided by an int to a float (e.g.
float num = 13/7;), what could happen to the resulting value?
3. Declare a variable named sampleSize and set it to 14.58093.
4. Write code that increases sampleSize by 12.495.
9.7 Review Answers
1. ints only store whole numbers. floats and doubles can store num-
bers with decimal points. ints are useful for anything that cannot have
fractional parts, and you might also use a double for very large numbers.
2. e fractional part is le off. (num is 1 in the example)
3. double sampleSize = 14.58093;
4. sampleSize += 12.495;
9.8 Further Reading
• http://www.cplusplus.com/reference/cstdint/
• http://en.wikipedia.org/wiki/Floating_point
• http://en.wikipedia.org/wiki/IEEE_floating_point
• http://learncpp.com/cpp-tutorial/25-floating-point-numbers/
Chapter 10
Conditionals
Conditionals are used to direct the program to different sections of code. In plain
English, we might have a statement “If X is greater than Y, do this…” Conditionals
direct the program to behave differently depending on the results of a comparison.
Several common comparison operators used in C++ are:
Symbol Meaning
== Is equal to
!= Is not equal to
>= Greater than or equal to
<= Less than or equal to
>Greater than
<Less than
&&,and Logical AND: e condition on the le AND the condition
on the right must be true
||,or Logical OR: e condition on the le OR the condition on
the right must be true
Table 10.1: Common comparison operators
47
10.1 if,else, and else if
e most popular conditional is the if statement. An if statement looks like this:
i f ( v a r i a b l e == v a r i a b l e 2 )
{
/ / Code h er e e x e c u t e s o nl y when
/ / t h e v al ue of v a r i a b l e i s th e same a s v a r i a b l e 2
}
e keyword if is used to start the statement. Parentheses are used to contain
the conditional expression. If the expression inside the parentheses is true, then the
following expression will be executed.
10.1.1 A small digression on expressions
Note that curly braces merely surround expressions to become a single expression.
e act of surrounding expressions creates a code block. However, having only one
expression within a code block is the same as not having it in a code block.
i f ( v a r i a b l e == v a r i a b l e 2 )
{
c o u t << ” Yes ! ” ;
}
is the same as
i f ( v a r i a b l e == v a r i a b l e 2 )
c o u t << ” Yes ! ” ;
It is not recommended to go without braces for mere brevity at the cost of
making mistakes later on. For example, suppose you have some code for baking
bread, like the following.
i f ( b re ad Type == 1 0 )
ovenFanOn = t r u e ;
en later you are told that bread type 10 needs to be cooked at 350 ◦F. So you
make the following change:
i f ( b re ad Type == 1 0 )
ovenFanOn = t r u e ;
ovenTemp = 3 5 0 ;
int a = 0; if var1 == var2
True
False
a = 1;
donea = 2;Else
No Else
Figure 10.1: if and else statement flow of execution
Except that is really the same as:
i f ( b re ad Type == 1 0 )
ovenFanOn = t r u e ;
ovenTemp = 3 5 0 ;
Now the baker is upset because every loaf is being cooked wrong except bread
of type 10! What you really meant was:
i f ( b re ad Type == 1 0 )
{
ovenFanOn = t r u e ;
ovenTemp = 3 5 0 ;
}
Here’s another bear trap that you’ll likely hit:
i f ( b re ad Ty pe == 9 ) ;
ovenFanOn = t r u e ;
It is still valid syntax, but the expression aer the if statement is an empty
expression. An empty expression does nothing, and so now every bread type will
have the fan on, which is not what the baker wanted.
10.1.2 Using else
An else statement may be placed aer an if statement, and any time the expres-
sion inside the parentheses following the if is not true, the code inside the else
block is executed. For example:
i n t a = 0 ;
i f ( v a r 1 == v a r 2 )
{
/ / Code h er e e x e c u t e s o nl y when
/ / t h e v al ue of v a r i a b l e i s th e same a s v a r i a b l e 2
a = 1 ;
}
else
{
/ / Code h er e e x e c u t e s i f t he y a r e n ot t h e same
a = 2 ;
}
An else statement is used when you want some code to execute in any other
case where the if statement is not true. An example of how this works is also
shown in Figure 10.1.
An else if could also be placed aer the if statement. An else if is
an additional if statement checked only when the previous if statement is false.
While else is a catch-all, else if chains an if to test for other conditions.
Multiple else if statements can be used, and they are all checked sequentially,
and if necessary, an else statement can be included at the end as a final catch-all.
Take a look at Figure 10.2 for a flowchart example.
Here’s what the three statements would look like all together:
i f ( a == b )
{
c o u t << ” They a r e t h e same ! ” << e n d l ;
}
e l s e i f ( a > b )
{
c o u t << ” a i s b i g g e r ! ” << e n d l ;
}
else
{
c o u t << ” a i s s m a l l e r ! ” << e n d l ;
}
Note that every conditional expression is in parentheses. Each if must be
followed by a (...) (with a Boolean expression inside the parentheses) in C++.
Conditional expressions also appear in loops (discussed in Chapter 12) and switch
statements.
start if (a == b)
Outputs "They are the same!"
true else
false
if (a > b)
Outputs "a is bigger"
true else
false
Outputs "a is smaller"
Figure 10.2: How if-else chaining works
10.2 switch statements
switch statements (also sometimes called switch-case statements) make a
menu-like set of blocks. It does the same job as many if statements, but can sim-
plify the job when used correctly. Here is an example:
switch ( v a r i a b l e ) :
{
c a s e 1 :
/ / c ode t o e xe cu t e when v a r i a b l e i s e q ua l t o 1
break ;
c a s e 2 :
/ / c ode t o e xe cu t e when v a r i a b l e i s e q ua l t o 2
break ;
default :
/ / c ode t o e xe cu t e when v a r i a b l e i s n e i t h e r 1 nor 2
break ;
}
/ / Resume h er e a f t e r a b r e ak
If variable is equal to 1 then the code following case 1: will be executed.
If it is equal to 2, then the code following case 2: will be executed, and if it is
equal to neither, then the code following default: will be executed. e cases
are separated by the break statement, which forces the code to leave the switch
statement’s block of code. is code:
switch ( v a r i a b l e )
{
c a s e 1 :
c o u t << ” You p i c k e d c a s e 1 . Lame . ” ;
break ;
c a s e 2 :
c o u t << ” Case two i s way b e t t e r . ” ;
break ;
default :
c o u t << ”WRONG! ” ;
break ;
}
is equivalent to this code:
i f ( v a r i a b l e == 1 )
{
c o u t << ” You p i c k e d c a s e 1 . Lame . ” ;
}
e l s e i f ( v a r i a b l e == 2 )
{
c o u t << ” Case two i s way b e t t e r . ” ;
}
else
{
c o u t << ”WRONG! ” ;
}
When there are only a few cases, if,else if, and else statements are
oen easier. However, when you get to a greater number of cases, switch state-
ments become easier.
In switch statements, only one case’s code executes, provided that each
case is followed by break. Otherwise, the program continues execution until
it reaches a break statement or the end of the switch block. With an if and
else if, only one branch may be executed, and the condition in the else if
is only evaluated if the condition in the if is false.
Here is some code that uses both switch and if statements. Compiling and
running the following code results in the output in Table 10.2.
User enters Output
//Program start <1> Addition
<2> Subtraction
<3> Compare
Type the number of your desired option:
1e result of this addition is 9.3
2e result of this subtraction is 0.9
3A is greater than B
//anything
other than 1,
2, or 3
Not an option
Table 10.2: e sample program’s output
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( ) {
i n t c h o i c e ;
d o u b l e a = 5 . 1 , b = 4 . 2 ;
c o u t << ” <1> A d d i ti on \ n<2> S u b t r a c t i o n \ n<3> Compare \ n ” ;
c o u t << ” Type t h e number o f y ou r d e s i r e d o p t i o n : \ t ” ;
c i n >> c h o i c e ;
switch ( c h o i c e ) {
c a s e 1 :
c o u t << ” The r e s u l t o f t h i s a d d i t i o n i s ”
<< a + b << e n d l << e n d l ;
br e a k ;
c a s e 2 :
c o u t << ” The r e s u l t o f t h i s s u b t r a c t i o n i s ”
<< a −b << e n d l << e n d l ;
br e a k ;
c a s e 3 :
i f ( a > b )
c o u t << ”A i s g r e a t e r t ha n B ” ;
e l s e i f ( a < b )
c o u t << ”A i s l e s s t h an B ” ;
e l s e / / a == b
c o u t << ”A e q u a l s B ” ;
br e a k ;
default :
c o u t << ” Not an o p t i o n ” ;
br e a k ;
}
return 0 ;
}
10.3 Review estions
1. What is the output of the following code?
i n t a = 5 ;
i n t b = 1 0 ;
i f ( a > b )
c o u t << ” a i s g r e a t e r than b . ” ;
e l s e
c o u t << ” b i s g r e a t e r than a . ” ;
2. Why are switch statements useful?
3. When are braces ({}) needed in an if statement?
4. Write a program that checks which number is higher than another and prints
out an appropriate message. is program should use 2 variables, an if
statement and an else statement. Bonus: Rewrite it to also check if the
numbers are equal.
10.4 Review Answers
1. b is greater than a.
2. switch statements are useful for making menus for the user. (Other an-
swers are also possible)
3. Braces are needed for any code longer than 2 lines following an if.
4.
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t i n pu t1 , i n p u t 2 ;
c o u t << ” e n t e r a number : ” ;
c i n >> i n p u t 1 ;
c o u t << ” e n t e r a number t o comp are t o t he f i r s t : ” ;
c i n >> i n p u t 2 ;
i f ( i n p u t 1 > i n p u t 2 )
c o u t << i n p u t 1 << ” i s g r e a t e r than ” << i n p u t 2 ;
e l s e
c o u t << i n p u t 2 << ” i s g r e a t e r than ” << i n p u t 1 ;
}
Chapter 11
Strings
Let’s discuss strings. A string is a data type typically used to hold a collection
of printable characters such as words, sentences, or longer sequences. In order to
use strings in your program you must first include the string library:
# i n c l u d e <string >
u s i n g n am es pa ce s t d ;
Also note that a string, for convenience, can be treated like an array of individual
characters.
When we declare variables of type string, we declare them just like we
would an int,float, or double. We can create a variable named myString
of type string by doing this:
# i n c l u d e <string >
u s i n g n am es pa ce s t d ;
s t r i n g m y S tri n g ;
If you choose not to have using namespace std; in your code, the variable
myString must be declared as follows:
# i n c l u d e <string >
s td : : s t r i n g mySt r i ng ;
We can then store anything we want in that string as long as it is made up of
characters. When a literal value is assigned to a string, it should be surrounded
55
by double quotes such as in the case of "Hello":
# i n c l u d e <string >
s t r i n g m y S tri n g = ” H e l l o ” ;
If we are storing the value of a string entered by a user, the user does not
have to use quotes. We can store "Hello" in the string by doing the following:
s t r i n g m y S tri n g ;
c i n >> m ySt ri n g ; / / U se r t y p e s : H e l l o
/ / m y S tr i ng i s now ” H e l l o ”
It is also possible to use the arithmetic operator +with strings to concatenate (com-
bine) the two strings. If we combined one string that contained "Hello" and
another string that contained "World" the connected string would then read
"HelloWorld".
s t r i n g v1 = ” H e l l o ” ,
v2 = ”World” ;
c o u t << v1 + v 2 << e n d l ;
/ / O utp u t s :
/ / H e lloWorl d
In order to have a space between the two words, one of the strings would need to
contain a space such as this:
s t r i n g v1 = ” H e l l o ” , v2 = ” World ” ;
/ /−−−−−−−−−−−−−−−−−−−−−−−−−^−−−−−−−
c o u t << v1 + v 2 << e n d l ;
/ / O utp u t s :
/ / H e l l o World
Or it can be represented as:
s t r i n g v1 = ” H e l l o ” , v2 = ” World ” ;
/ /−−−−−−−−−−−−−−−−^−−−−−−−−−−−−−−−−
c o u t << v1 + v 2 << e n d l ;
/ / O utp u t s :
/ / H e l l o World
Alternatively, a space can be added like so:
s t r i n g v1 = ” H e l l o ” , v2 = ”World ” ;
c o u t << v1 + ” ” + v2 << e n d l ;
/ /−−−−−−−−−−−−^−−−−−−−−−−−−−−−−−−−
/ / O utp u t s :
/ / H e l l o World
e first two concatenates the two strings to create one string that contains “Hello
World”, and the third concatenates three strings to produce the same result.
When reading strings from std::cin, the default behavior is to collect all
characters until the first whitespace (a tab, space, or newline) character that it finds
in the input. For example, if the user inputs “Hello World” in the following code,
std::cin stops reading at the first whitespace, and thus the string would con-
tain only “Hello”. If we want to read the entire line of text, we need to use the
getline() function, which reads until the first newline character. is is how
you use the getline() function:
s t r i n g m y S tri n g ;
g e t l i n e ( cin , my S t rin g ) ;
is function call will take the entire line of input, including all whitespace charac-
ters, and store it in the variable myString.
We can also find out the length of the string by using the member function
length() with any string object. For example, if we wanted to find the length
of a string entered by a user and store it in a variable named stringLength,
we might do this:
s t r i n g m y S tri n g ;
i n t stringLength ;
g e t l i n e ( cin , my S t rin g ) ;
s t r i n g L e n g t h = my St ring . l e n g t h ( ) ;
c o u t << ” The s t r i n g you e n t e r e d was ”
<< stringLength
<< ” c h a r a c t e r s lon g . ”
<< e n d l ;
Aside from finding the length of a string, we can search for certain characters in the
string by using the find() and rfind() member functions. For example, if we
wanted to find a single space in a string variable named myString that contains
“Hello World”, we would do this:
s t r i n g m y S tri n g = ” H e l l o World ” ;
i n t sp o t = m yS tring . f i n d ( ” ” ) ;
H e l l o W o r l d
0 1 2 3 4 5 6 7 8 9 10
myString
Figure 11.1: A string viewed as an array
is code results in the value 5 being stored in the variable named spot be-
cause the space character is stored at index 5 if you treat the string as an array, as
shown in Figure 11.1.
Remember that we start at index 0, so even though the space is in the sixth
position, it is at index 5 in the string. When a line of text is stored in a string, think of
it as being stored in memory in an array of the same length as there are characters in
the string. For example, the string "Hello World" can be contained in an array
with 11 slots, therefore the space character would be found in myString[5].
e find() function can also search within a string from some arbitrary starting
point, instead of from the beginning:
s t r i n g m y S tri n g = ” H e l l o World ” ;
i n t s po t , s p o t 2 ;
s p o t = m y St r ing . f i n d ( ” ” ) ; / / Fo und a t i n d e x 5
/ / S t a r t i n g f rom i n d e x 5 , f ou n d a t i n d e x 7
s p o t 2 = m y St r ing . f i n d ( ” o ” , s p o t ) ;
e second argument that is passed to the function (in this case, spot) is the index
at which you want to start your search.
We can also use the rfind() function to find a character in reverse direction
from the end of the string, or from some starting point, as above. If we wanted to
find the single character string "o" before the space we might do something like
this:
s t r i n g m y S tri n g = ” H e l l o World ” ;
i n t s po t , s p o t 2 ;
s p o t = m y St r ing . r f i n d ( ” ” ) ; / / fo u nd a t i n d e x 5
/ / s t a r t i n g fr om i n d e x 5 , f ou n d a t i n d e x 4
s p o t 2 = m y St r ing . r f i n d ( ” o ” , s p o t ) ;
is function call to rfind() uses the arguments "o" and spot. is stores
the position of the first "o" it comes across aer going in reverse from the index
stored in spot (which contains 5). e last line would be equivalent to:
/ / s t a r t i n g fr om i n d e x 5 , f ou n d a t i n d e x 4
s p o t 2 = m y St r ing . r f i n d ( ” o ” , 5 ) ;
Both of these function calls will start searching for the string "o" backwards from
the same spot in the string, at index 5.
Sometimes the string you search for cannot be found, as in this example:
s t r i n g m y S tri n g = ” H e l l o World ” ;
i n t sp o t = m yS tring . f i n d ( ”Q” ) ; / / No Q i n t h i s s t r i n g !
In this case, the find() (or rfind(), for that maer) returns a special value
named string::npos. When we use find() or rfind() and believe that
they could fail, we should verify that the string was found, as below:
s t r i n g u s e r I n p u t ;
i n t s p o t ;
c i n >> u s e r I n p u t ;
s p ot = u s e r I n p u t . f i n d ( ”Z” ) ;
i f ( s p ot == s t r i n g : : npos )
c o u t << ” T h er e was no Z i n what you t y p e d ! ” << e n d l ;
else
c o u t << ” The f i r s t Z was i n p o s i t i o n ” << s p o t << e n d l ;
11.1 Review estions
1. Write code to declare a string and take input from a user.
2. Can a string be treated as a character array?
3. When do you use a string?
4. What is the #include needed to use strings?
5. What function do you have to use to take an input with a space?
6. Write code that takes in 5 words and outputs each of them 4 times.
7. Write a program that takes in an input of at least two words of the same
length. e program should then switch the last word and the first word.
11.2 Review Answers
1.
s t r i n g m y S tri n g ;
c o u t << ” P l e a s e i np u t a s t r i n g : ” ;
g e t l i n e ( cin , my S t rin g ) ;
/ / c in >> m yStri n g ; i s a l s o a c c e p t a b l e
2. Yes
3. When you need to hold a collection of printable characters such as words,
sentences, or longer sequences.
4. #include <string>
5. getline
6.
s t r i n g m y S tri n g ;
c o u t << ” P l e a s e i np u t a s t r i n g : ” ;
g e t l i n e ( cin , my S t rin g ) ;
/ / c in >> m yStri n g ; i s a l s o a c c e p t a b l e
11.3 Further Reading
• http://www.harding.edu/fmccown/cpp_strings.pdf
• http://www.stanford.edu/class/cs106x/handouts/08-C++-Strings.pdf
Chapter 12
Loops
12.1 Introduction
Okay, so you know how to do some programming, but now you need to be able to
handle a dozen or more operations that are obnoxiously repetitive. Imagine that you
have a program that needs to allow data to be entered about your employees. Do
you really want to have to write out the code to do that for every single individual?
No—you want to set it up so you write it out as concisely as possible, and copy and
paste just won’t work. What we need to do is write the relevant code once and have
it repeated for us as many times as necessary.
For this, we’ll use a structure known as a loop, which does exactly what you
expect it would. A loop allows you to repeat a section of code as many times as you
need. When the code reaches the end of the section, it goes back to the top of the
section and the loop starts again. Aer each repetition of the loop (which we call an
iteration), it will check for an end condition that is specified by the programmer.
12.2 Having Fun while Programming
e first loop we’ll cover is the while loop, probably the simplest and easiest-to-
use loop. It’s referred to as a pretest loop as it’s designed to check the loop’s end
condition prior to a repetition of the loop.
In Figure 12.1, the basic model of a pretest loop is shown. A diamond is used
to represent where a decision must be made. In this case, it’s a Boolean expression.
If the expression is true, control passes to the rectangle, which represents an action
(or actions) to be performed: the statements that represent the body of the loop.
61
Figure 12.1: Logic of a while loop
As with everything else we’ve learned so far, syntax is important. e structure
is simple enough, as the pseudocode below shows:
while ( BooleanExpression )
{
statement ;
statement ;
/ / wh at e v e r e l s e n e e ds t o be done
}
e important thing to remember here is to be sure you have some statement
to eventually allow the loop to exit. When the Boolean expression is false, re-
member, the loop is finished.
Also, note that, like an if statement, the braces are not necessary if there
is only one statement following the line with the while keyword and Boolean
expression. Is it recommended to use the braces with only one statement? For your
own sanity, and that of others reading your code, yes. Do you have to? No, but
some organizations’ coding standards might say otherwise, because it makes the
code easier to read and edit. So remember, it’s best to start with good habits early.
Let’s look at an actual example of a while loop.
i n t i = 1 0 ; / / i n i t i a l i z e s i a t 10
c o u t << ”T−minus ” ;
/ / w h i l e l o o p t h a t i s e nd ed when i i s l e s s t ha n 0
while ( i > = 0 )
{
/ / o u t p u t s t h e v a l u e o f i , t h en moves t o a new l i n e
c o u t << i << e n d l ;
/ / d e c r e a s e s th e v a lu e o f i by 1
i−−;
} ;
c o u t << ” L i f t O f f ! ” ;
e above code prints a countdown:
10
9
8
7
6
5
4
3
2
1
Lift Off!
12.3 do-while Loops
Remember how the while loop is known as a pretest loop? Well, a do-while
loop is known as a post-test loop for a similar reason. Let’s take a look at the
flowchart in Figure 12.2 and take a guess as to why.
Post-test loops perform the statements in the body of the loop before it tests
the end condition. Let’s look at how this will affect the syntax you will use when
implementing the loop.
Figure 12.2: Logic of a do-while loop
do
{
something ;
something ;
/ / wh at e v e r e l s e n e e ds t o be done
}w h i l e ( BooleanExpression )
e difference between a while and a do-while loop is where each checks
its end condition. In this case, the line with the while and the end condition are
aer the main section of code. In a normal while loop, the program can potentially
meet the end condition before even entering the loop body, and just pass over it. In
ado-while loop, the program checks the end condition aer each iteration of the
loop, so it will run at least once before the loop ends.
ere’s not a whole lot more to add then hasn’t been stated in the while loop
section, so here’s an example.
char cont ; / / S h o r t f o r c o n t i n u e ;
/ / c o n t i n u e i s a ke y word and can ’ t be u sed
do {
c o u t << ” Go C a de ts ! \ n ” ;
c o u t << ” Do you want t o c o n t i n u e ? Type Y f o r y es : \ t ” ;
c i n >> c o n t ;
}w h i l e ( c o n t == ’ Y ’ ) ;
12.4 Event-Based Loops vs Count-Based Loops
Loops can be organized into two categories based on how you use them. ese two
categories are defined by if you want to do a certain number of iterations of the loop
(a count-controlled loop) or continue until some event occurs, such as a particular
user input (an event-controlled loop). Let’s look at code examples to differentiate
the two. e first example shows an event-controlled while loop.
/ / D e c l a r e s sum and temp . I n i t i a l i z e s sum t o 0 .
i n t sum =0 , temp ;
c o u t << ” P l e a s e g i v e a number t o ad d : ” ;
/ / Us e r i n p u t s i n t o a temp o r ary v a r i a b l e t o add t o sum
c i n >> temp ;
while ( temp ! = 0 )
{
/ / S e t s sum e q u a l t o sum+temp a t s t a r t o f l o op
sum += temp ;
c o u t << e n d l << ” t o t a l : ” << sum << e n d l ;
/ / a sk s u se r t o i np ut temp v a r i a b l e a ga in
c o u t << ” Add a n o t h e r number ? I f y es , i n p u t ”
<< ” a n o nz e r o i n t e g e r . I f no , i n p u t 0 . ” << e n d l ;
c i n >> temp ;
}
is example shows a count-controlled while loop:
i n t c o u n t e r = 1 ;
while ( c o u n t e r ! = 1 2 )
{
c o u t << c o u n t e r << e n d l ;
c o u n t e r + + ;
}
12.5 for work or for play
Consider what we have needed for each loop we’ve covered. We’ve needed to ini-
tialize a variable that we want to check. We’ve also needed an end condition to test
that variable against. Finally, we needed a way of modifying that variable to meet
that end condition. Aer that, it’s whatever we’ve felt like puing in. With the for
loop, we put those three elements into the loop header, separated by semicolons (;).
Afor loop would would look something like this:
f o r ( I n t i a l i z a t i o n ; T e s t ; Up date )
{
something ;
something ;
/ / wh at e v e r e l s e you need
}
e for loop by its nature lends itself to being a count-controlled loop. You use
this kind of loop to count up (or down) each iteration until you get to the specified
value.
Let’s run through how a for loop should run, following the code below. As-
suming everything is correct, you would initialize the first value to something such
as an int counter that is set to 1. e TestExpression will include the
same Boolean logic you would use in while and do-while loops, so let’s just say
when counter is less than or equal to 5, the loop will terminate. Finally, let’s say
counter++ is the update expression. In each iteration (unless you also decide to
change counter from the body of the loop) you will move through this pretest
loop four times.
is code corresponds to the logic in Figure 12.3:
f o r (int c o u n t e r = 1 ; c o u n t e r <= 5 ; c o u n t e r + +)
{
c o u t << c o u n t e r << e n d l ;
}
…which produces the following output:
1
2
3
4
5
Figure 12.3: Logic of a for loop
12.6 Picking a Loop
Which loop you use is dependent on your preferences and needs. A for loop
is nice, but it’s more convenient as a count-controlled loop. If you needed to use
an event-controlled loop, you may prefer to use a while or do-while loop. A
for loop is a nice way to condense the initialization, end conditions and update
statement of the loop into one short line. When choosing between a do-while
and a while loop, you should remember that with a do-while, it will always
run at least once, while a while loop may run zero or more times.
12.7 Nested Loops
Much like if statements, loops can be nested within each other. Just remember to
practice good formaing habits to keep the code from being too confusing. Take a
look at the example below, then let’s talk our way through it.
/ / a s i n g l e day
f o r (int h ou rs = 0 ; h ou rs < 2 4 ; hou r s + +)
{
/ / a s i n g l e hour
for (i n t m in ut es = 0 ; i < 6 0 ; m in utes ++)
{
/ / a s i n g l e minute
f o r (i n t s e c o n d s = 0 ; s e c o n d s < 6 0 ; s e c o n d s + +)
{
/ / o u t pu t s t he c u r r e n t t im e
c o u t << h o ur s << ” : ” << minutes
<< ” : ” << s e c o n d s << e n d l ;
}
}
}
For those readers who concluded that this is a clock simulation, you are correct!
Our system of time is set up that we have 24 hours in a day, and each hour is a
60 minute cycle, and each minute is a 60 second cycle. e code mimics this by
advancing the seconds 60 times before advancing each minute. Aer 60 minutes, the
hour counter loop is incremented. Each time an outer loop starts another iteration,
variables inside the inner loops are reset.
12.8 Infinite Loops
Remember to have some way of advancing towards the end condition. What will
happen if you can’t reach that end condition from within the loop? Most likely an
infinite loop will occur, which is a loop that can’t stop itself. Depending on the
operation of the loop, you may not know what is happening, and the loop could
potentially cause disastrous results. Let’s look at an example of a while loop that
suffers from an infinite loop.
i n t c o u n t e r = 1 ;
while ( c o u n t e r ! = 1 2 )
{
c o u t << c o u n t e r << e n d l ;
c o u n t e r += 2 ;
}
Because counter starts with a value of 1, and adds 2 each time the loop
executes, counter will always be odd, and never equal twelve. erefore, the
loop will never end.
12.9 Review estions
1. Create a while loop that increments some integer variable xinitialized
with a value of 0 by 3 until the value of xreaches a value of 30. Make sure
you declare the variable and initialize it first!
2. Create a do-while loop that reads integer values given by the user into an
integer variable x, initialized to 0, then adds those values onto some variable
named totalVal until totalVal reaches at least 20.
3. Create a for loop that outputs your name to the screen 10 times before
exiting the loop.
4. Spot the logic error and correct it in the following code:
f o r (i n t j = 1 0 , j > 0 , j −−)
{
c o u t << j << e n d l ;
i f ( j = 1 )
{
c o u t << ”BOOM ! \ n ” ;
}
}
5. In the last question, was the loop an event-controlled loop or count-controlled
loop?
12.10 Review Answers
1.
i n t x = 0 ;
w h i l e ( x < 1 0 )
{
x ++ ;
}
2.
i n t x = 0 ;
i n t t o t a l V a l = 0 ;
do
{
c o u t << ” Type i n a number : ” ;
c i n >> x ;
t o t a l V a l += x ;
}
w h i l e ( t o t a l V a l < 2 0) ;
3.
f o r (i n t i = 0 ; i < 1 0 ; i ++)
{
c o u t << ” Your name h ere \ n ” ;
}
4.
f o r (i n t j = 1 0 ; j > 0 ; j −−)
{
c o u t << j << e n d l ;
i f ( j == 1 )
{
c o u t << ”BOOM ! \ n ” ;
}
}
5. Count-controlled
12.11 Further Reading
• http://www.cplusplus.com/doc/tutorial/control/
• http://www.cprogramming.com/tutorial/lesson3.html
• http://www.cprogramming.com/c++11/c++11-ranged-for-loop.html
Chapter 13
Arrays
An array is a series of variables that are the same of the same type (int,float,
double,char, and so on). Arrays are held in a computer’s memory in a strict
linear sequence. An array does not hold anything other than the elements of the
specified type, so there is no assigning an array of type float and hoping to store
astring there. Doing so would cause a “type mismatch error” and the program
wouldn’t compile. To create an array, the programmer types something like this:
char S c o t t [ 5 ] ;
e char is the data type for all elements in the array, Scott is the name of
the array (you can be as creative as you want with the name), and the 5 inside the
square brackets represents the size of the array. So char Scott[5] can hold 5
pieces of data that are of type char.
When trying to visualize an array, think of a rectangle split up into as many
pieces as the array has places to hold data. In Figure 13.1, the rectangle has five
spaces, each of type char awaiting some values.
In order to refer to the individual elements in an array, we start with the number
0 and count upwards. We use [0] to access the first element in the array, [1] for
the second, [2] for the third, and so on. In order to read or write certain locations
of the array, we state the name of the array and the element we want to access. It
should look like this:
S c o t t [ 3 ] = ’Q ’ ;
c o u t << S c o t t [ 3 ] ;
e diagram below depicts how the computer interprets this.
71
0 1 2 3 4
char Scott[5]
Figure 13.1: e array named Scott has five spaces for char data
Q
0 1 2 3 4
char Scott[5]
Figure 13.2: e fourth element of Scott now contains 'Q'
You can also store values inside the array ahead of time when you declare the
array. To do so, you need to enclose the values of the appropriate type in brackets
and separate the values with a comma. Below are two examples, one an array where
each element is of type char and another where each element is of type int.
char S c o t t [ 5 ] = { ’ S ’ ,’ c ’ ,’ o ’ ,’ t ’ ,’ t ’ } ;
i n t Joh n [ 5 ] = { 9 9 , 5 , 1 , 22 , 7 } ;
Note that, in the C and C++ language, arrays of characters intended to be
treated as a string must contain a special character called the null character1or
1Oen abbreviated NUL; Note that this is not the same as the NULL pointer
null terminator. e null terminator marks the end of the string. In C++, this is
represented by the special character '\0'. Because the null temrinator takes up
one element in the array, any character array that is intended to be used as a print-
able string must be declared having a size one larger than the longest string that
you expect to store. Initializing the above character array should really be done as
the following (notice that we make the array one element larger!):
char S c o t t [ 6 ] = { ’ S ’ ,’ c ’ ,’ o ’ ,’ t ’ ,’ t ’ ,’ \ 0 ’ } ;
Alternatively, you can initialize a character array with a string literal, as below.
We discuss string literals in more detail in Chapter 3.
char S c o t t [ 6 ] = ” S c o t t ” ;
It is also possible to let the computer figure out the appropriate length for an
array when the array is being initialized at the same time as when it is declared.
e below code produces an identical array as the previous example:
char S c o t t [ ] = ” S c o t t ” ;
13.1 Multi-dimensional Arrays
A two-dimensional array (some might call it a “matrix”) is the same thing as an
array, but is an “array of arrays”. Here’s a two-dimensional three-by-three array:
i n t R i ch [ 3 ] [ 3 ] ; / / 2D
Declaring arrays with more dimensions are possible with similar syntax. Here’s
a three-dimensional 10 ×10 ×10 example:
i n t Sam [ 1 0 ] [ 1 0 ] [ 1 0 ] ; / / 3D
And here is a four-dimensional 10 ×10 ×10 ×10 array. is is possible even
though it’s hard to visualize.
i n t T r a v i s [ 1 0 ] [ 1 0 ] [ 1 0 ] [ 1 0 ] ; / / 4D
A user can input values into a multi-dimensional array in a similar way as a
single-dimensional array.
described in Chapter 19.
i n t neo [ 3 ] [ 3 ] = { { 1 , 2 , 3 } , { 4 , 5 , 6 } , { 7 , 8 , 9 } } ;
c o u t << n eo [ 0 ] [ 0 ] << e n d l << e n d l ; / / f i r s t number , 1
c o u t << ” ” << neo [ 2 ] [ 2 ] ; / / l a s t number , 9
e same logic is applied for 3-dimensional and 4-dimensional arrays, but when
filling them be mindful of the order of the input so that when you want to view
certain elements in the array you are able to correctly access them.
13.2 Review estions
1. Declare an integer array named myInt with a size of 10.
2. If an array has a size of 20, how many indexes are there in the array and
what are they?
3. Declare a character array named myArray with a size of 4, and initialize
the characters in the array to 'Z','a','c', and 'h'.
4. Create a program in which an integer array named myArray is declared
with a size of 10. Use a for loop to prompt the user to store a value in every
index of the array. Aer the array is given values, output the values of the
array to the screen using a for loop. Output each value of the array on its
own line.
13.3 Review Answers
1. int myInt[10];
2. ere are 20: indexes 0 through 19.
3. char myArray[4] = 'Z', 'a', 'c', 'h';
4.
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t myArray [ 1 0 ] ;
c o u t << ” E nt er 10 i n t e g e r s , p r e s s [ ENTER] ”
<< ” a f t e r ev e ry i n t e g e r . \ n ” ;
for (i n t i = 0 ; i < 1 0 ; i ++ )
{
c i n >> myArray [ i ] ;
}
for (i n t j = 0 ; j < 1 0 ; j ++ )
{
c o u t << myArray [ j ] << e n d l ;
}
r e t u r n 0 ;
}
13.4 Further Reading
• http://www.cplusplus.com/doc/tutorial/arrays/
• http://www.cplusplus.com/forum/beginner/43663/
• http://msdn.microsoft.com/en-us/library/7wkxxx2e.aspx
• https://www.youtube.com/watch?v=SFGOAKYXfOo
Chapter 14
Blocks, Functions, and
Scope
14.1 Blocks
Since we’ve covered if statements and loops, let’s go into more detail about the
code that’s contained within them. When you need to contain multiple lines of
code, we’ve shown how to use braces. ese braces will create a new layer in the
code, and the lines within would be grouped into what is known as a compound
statement, sometimes called a block.
Take a look at the example below. ere are two blocks here: the one where x
is less than 5, and one where xis greater than 5. Notice the variables declared in
each, yand z. When these are declared, they are only usable within the blocks that
they were declared. When that block reaches its end, they are lost to the rest of the
program. is is because the scope of the variables within the blocks is limited to
those blocks. We discuss scope further at the end of this chapter.
77
i n t x ;
c i n << x ;
i f ( x < 5 )
{
i n t y ; / / D e c l a r e s y
c i n << y ; / / Us er i n p u t s t o r e d i n y
x += y ; / / S e t s y t o x + y
}
e l s e i f ( x > 5 )
{
i n t z ; / / D e c l a r e s z
c i n << z ; / / Us er i n p u t s t o r e d i n z
x−= z ; / / S e t s x t o x −z
}
c o u t >> x ;
14.2 Basic Functions in C++
14.2.1 What are functions and why do we use them?
Functions are an important part of C++ programming. Without them, programs
would be confusing and difficult to troubleshoot. When programs are wrien, they
tend to be wrien in logical chunks which we call subprograms. ese subprograms
are known as functions in C++ which, when called in a program, may execute what-
ever the programmer wants. Simply put, functions are like miniature programs that
when pieced together form the actual program that you are trying to write.
14.2.2 e parts of a basic function
Afunction declaration (sometimes known as the prototype) is normally placed
before the main() function in your code. is lets the compiler know that there
is a function that will be defined in more detail further on in your program. With
basic functions, your declarations should start with a return type such as double,
int, and so on; this is the data type your function will return.
Aer the return type, the next item that needs to be wrien is the function’s
name, which can be almost anything you want. Remember that you will be using
it again later in your code, so it makes sense to make it something short and logical
that you can remember! Now that you have your data type and your function name,
it’s time for zero or more function parameters. ese will be wrien inside paren-
theses immediately following your function’s name. Each parameter is in turn made
void myFunction (int parameter);
Function return type Function Name Parameters, with type denition
Figure 14.1: e structure of a function declaration
up of a data type and a name like a variable declaration. A comma separates func-
tion parameters and your declaration must end with a semicolon aer the closing
right parenthesis. Here is an example of a function declaration:
/ / c o s t a nd p r i c e a r e p a r a m e t e r s
double profit ( i n t cost , d o u b l e p r i c e ) ;
Using a function looks much like an abbreviated version of the function dec-
laration. A function call is responsible for telling the compiler when and how to
execute a function. Function calls are found in another function like main(). Of-
ten the user is prompted to enter necessary data with cout statements and his or
her response is collected with cin. Once this data is collected, the program holds
it until a function call is made somewhere in the code. Once the function call is
made, the compiler takes the entered data and then uses the code in the function
definition (which we will go over shortly) to operate on the parameters and return
a value. For your function call, write your function name followed by the variables
or values you want to pass in. In a functiton call, it is not necessary to speciy the
data types, as they are already understood.
Here is an example of a function call:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
/ / f u n c t i o n d e c l a r a t i o n ( p r o t o t y p e )
double profit ( i n t cost , d o u b l e p r i c e ) ;
i n t main ( )
{
d o u b l e a , b ;
i n t c ;
c o u t << ” E n t e r t h e m a n u f a c t u r i n g c o s t o f t h e i t e m : ” ;
c i n >> c ;
c o u t << ” E n t e r t h e r e t a i l p r i c e o f t h e i t e m : ” ;
c i n >> b ;
/ / f u n c t i o n c a l l to p r o f i t with c o s t = c and p r i c e = b
a = p r o f i t ( c , b ) ;
c o u t << a << e n d l ;
r e t u r n 0 ;
}
You have a declaration and a function call now. e only thing le is the code
inside the function definition—the function body is the most important part be-
cause it contains the code needed by the compiler to execute the function.
e function definition will usually have a lot more code than both the dec-
laration and the function call. As a result, the definition and body are also more
difficult to write than the declaration or call. e function definition and body is
oen placed aer your main() function. Multiple function definitions and bodies
can be placed aer your main() in no particular order, though it makes it less
confusing if you use the same order as when they were declared. Start your func-
tion definition with your function heading, which looks exactly like your function
declaration but without a semicolon. Following your heading, you need your func-
tion body. Start your function body by placing an opening le brace ({) on the
line following your heading. e code that makes up the function body follows the
brace. Aer the code in the body is finished, you end the body with a closing right
brace (}). Notice that the semicolon is not necessary either aer your heading or
aer your closing brace. e standard rules for semicolons apply within the body
of the function, though. What goes inside the function body depends completely
on what you want the function to do. You may declare variables to be used just in
your function and can leave the function using return statements at any time.
Below is an example of a function definition:
/ / f u n c t i o n d e f i n i t i o n
double profit ( i n t cost , d o u b l e p r i c e )
{
d o u b l e p ; / / tempo r a ry v a r i a b l e
p = p r i c e −c o s t ; / / c a l c u l a t e t h e p r o f i t
return p ; / / r e t u rn t he r e s u l t to t h e c a l l i n g f u n c t i o n
}
Great, now that you have a grasp of the three major parts of basic functions we
can move on to other related material!
e functions we just described are known as programmer defined func-
tions since the programmer defines these functions. ere are also predefined
functions which are available for your convenience. Predefined functions are func-
tions that are already wrien and defined. In order to use predefined functions, the
programmer needs to include the necessary library and then call the function wher-
ever they need it.
In the following example we will use the sqrt() function to calculate the
square root of the user’s input. e sqrt() function is described in more detail
in Chapter 17.
# i n c l u d e < i o s t r e a m >
# i n c l u d e <cmath >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
d o u b l e num ;
c o u t << ” P l e a s e e n t e r a number : ” ;
c i n >> num ;
c o u t << s q r t ( num ) << e n d l ;
return 0 ;
}
14.3 void Functions
void functions are functions that do not return a value. Notice that other func-
tion declarations that do return a value start with their return type such as double,
int, or the like. void functions behave the same except no value is returned. A
common application where a void function is used is printing the result of calcula-
tions to the screen. e calculations might be performed elsewhere, but the results
would be printed using the void function. Syntax for void functions works in
the same way as normal functions, but the keyword void is wrien where the
return data type would normally go. e declaration, function call and definition
for void functions will follow the same format as other functions. Note that, like
other functions, there does not necessarily need to be parameters in a void func-
tion. Here is an example of a simple void function declaration:
v o i d displayMessage () ;
Remember the definition and calling of displayMessage() would be the
same as any other function with the exception of the void return type and that
no value is returned! Here is an example of a definition, declaration, and how this
function would be called:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
v o i d displayMessage () ;
i n t main ( )
{
i n t x = 2 , y ;
y = x + 1 ;
/ / T h i s d oe s n ’ t r e t u r n a n y t h i n g
displayMessage () ;
r e t u r n 0 ;
}
v o i d displayMessage ()
{
c o u t << ” C a l c u l a t i o n s a re done ! ” << e n d l ;
}
14.4 Overloading Function Names
Overloading function names allows the same name to be used in multiple function
definitions but with different parameter listings. Function names can be reused
using this feature. Function name overloading eliminates problems associated with
having multiple names for functions with similar purposes and can make the code
both more understandable and more convenient for the programmer to write.
Below is an example of an overloaded function name. Notice that both func-
tions have the same name, but different parameter types.
i n t p l u s ( int num , int numr ) ;
f l o a t plus ( float num , f l o a t numr ) ;
Here is an example of improper function overloading. Simply changing the
return type does not work—the parameters must be different!
i n t p l u s ( int num , int numr ) ;
f l o a t plus ( i n t num , i n t numr ) ;
14.5 Scope
As we dive into more complex programs there is a need for a wide variety of vari-
ables in different locations in the code. Some of these variables are declared within
individual blocks of code, such as within loops or conditionals. Others are declared
completely outside functions. e two primary types of variables we are going to
look at here are local and global. e location of the declaration of a variable within
the code changes how that variable may be used.
Local variables are declared within a block of code. A local variable is available
to code from the point of its declaration through the end of that block of code. A
simple example is a variable declared in main():
i n t main ( )
{
i n t games ;
return 0 ;
}
e variable games is a local variable because it exists only within the local
function, main(). It cannot be used anywhere outside main() without some
additional work (such as passing it by reference to a function). Similarly, variables
declared in other functions are not available to code in main().
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
v o i d my_games ( ) ;
i n t main ( )
{
my_games ( ) ;
c o u t << g ames ; / / ERROR ! No such v a r i a b l e h er e !
r e t u r n 0 ;
}
v o i d my_games ( )
{
i n t games = 1 0 ;
c o u t << g ames ;
}
In the previous example function, my_games() is called by main() and
outputs 10. e variable games is local to that function. If games is referenced
anywhere else outside that function, the program will not compile.
An easy way to understand local variables is to compare them to your neigh-
bors. Everyone that lives on your street and around you are variables, and since
you all share the same street, they are local. e neighbors on an adjacent street
might be close to where you live, but since they do not share the same street, they
might not be considered neighbors. You can think of these neighbors on the adja-
cent street as other functions. While they might be close by, they do not share the
same street.
Global variables are quite different from local variables. Global variables can
be used by code anywhere within the program. A global variable is declared outside
of any function. Using similar code as in the example above, we make the games
variable global:
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t games ;
v o i d my_games ( ) ;
v o i d their_games () ;
i n t main ( )
{
games = 5 ;
my_games ( ) ;
t h e i r _ g a m e s ( ) ;
return 0 ;
}
v o i d my_games ( )
{
c o u t << g ames << e n d l ;
}
v o i d their_games ()
{
c o u t << g ames << e n d l ;
}
Both functions print the same variable, causing the program to produce the
following output:
5
5
To sum it up, local variables work only within the block of code that it is de-
clared. Global variables are declared outside functions, and can be used at any point
in the program.
14.6 Review estions
1. What are the three parts of a function?
2. Can a void function return a value?
3. How many functions can one program have?
4. What is the output of the following code snippet?
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
v o i d exa mple ( ) ;
i n t main ( )
{
r e t u r n 0 ;
}
v o i d exa mple ( )
{
c o u t << ” H e l l o World ” ;
}
5. Write code using at least one function that will ask the user to guess a
“magic” number (of your choice) between 1 and 100 until they get it right.
Aer a guess, the program should output whether the number they guessed
is higher or lower than the “magic” number. It should also display how many
guesses the user makes, and loop until the guess is correct.
6. Using at least one function, write code that prompts the user for a number
of miles travelled and a number of hours, then calculates the user’s speed in
miles per hour.
14.7 Review Answers
1. Return type, function name, parameter(s)
2. No
3. As many as you want
4. ere is no output
5.
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
v o i d gu e s sing_ g a me ( ) ;
i n t main ( ) {
gues s i ng_g a m e ( ) ;
}
v o i d gu e s sing_ g a me ( ) {
i n t g ue s s , c o u n t e r = 0 , number = 5 ;
b o o l foun d = f a l s e ;
do {
c o u t << ” Guess a number : \ t ” ;
c i n >> g u e s s ;
i f ( g u e s s > 1 00 or g u e s s <= 0 )
{
c o u t << ” Number i s betwe en 1 and 1 0 0 ! \ n \ n ” ;
c o u n t e r + + ;
}
e l s e i f ( g u e s s < number )
{
c o u t << ” Too low . G ue ss a g a i n . \ n \ n ” ;
c o u n t e r + + ;
}
e l s e i f ( g u e s s > number )
{
c o u t << ” Too h i gh . G ue ss a g a i n . \ n \ n ” ;
c o u n t e r + + ;
}
e l s e / / g u e s s == number
{
c o u t << ” You g ot i t ! \ n ” ;
found = t r u e ;
c o u n t e r + + ;
}
}while ( ! f o und ) ;
c o u t << ” I t t o o k you ” << c o u n t e r << ” g u e s s e s ! \ n ” ;
c o u t << ” Th anks f o r p l a y i n g ! \ n \ n ” ;
}
6.
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
d o u b l e mph ( double mi l e s , d o u b l e h o u r s ) ;
i n t main ( )
{
double m i l e s = 0 , h o ur s = 0 , m il es P er Hou r ;
c o u t << ” E nt e r t h e number o f m i l e s t r a v e l e d : ” ;
c i n >> m i l e s ;
c o u t << ” E n t e r t h e t r a v e l t i m e i n h o ur s : ” ;
c i n >> h ours ;
c o u t << ” Your s pe e d i n m i l e s p er hour : ”
<< mph ( m i le s , hou rs ) ;
r e t u r n 0 ;
}
d o u b l e mph ( double mi l e s , d o u b l e h o u r s )
{
r e t u r n m i l e s / ho u rs ;
}
14.8 Further Reading
• http://www.cplusplus.com/doc/tutorial/functions/
• http://www.cplusplus.com/doc/tutorial/functions2/
• http://www.cprogramming.com/tutorial/lesson4.html
Chapter 15
Problem Solving &
Troubleshooting
Problem solving and troubleshooting in programming is oen referred to as de-
bugging. Does your program not compile? Does it not achieve the desired effect?
Debugging is your answer. And, unless you are a perfect programmer, you are likely
to do quite a bit of debugging. e first step to debugging is looking for common
errors.
15.1 e Compilation Error
ese errors happen when your compiler returns an error message aer you hit
compile. e messages usually tell you what is wrong, and what line the error is
on, but be sure to double-check the lines immediately before and aer the reported
error. Because the code is incorrect, the compiler can only guess at what you meant
and give you a hint.
For example, one of the most common errors a beginning programmer will en-
counter is forgeing a semicolon. In some development environments (like NetBeans
in Figure 15.1), this will cause the error to be reported not on the line with the miss-
ing semicolon, but on the following line.
89
Figure 15.1: A syntax error in the NetBeans development environ-
ment
15.2 e Logic Error
Logic errors are oen subtle, and occur aer the code compiles. When the code is
executed, however, the result is wrong. is may happen when arithmetic opera-
tors like +,-,*, and /get mixed up. Another common issue is misplacement of
parentheses, as a misplaced parenthesis can cause problems in complex expressions.
15.3 e Infinite Loop
Another specific logic error is the infinite loop. e infinite loop is a common error
that can result in your program repeating the same block of code over and over.
For an infinite loop to occur, the conditional expression of a while,for, or
do-while loop remains true. ere are many ways for this to happen, such as
accidentally using =instead of == to compare two numbers, or using the wrong
operators, like a >in the place of a <.
Figure 15.2: An infinite loop in the NetBeans development environ-
ment
15.4 Review estions
1. Consider the following function:
d o u b l e a v e r a g e ( double s1 , double s2 , d o u b l e s3 , s4 ) ;
{
r e t un s 1 + s 2 + s3 + s 4 / 4
}
(a) Find the syntax errors in the function.
(b) ere is a logic error in the function. What is it? How does it affect
the output of the code?
2. e below program compiles, but does not get the result the programmer
wanted. Why?
i n t main ( )
{
i n t s h o t s , g o a l s , s a v e s ;
double save_perc ;
char c o n t ;
c out . u n s e t f ( i o s : : f i x e d ) ;
c out . u n s e t f ( i o s : : s ho wp oi nt ) ;
c o u t << ” E n t e r t h e number o f s h o t s on g o a l : \ t ” ;
c i n >> s h o t s ;
c o u t << ” E n t e r t h e number o f g o a l s s c o r e d : \ t ” ;
c i n >> g o a l s ;
c o u t << e n d l ;
s a v e s = s h o t s −g o a l s ;
/ / Hockey sh ows s a v e % a s d e c i m a l t o t h r e e p l a c e s
s a v e _ p e r c = ( s a v e s / s h o t s ) ;
c o u t << ” I f t h e r e were ” << s h o t s << ” s h o t s and ”
<< g o a l s << ” g o a l s , ”
<< ” t he n t h e g o a l i e ’ s s a ve p e r c e n t a g e was ” ;
c o ut . s e t f ( i o s : : f i x e d ) ;
c o u t . s e t f ( i o s : : s h o w p o int ) ;
c o ut . p r e c i s i o n ( 3 ) ;
c o ut << s a v e _ p e r c << e n d l << e n d l ;
r e t u r n 0 ;
}
15.5 Review Answers
1. (a) retun should be return. ere is an extra semicolon at the end
of the function header, and one missing aer the return statement.
(b) ere are no parentheses around the addition, so s4 will be divided
by 4, then added to s1 + s2 + s3, instead of adding all four
variables and then dividing the sum by 4.
2. Remove the unused variable cont and cout.unsetf lines. Because
shots and goals are both integers, the program does the math as though
you are looking for an int result and doesn’t store the fractional parts,
even though it stores the result in a double. Change shots,goals,
and saves to be of type double and the program will work as intended.
Chapter 16
e Preprocessor
Preprocessor directives are lines of code that are executed before the compilation of
the code begins. ese directives are like geing everyone in a room before starting
a project or doing warmups before running a race. One of the most frequently-used
preprocessor directives is #include.
When we want to include in our code a system library or some other file, we
use the keyword #include followed by the library name or the file name. e
way we distinguish between including libraries and including files is with angle
brackets and quotes, respectively. For example, when we want to use objects like
cout or cin, we need to include the iostream library like so:
# i n c l u d e < i o s t r e a m >
If we want to include a file, such as a file named myFile.h, we can write:
# i n c l u d e ” myF il e . h ”
However, when we include files, they must be in the same directory as the
file where the #include appears. We discuss the Standard Template Library in
Chapter 23, and include a short sample of other libraries in Table 16.1.
93
Library Provides Some common uses
<iostream> Input/output
stream objects
cout,cin:
see Chapters 6 and 5
<cstdlib> e C standard
library
rand(),abs(),NULL
<cmath> Mathematical
functions
pow(),sqrt(),
cos(),tan(),sin():
see Chapter 17
<iomanip> Input/output
manipulation
set_iosflags(),
setfill(),
setprecision()
<ctime> Time-related
functions
clock(),time()
<string> e string
class
See Chapter 11
<fstream> File input and
output streams
See Chapter 18
Table 16.1: Some useful libraries and a sampling of what they provide
16.1 Review estions
1. Which of the following demonstrate correct syntax for #include state-
ments? (Note: some of these may be syntactically correct but not do what
you would expect!)
(a) #include <aFile.txt>
(b) #include <iostream>;
(c) include <iostream>
(d) #include myFile.txt;
(e) #include "myFile.txt"
() #include <cmath>;
(g) include <cmath>
(h) include "cmath"
(i) #include <cmath>
(j) #include (iostream);
(k) #include <iostream>
2. Identify the the preprocessor statements in the following code:
# i n c l u d e <cstdlib >
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( i n t argc , c h ar * a r gv [ ] )
{
c o u t << ” I n c l u d e d ! ” << e n d l ;
r e t u r n 0 ;
}
3. Which library is required to use the cout object?
4. Is using namespace std; a preprocessor directive?
5. If you want to be able to use the funtion pow(), which library do you need?
16.2 Review Answers
1. a,e,i, and k.
2. e first two lines are preprocessor directives.
3. e iostream library.
4. No.
5. e cmath library.
Chapter 17
Advanced Arithmetic
Advanced arithmetic in C++ includes mathematics that can’t be used in code with-
out the use of the <cmath> library. is is mathematics that goes above and
beyond the primitive operations: addition (+), subtraction (-), multiplication (*),
and division (/). As we have seen before, some simple arithmetic might look like:
i n t x ;
x = 1 ;
x += 5 ;
e variable xis declared as an integer. e next line sets it to one. e +=
operator adds five to x, which makes xcontain six. Doing simple operations like
these does not require any special libraries or unusual commands. Any compiler
can look at a +,-,*, or /in a line of code and know exactly what the programmer
expects to happen. Some math requires a lile extra help, though. In this case, help
is the <cmath> library.
<cmath> is a library that is needed for trigonometric, hyperbolic, exponen-
tial, logarithmic, rounding, and absolute value functions. e <cmath> library is
designed to make your life simple and to make complicated mathematics easier in
C++. Using the <cmath> library in code is as simple as including it at the top of
your source code file with the rest of your libraries. For example:
# i n c l u d e < i o s t r e a m >
# i n c l u d e <cmath >
Aer the inclusion of the <cmath> library, you can use certain mathematical
functions in your code such as pow(x, y), which raises the parameter xto the
97
power of parameter y, and sqrt(z), which returns the square root of z. In your
first few C++ programs you will probably not use the more advanced mathemati-
cal functions included in the <cmath> library, but for a full list of the functions
provided in <cmath>, refer to “Further Reading” at the end of this chapter.
17.1 Examples
17.1.1 pow()
pow is the function called when you want to raise a value or variable to a certain
power. Take a look at the code below and we’ll break it down line by line.
i n t x , y ;
x = 4 ;
y = pow ( x + 1 , 3 ) + 6 ;
First, we are declaring two variables: xand y. Aer that we set xto 4. Now
we get to a more interesting section of code. We are asking the compiler to raise
the value of xplus 1 to the power of 3, add 6, and then place the result in y. To use
the pow function, you must understand its syntax. Here is the breakdown:
pow ( s t a r t i n g v alu e , power b e i n g r a i s e d )
In pow(x + 1, 3) + 6, we are raising the starting value x+ 1 to the
power of 3. Before the power of 3 is applied, 1 is added to x. In this case it is the
simple operation of 4+1, which yields 5. Aer we get 5, we raise it to the 3rd power
to get a value of 125. Aer we reach the value of 125 we are finished with the pow
function and resume using normal operators when we add 6 to 125 resulting in the
final value of 131.
Undoubtedly there are more complicated uses of the pow function, such as
multiple uses of pow in the same line of code. You might use multiple pow opera-
tions in code that calculates the length of one side of a triangle using the Pythagorean
eorem. Look at the following code and see if you can figure out what the output
value would be:
i n t x , y , z ;
x = 3 ;
y = x + 1 ;
z = pow ( x , 2 ) + pow ( y , 2 ) ;
c o u t << z ;
If you got 25, then you have the right answer! Aer initializing the variables
xand yand seing their values (3 for xand x+1 for y), we raise each value to the
power of 2. For visual reference,
z = pow ( 3 , 2 ) + pow ( x + 1 , 2 ) ;
results in
z = 9 + 1 6 ;
z’s value is set to 25. e pow function is simple to use and can make the
program simpler from a readability standpoint.
17.1.2 sqrt()
Square roots are calculated using the sqrt function. Take a look at the example
below to see how it is called in a program:
i n t a , b ;
a = 2 5 ;
b = s q r t ( a ) ;
sqrt is simpler than pow in that it only requires one parameter. Since sqrt
returns a double, you should usually assign the result to a double variable, but
in this example, sqrt returns exactly 5, so it is implicitly converted to an int
without any issues.
ere are cases where both sqrt and pow are used in the same formula, such
as when calculating the distance between two points. When writing such code, it
is very important to keep track of the parentheses and to use correct syntax. One
such syntax mistake is made when programmers think that C++ syntax is the same
as algebraic syntax. is is not the case in C++!
i n t x = ( 5 ) ( pow ( 3 , 3 ) ) ; / / I n c o r r e c t s y n t a x !
When the compiler sees this, it doesn’t view it as multiplication, but instead as
(according to a professional), “function shenanigans.” It is important to be explicit
with mathematical symbols in C++. So instead of the incorrect code above, use:
i n t x = 5 * ( pow ( 3 , 3 ) ) ;
As an example, we will use code to compute the distance between the two
points (4,4) and (6,10) on a plane.
i n t x1 , x2 , y1 , y2 ;
f l o a t d i s t ;
x1 = 4 ;
y1 = 4 ;
x2 = 6 ;
y2 = 1 0 ;
d i s t = s q r t ( pow ( x2 −x1 , 2 ) + pow ( y2 −y1 , 2 ) ) ;
c o u t << d i s t ;
Your final answer aer the calculation is executed is roughly 6.342555. With-
out the help of the advanced arithmetic operations, geing to this result would be a
difficult, long, drawn-out process. pow and sqrt are handy functions that make
life easier, all with the help of the <cmath> library.
17.1.3 Modulo
e modulo operator (the percent sign: %) finds the remainder, or what was le over
from division. is program uses the modulo operator to find all prime numbers (all
the numbers that never have a remainder of 0 when divided by every number except
1 and itsel) that can be held by an int.
# i n c l u d e < i o s t r e a m >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t divby , r e m ai n de r ;
for (i n t t e s t = 1 ; t e s t < 2 1 4 7 4 8 3 6 4 7 ; t e s t ++)
{
bool i s p r i m e = t r u e ;
f o r ( d i v b y = 2 ; d i v b y < t e s t ; di v by ++)
{/ / S t o r e t he r em ain der o f t e s t p r i m e / d iv by
re m a i nd e r = t e s t % di v b y ;
i f ( rem ai nd e r == 0 ) / / I f t h e number i s n ot p ri m e
{
i s p r i m e = f a l s e ;
break ;/ / L e av e t h e f o r l o o p
}
}
i f ( i s p r i m e ) / / I f i t p a s s e s t h e t e s t , i t i s p rime .
c o u t << ” ” << t e s t p r i m e ; / / P r i n t t he prime
}
r e t u r n 0 ;
}
17.2 Review estions
1. Which #include library is needed to use advance arithmetic operators?
2. Write C++ code to calculate 29.
3. Write a statement to set the value of a variable of type double to the square
root of 10001.
4. Complete the code below to find the length of the hypotenuse of a right
triangle (remember that a2+b2=c2) given the lengths of the other two
sides. What is the final output of your code?
# i n c l u d e < i o s t r e a m >
/ / Add n e c e s s a r y l i b r a r i e s h er e
u s i n g n am es pa ce s t d ;
i n t main ( )
{
double a = 3 . 0 , b = 4 . 0 ;
double c ;
/ /
/ / F i n i s h t he program . . .
/ /
c o u t << ” The h y pot e nus e o f t h e r i g h t t r i a n g l e i s ”
<< c << e n d l ;
}
17.3 Review Answers
1. #include <cmath> must be included to include advanced operators.
2. pow(2, 9)
3. double b = sqrt(10001);
4.
# i n c l u d e < i o s t r e a m >
# i n c l u d e <cmath >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
f l o a t a = 3 . 0 , b = 4 . 0 ;
double c ;
a = pow ( a , 2 ) ;
b = pow ( b , 2 ) ;
c = s q r t ( a+b ) ;
c o u t << ” The h y pot e nus e o f t h e r i g h t t r i a n g l e i s ”
<< c << e n d l ;
}
e final output of the code is:
The hypotenuse of the right triangle is 5.0
17.4 Further Reading
• http://pages.cpsc.ucalgary.ca/~jacob/Courses/Fall00/CPSC231/Slides/08-Arithmetic.
pdf
• http://www.cplusplus.com/reference/cmath/
Chapter 18
File I/O
File I/O refers to the input and output (I/O) from and to files. So far we have been
using cin to get input from the keyboard and cout to output to the screen. Just
like output can be sent to the screen, output can be sent to a file. Input can be taken
either from a keyboard or from a file. Input and output is handled in the program
through objects called streams. is chapter will discuss how to take input from a
file and send output to the same file or a different one.
File I/O is useful because files provide a way to store data permanently. With
keyboard input and screen output, the data is temporary and goes away once the
program is finished. When it comes to files, the data is there for us and we do not
have to waste our time typing it over and over again.
18.1 I/O Streams
If data is flowing into your program it is called an input stream. If data is flowing
out of the program it is called an output stream. We have actually been using both
types of streams already! cin, which handles a flow of data from the keyboard, is
an input stream and cout, which produces a flow of data to the screen, is an output
stream. If an input stream object is connected to a file, then the program can get its
input from that file. Similarly, an output stream object can send data to the screen
or to a file. A file can be opened for both reading and writing, in which case it can
be accessed by both input and output streams.
103
18.2 File I/O
When the program opens a file for input, the program is reading from the file. When
the program opens a file for output, the program is writing to the file. C++ provides
us with the ifstream,ofstream, and fstream classes for reading from and
writing to files. All of these classes are available through the fstream library,
which means we must #include it in our code in order to use them:
# i n c l u d e <fstream >
e ofstream type (read that as “output file stream”) is used to write data
to files. e ifstream type (“input file stream”) is used to read data from files.
Objects of type fstream (“file stream”) can combine the behavior of ifstream
and ofstream and allow us to both read from and write to files.
e cin and cout objects are already declared for you. However, in order
to use ifstream,ofstream and fstream objects, you must declare one like
you would any other variable. Declaring these objects looks like this:
/ / D e c l a re s a v a r i a b l e of ty pe i f s t r e a m named i np u t
i f s t r e a m i n F i l e ;
/ / D e c l a r e s a v a r i a b l e o f t y pe o f s t r e a m named o u t pu t
o f s t r e a m o u t F i l e ;
e variable inFile will deal with geing input from a file, while the variable
outFile will deal with outpuing data to a file.
Every file on a computer has its own name and a location (or path). An example
of a text file name is TextFile.txt and its location in a Windows operating
system might be c:\storage\TextFile.txt. In a UNIX-based operating
system, the same file might be in /home/user1/TextFile.txt. Regardless
of the operating system, we need to know the file’s path in order to tell the program
where to find the file.
18.3 Opening and closing a File
Before we can even start reading from and writing to a file we must open it. In order
to open a file you must first make an object of type ifstream,ofstream, or
fstream just like we did earlier. We open a file using a member function named
open. e ofstream object will create a file for you if the file you’re opening
for output does not exist. Otherwise, if the file already exists, the open function
will erase existing data in the file by default. e following example demonstrates
how to open files for both input and output:
# i n c l u d e < i o s t r e a m > / / F o r c i n and c o u t
# i n c l u d e <fstream > / / For i f s t r e a m and o f s t r e a m
u s i n g n am es pa ce s t d ;
i n t main ( )
{
/ / D e c l a r e s a v a r i a b l e o f t ype i f s t r e a m c a l l e d i n F i l e
i f s t r e a m i n F i l e ;
/ / D e c l a r e s a v a r i a b l e o f t y pe o f s t r e a m c a l l e d o u t F i l e
o f s t r e a m o u t F i l e ;
/ / Opens t e x t f i l e f o r i n p u t
i n F i l e . open ( ” T e x t F i l e . t x t ” ) ;
/ / C r e a t e s t e x t f i l e f o r o u t p u t
o u t F i l e . open ( ” O u t p u t T e x t F i l e . t x t ” ) ;
return 0 ;
}
Once you are done with the file, it is good practice to close it. Closing the file
disconnects it from the program and prevents the program from continuing to read
from or write to the file. If the program ends normally or crashes, the files will be
automatically closed. Closing files is even simpler than opening them. All you need
to do is use the close function with empty parentheses. For example, to close
both inFile and outFile:
i n F i l e . c l o s e ( ) ;
o u t F i l e . c l o s e ( ) ;
18.4 Reading from a File
We use the ifstream class to read data from a file. Instead of having a user input
data from the keyboard, we now input the data from a file. As you recall from earlier
in the book, we used cin with >>, the extraction operator. is is the operator
we use when we would like get input from the keyboard and it is also used with
ifstream objects. Once we have declared our variable of type ifstream and
opened a file, we can use it to input data. Using this is very similar to cin except
we replace cin with the name of our variable. For example:
# i n c l u d e < i o s t r e a m >
# i n c l u d e <fstream >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
i n t number = 5 ;
i f s t r e a m i n F i l e ;
i n F i l e . open ( ” T e x t F i l e . t x t ” ) ;
i n F i l e >> number ;
/ / The v al u e 5 i n number i s o v e r w r i t t e n
/ / by t h e i n t e g e r s t or e d i n t h e f i l e
r e t u r n 0 ;
}
is will read in one integer from the file and store it into the variable num-
ber. You can input all different types of data including characters, doubles, and
floats. Overall, ifstream objects are very similar to cin—you just have to
declare one and remember to use the variable name instead of cin.
18.5 Writing data to a File
We use the ofstream class to output data to files. cout outputs data to our
screen whereas ofstream stores data in files. Just like cout,ofstream ob-
jects use <<, the insertion operator. Using this is very similar to cout except we
replace the cout with the name of our variable. For example:
# i n c l u d e < i o s t r e a m >
# i n c l u d e <fstream >
u s i n g n am es pa ce s t d ;
i n t main ( )
{
ch ar L e t t e r = ’A ’ ;
o f s t r e a m o u t F i l e ;
o u t F i l e . open ( ” O u t p u t T e x t F i l e . t x t ” ) ;
o u t F i l e << L e t t e r ; / / P u t s t h e l e t t e r ’A ’ i n t o t h e f i l e
return 0 ;
}
is example would write the leer 'A' to the text file we created named
OutputTextFile.txt. You can also create numeric variables and output them
to the file just like:
i n t num = 1 0 ;
o u t F i l e << num << e nd l ;
is example would output the number 10 and create a new line in the text file
we created.
18.6 Introduction to Classes and Objects
We will go into more detail about classes and objects in Chapter 21 but it is nec-
essary to go over it briefly in this section. Both cin and cout are objects. An
object is a variable that has functions built in and may have multiple pieces of data
associated with it. ifstream and ofstream are object types that define which
operations may be performed on and which data are stored in the objects. For exam-
ple, the function open() (along with close() and many others) is considered a
member function of ifstream and ofstream, which means it is a function
that is associated with object of those two types. Geing a lile more into detail,
these object types are defined as part of a class. A class is a blueprint for complex
data types. We already know data types such as integers, doubles, and chars,
but using classes, you will be able to design your own data type.
When calling the functions open or close, you will notice we use a period
between the object name and the function. We call this the dot operator and it is
used to reference member functions and member variables of a class.
18.7 Other functions
e <fstream> library comes with many functions to help test to see if things are
working. One example is the fail() function. We use this function to determine
whether the file was opened successfully or not. We usually use if statements with
the function so that if the file does not open correctly we can warn the user. For
example:
i n F i l e . open ( ” T e x t F i l e . t x t ” ) ;
i f ( i n F i l e . f a i l ( ) )
{
c o u t << ” F a i l e d t o open ! ” ;
}
is will warn the user if the file did not open correctly. If the file did open
correctly, the program would continue without printing the error message.
e next function is the eof() (end offile) function. is function tests to
see if the stream has reached the end of the file. is function is very useful in order
to know when to stop reading from the file. For example:
i n t number ;
i n F i l e . open ( ” T e x t F i l e . t x t ” ) ;
while ( ! i n F i l e . e of ( ) )
{
i n F i l e >> number
}
is example shows how the eof() function can be used in a while loop.
e while loop will read integers from the file until the program reaches the end
of the file. is is useful for gathering all the data from one file.
e get() and put() functions are used to read and write single characters,
respectively. e function get() allows the program to read in a single character
into a variable of type char. When we use the >> operator, spaces, tabs and new-
lines—the whitespace characters—around data are skipped automatically. However
with get(), nothing is done automatically, so the whitespace characters can be
extracted, too. e member function get() takes one argument in parentheses
that must be a char variable. For example:
char C h a r a c t e r ;
i f s t r e a m i n F i l e ;
c i n . g e t ( C h a r a c t e r ) ;
/ / or
i n F i l e . g e t ( C h a r a c t e r ) ;
is will read in the next character typed on the keyboard or from the file. Even
if the next character is a space, tab, or newline, the program will store that character
in the variable.
e put() function is used to output one character. is function takes one
argument of type char in the parentheses. For example:
char C h a r a c t e r = ’ \ n ’ ;/ / ne w line c h a r a c t e r
o f s t r e a m o u t F i l e ;
c o ut . p ut ( C h a r a c t e r ) ;
/ / o r
o u t F i l e . p ut ( C h a r a c t e r ) ;
18.8 Review estions
1. What do we call the type of object used to control data flowing into your
program?
2. What do we call the type of object used to control data flowing out of your
program?
3. What header file must you #include in order to use ifstream and
ofstream?
4. What are ifstream and ofstream used for?
5. How do you declare an ifstream object named input and an of-
stream object named output?
6. How would you open a file named TextFile.txt with an ifstream
object called input?
7. How would you close a file named TextFile.txt with an ofstream
object called output?
8. What kind of function is the eof() function and what does it do?
9. What are the benefits of using files for input and output?
10. What is the difference between cin >> c; and cin.get(c); if cis
of type char?
11. Write a program that outputs the contents of some file to the screen.
12. Write a program that reads in a text file and prints to the screen the number
of times the character 'e' shows up.
18.9 Review Answers
1. An input stream
2. An output stream
3. You need to #include <fstream>
4. ifstream is used to read data from a file. ofstream is used to write
data to a file.
5. ifstream input;
ofstream output;
6. input.open("TextFile.txt");
7. output.close();
8. e eof() function is a member function. It returns true if the program
has reached the end of the file.
9. File input and output are useful because files provide a way to store data
permanently. With keyboard input and screen output, the data is temporary
and disappears once the program is finished. e data stored in files on the
other hand remains the same until another program changes it. Also, an
input file can be used by many programs at the same time without having
to store multiple copies or re-enter the data over and over again.
10. e first cin statement the next non-whitespace character into c, but the
call to cin.get() stores the next character in cwhether it is whitespace
or not.
18.10 Further Reading
• http://www.cprogramming.com/tutorial/lesson10.html
• http://www.cplusplus.com/doc/tutorial/files/
• http://www.tutorialspoint.com/cplusplus/cpp_files_streams.htm
Chapter 19
Pointers
Pointers do just what they sound like they do. ey point to a space in memory,
usually a location occupied by a variable. A pointer is an address in memory. e
pointer itself is a variable, but it also refers to a variable. It is declared using an
asterisk following the data type:
i n t * p t r ;
e variable named ptr is of type int*, an “integer pointer” that stores the
address of a variable of type int.
To indicate that a pointer variable is not pointing toward any usable data,
we oen set its value to NULL, which is defined as zero when you #include
<cstdlib>:
i n t * p t r = NULL ;
C++11 provides a dedicated null pointer object called nullptr that can be
used similarly:
i n t * p tr = n u l l p t r ;
ere are two operators used in conjunction with pointers. e *operator,
beyond being used for multiplication and for pointer declarations, also acts as the
dereference operator. e dereference operator changes the pointer into the value
it is pointing to. It “follows” the address stored in the pointer and returns whatever
is in that location.
e &operator is the reference operator. e dereference operator returns
the memory address of the variable it precedes. You will use this to produce a pointer
111
Figure 19.1: e state of the variables aer lines 1-3
to the indicated variable. Let’s declare pointer pand use it:
i n t * p ; / / D e c l a r e an i n t p o i n t e r
i n t v a r 1 = 2 ; / / D e c l a r e an i n t , s e t i t t o 2
p = &v a r 1 ; / / Take t h e a d d r e s s of v a r1 and s t o r e i t i n p
c o u t << * p ; / / Go t o t h e a d d r e s s s t o r e d i n p ;
/ / r e t u r n t h e v a l u e ; p r i n t i t o ut
e output of this code is:
2
Here is a slightly longer example:
i n t * p ;
i n t v a r 1 = 2 ;
i n t v a r 2 = 4 ;
p = &v a r 1 ; / / Take t he a d d r e s s o f v ar 1 and s t o r e i t i n p
* p = v a r 2 ; / / Go t o t he a d d re s s s t o r e d i n p ;
/ / a s s i g n i t t h e v a lu e s t o r e d i n v a r2
/ / The p r ec e di ng two l i n e s a re e q u i v a l e n t to v ar 1 = v a r2
c o u t << * p << e n d l ;
c o u t << v a r 1 << e n d l ;
c o u t << v a r 2 << e n d l ;
e output of this code is:
4
4
4
Figure 19.1 shows the state of the variables in the second example aer they
are declared and initialized (lines 1-3). Aer the fourth line is executed, pwill store
the address of var1. Figure 19.2 shows the state of the variables. Aer the fih
line of code is executed, the location where ppoints is assigned the value stored in
var2. Since pcontains the address of var1,var1 receives that value. Figure
Figure 19.2: e state of the variables aer line 4
Figure 19.3: e state of the variables aer line 5
19.3 shows the state of the variables.
Use caution when declaring pointers. If you are declaring more than one pointer
in a single line, make sure to indicate each pointer variable with the *before the
variable name. Here is a correct declaration of two pointers:
i n t * p , * q ;
is results in an integer pointer named pand an integer pointer named q.
Contrast that with the below code:
i n t * p , q ;
is results in an integer pointer named pand an integer named q. An equiv-
alent way to write the above is:
i n t q , * p ;
19.1 Review estions
1. What is the output of the following code?
i n t * a , b , c ;
a = &b ;
b = 5 ;
c = 1 ;
b=b−b ;
c = b * b ;
* a = c −* a ;
a = &c ;
* a = c −7 ;
c = c + c ;
* a = * a + b ;
c = c + b ;
b = c −3 ;
c = * a −7 ;
c o u t << * a << e n d l ;
c o u t << b << e n d l ;
c o u t << c << e n d l ;
2. What is the output of the following code?
i n t a , b , * c ;
a = 7 ;
b = 4 ;
c = &a ;
a = * c −a ;
* c = * c + 4 ;
a = b + a ;
c = &b ;
a = a −b ;
* c = b + a ;
* c = * c −1 ;
a = a * 1 ;
a = b −* c ;
a = a −* c ;
c o u t << a << e n d l ;
c o u t << b << e n d l ;
c o u t << * c << e n d l ;
19.2 Review Answers
1. -21
-17
-21
2. -7
7
7
Chapter 20
Dynamic Data
Up to this point, we have only discussed variables that are set up at compile time.
Allocating space for variables at compile time is adequate in many cases, but occa-
sionally a program will need to allocate space for data in memory while it is running.
Consider the following code:
i n t arraySize ;
c o u t << ” E n t e r t h e number o f e l e m e n t s i n y ou r a r r a y : ” ;
cin >> arraySize ;
/ / We want t o c r e a t e an a rr a y with a r r a y S i z e e le me nts
i n t myArray [ a r r a y S i z e ] ; / / SYNTAX ERROR !
In order to allocate the space for myArray, the compiler needs to know how
many elements make up the array so that there is enough room in memory to ac-
commodate the array. Unfortunately, the value of arraySize is not known until
the user enters something on the keyboard aer the program has started running and
as a result, the compiler returns a syntax error.
In C++, pointers are used to keep track of dynamically-allocated data:
f l o a t * f P t r = NULL ; / / ( 1 ) D e c l a r e a p o i n t e r t o a f l o a t ,
/ / which c u r r e n t l y p o i n ts nowhere
In order to dynamically allocate an object of type float, we use the new
operator:
fPtr = new f l o a t ;/ / ( 2 )
e created object of type float does not have a name, so the new operator
117
NULL
float*
fPtr
float*
fPtr
float
float*
fPtr
2.2
float
(1)
(2)
(3)
Figure 20.1: Allocation and dereferencing of pointers
returns a float* that can be used to access the object. is pointer is stored in
fPtr. We use the dereference operator (*, that is) to access the data:
* f P t r = 2 . 2 ; / / ( 3 ) Goes t o a d d r e s s a t f P t r & p u ts 2 . 2 t h e r e
c o u t << ” D ata a t ” << f P t r << ” : ” << * f P t r << e n d l ;
/ / Th i s o u t p u t s : D ata a t 0 x 2 00 10 2b 0 : 2 . 2
/ / Note t h a t t he a d d r e s s l i s t e d may d i f f e r
/ / Also n o te t h e d i f f e r e n c e betwe en p r i n t i n g f P t r and * f P t r
Notice that when a value is assigned to fPtr, the pointer is being changed.
When a value is assigned to *fPtr (notice the dereference operator), the floating-
point value at the address stored in fPtr is changed.
float*
fPtr
2.2
float
(4)
float
Memory leak
float*
fPtr
2.2
float
(5)
3.3
float
Memory leak
Figure 20.2: Allocation and memory leaks
f l o a t * f P t r ;
fPtr = new f l o a t ;
* f P t r = 2 . 2 ; / / Goes t o a d d r e s s a t f P t r & p u t s 2 . 2 t h e r e
c o u t << ” D ata a t ” << f P t r << ” : ” << * f P t r << e n d l ;
fPtr = new f l o a t ;/ / ( 4 ) f P t r now h o l d s a d d r e s s o f
/ / a new f l o a t o b j e c t
* f P t r = 3 . 3 ; // (5)
c o u t << ” D ata now a t ” << f P t r << ” : ” << * f P t r << e n d l ;
/ / Th is o u t p u t s :
/ / Data a t 0 x 20 01 0 2b 0 : 2 . 2
/ / D at a now a t 0 x 2 0 0 4 8 3 c 0 : 3 . 3
In this example, the float containing the value 2.2still resides in memory,
but is no longer reachable. is condition is called a memory leak, and results in
programs that consume more memory than they require. In order to free up the
memory properly, we use the delete operator:
f l o a t * f P t r ;
fPtr = new f l o a t ;
* f P t r = 2 . 2 ; / / ( 6 ) Goes t o t h e a d d r e s s a t f P t r and s t o r e s
2 . 2 t h e r e
c o u t << ” D ata a t ” << f P t r << ” : ” << * f P t r << e n d l ;
d e l e t e f P t r ; / / ( 7 ) F r e e s up t h e d y n a m i c a l l y −allocated
/ / memory a t t he a d d r e s s s t o r e d i n f P t r
At this point in the code, fPtr can be referred to as a dangling pointer, since
the memory location it refers to is no longer valid, and the pointer just “dangles”
there, pointing to nothing useful.
float*
fPtr
2.2
float
(6)
float*
fPtr
dangling
pointer
(7)
Figure 20.3: Deallocation and dangling pointers
Arrays can be dynamically allocated, too:
f l o a t * f P t r = new f l o a t [10]; / / A l l o c a t e an a rr a y o f t en
/ / f l o a t s and s t o r e t h e i r l o c a t i o n i n f P t r
Arrays must be deleted in a similar fashion, but the syntax changes slightly:
d e l e t e [ ] f P t r ; / / F r e e up t h e e n t i r e a r r a y
20.1 Review estions
1. Write code to declare an integer pointer and dynamically allocate an integer.
On the next line, assign this dynamically-allocated integer the value 13.
2. Given the following code, write a few lines that deallocate any dynamically-
allocated memory and set all pointer values to NULL:
i n t * a = new i n t [24];
i n t * b ;
i n t c ;
b = &c ;
20.2 Review Answers
1.
i n t * i P t r = new i n t ;
* i P t r = 1 3 ;
2.
d e l e t e [ ] a ;
a = NULL ;
b = NULL ;
20.3 Further Reading
• http://www.cplusplus.com/doc/tutorial/dynamic/
Chapter 21
Classes and Abstraction
Imagine for a second you’re behind the wheel of an automobile. You’re driving
along, but do you know your engine is working right if it’s not making any horren-
dous screeching sounds? Do you have any idea how your steering actually works
when you turn the wheel? So long as you can press down on the accelerator to
move forward and the steering handles correctly, you probably don’t care about the
specifics of how things work.
Abstract data types (ADTs) are the automobiles of C++, and one of the rea-
sons C++ is known as an object-oriented programming language. It’s their job
to package and obscure the information from the average user, and at the same time
make their lives more convenient. ADTs can be thought of as a group of data of dif-
ferent types that are treated as a single item. For example, if we wanted to record
the name, identification number, age, graduation date, and sex of all of the students
on a campus, we could create a new data type named Student with those vari-
ables. In the following sections we will show you how to use and define two types
of ADTs: structures and classes.
21.1 structs
A common example of a struct is a Point.Points store int,float, or
double variables xand y, which represent the position of the Point on the the
123
X and Y axes on a coordinate plane. Such a struct might look like this:
struct P o i n t
{
d o u b l e x ;
d o u b l e y ;
} ;
In the example, the keyword struct is used to declare the structure definition
while the identifier, the word directly to the right of struct (Point), is the structure
name and the name of a new data type. e braces are used just like when we define
a function. However, directly aer the closing brace, there must be a semicolon!
Once a structure is defined, it can be used just like the data types int,char,
string, and so on. For example, we might declare a Point structure named
input like this:
Point input ;
21.2 Assigning values to member variables
Any variable of type Point such as the one above is a collection of two variables,
xand y. Any variables contained in the struct can be accessed by combining
the structure name—input in our example—followed by a symbol called the dot
operator (the period, .) and the member variable’s name. For example, if we
wanted to set xin input, we would use the dot operator as follows:
i n p u t . x = 5 ;
21.3 Classes
classes are like structs except classes contain both variables and functions,
whereas structs only contain variables.1Also, in a struct, member variables
are public by default while all members of a class are private by default. We’ll
discuss the distinction more in a minute. First, let’s take a look at an actual class
definition.
1is has been the conventional way to think about classes and structs,
but in reality the only difference between the two is that members of a struct
are public by default and members of a class are private by default.
c l a s s Rectangle
{
p u b l i c :
Rectangle () ; / / A d e f a u l t c o n s t r u c t o r
/ / The f o l l o w i n g two l i n e s a r e m u t a t o r s
v o i d s e t B a s e ( float l e n g t h ) ;
v o i d s e t H e i g h t ( f l o a t l e n g t h ) ;
/ / The f o l l o w i n g two l i n e s a r e a c c e s s o r s
float g e t H e i g h t ( ) ;
float g e t B a s e ( ) ;
/ / The f o l l o w i n g two l i n e s perfo rm o p e r a t i o n s
float f i n d A r e a ( ) ;
float findPerimeter () ;
private :
float Base ;
float Height ;
} ;
Notice the similar syntax to the struct. Like a struct, the declaration
starts with the class keyword, followed by the name of the class, and aer the
closing right brace, a semicolon. Notice the public: and private: sections
of the definition. To indicate that a set of member variables or functions is private,
we use the private keyword followed by a colon. Everything aer the keyword
will be considered private. We will discuss what this means in the next section.
On the other hand, if we want to indicate that a set a member variables or
functions is public, we use the keyword public followed by a colon. Everything
aer this keyword will be considered public.
21.4 public and private variables and
functions
e biggest difference between classes and structs is the ability to determine
how accessible the data within the class is. A general rule of thumb is to put vari-
ables in the private: section, where they would be referred to as private mem-
ber variables, and related functions in the public: section, where they would
be referred to as public member functions. Private members can only be accessed
by the class’s member functions and nowhere else, while public members can be
used anywhere, in the same way that the members of a struct can be used.
Within the above class definition, we have seven member functions that we
need to define. Each function has a specific purpose to set the values of private
member variables, return the values of private member variables, or perform some
other operation using those member variables.
Functions that are declared in the above code with names starting with the
word get will be used to access the variables; these functions are called accessors.
Functions that are declared in the above code that have names starting with the
word set will be used to change the variables’ values; these functions are called
mutators. Accessors and mutators can be named whatever you like, but it is a
common convention to name them get and set plus the name of the variable you
are accessing or mutating.
e functions whose names start with find perform operations using the vari-
ables, but do not change them or return their values directly. e function named
Rectangle() is known as a constructor. When a Rectangle object is cre-
ated, it will be initialized according to the code in this constructor. By the end of this
chapter, you’ll understand how useful these are in object-oriented programming.
21.5 Defining member functions
We now describe how to use member functions with private member variables.
When we define a member function, all the member variables within the class
are accessible to the function. For example, we can define the member function
setBase() from Rectangle above like this:
v o i d R e c t a n g l e : : s e t B a s e ( float length )
{
Base = l e n g t h ;
}
In this code, we are able to directly access the member variable Base because
both the function setBase() and the member variable Base are a part of the
class. Since we are not returning anything to the user, the function is defined as
avoid function. In order to define a member function, we have to use a special
operator called the scope resolution operator (::). e function is defined by
using the return type, the class name, scope resolution operator, then the member
function name with any parameters listed just like any other non-class function.
21.6 Using member functions
All member functions have direct access to member variables even if the variable
is private. e reason we use mutators is because we do not want the user to have
direct access to any variables within the class—we give them indirect access instead.
We do this by requiring them to pass a value to the mutator member function which
sets the member variable. at might look like this:
i n t main ( )
{
Rectangle r ;
float b ;
c o u t << ” P l e a s e i n p ut t he l e n g t h o f t h e b a s e : ” ;
c i n >> b ;
r . s e t B a s e ( b ) ;
return 0 ;
}
In the above code, we start by creating a Rectangle variable named r. Aer
the user is prompted for the length of the base, which is stored in the variable b,
we call the setBase() member function with the dot operator and pass bas a
parameter to the function.
We are able to pass the value of the variable entered by the user to the setBase()
function which then sets the member variable Base to the passed value. is is how
we “mutate” private member variables in a class using a public member function.
To retrieve the value of a member variable, we need to create accessor func-
tions. ese are defined like this:
f l o a t R e c t a n g l e : : g e t B a s e ( )
{
return Base ;
}
When it comes to using accessors, it is very simple. Just match the data type
that you want to access, in this case it was a float, and define the member function
with that return type. en, in order to access the variable, all we need to do is
use the keyword return followed by the identifier. is enables us to access the
private variable when we need to.
21.7 classes and structs together
We can also combine structs and classes if need be. For example, if we wanted
to take in three points we could create a Triangle class with these points which
are individually of type Point, a struct that contains xand yvariables:
struct P o i n t
{
d o u b l e x ;
d o u b l e y ;
} ;
c l a s s Triangle
{
p u b l i c :
/ / a c c e s s o r s f o r p o i n t s a , b , and c
/ / m u t a t o r s f o r p o i n t s a , b , an d c
private :
P o i n t a ;
P o i n t b ;
P o i n t c ;
} ;
Here we have the ability to combine a struct with a class in order to have
all three points, a,b, and cthat each contain their own variables xand y. Despite
the fact that the variables in the struct are public, we cannot access those specific
values outside the Triangle unless we use a member function. is is because
they’re still private members of the class Triangle, so their scope is limited to
functions within the class. If we had a mutator function for Point a, it might
look like this:
v o i d T r i a n g l e : : s et A ( d o u b l e userX , double user Y )
{
a . x = userX ;
a . y = u se r Y ;
}
e values of userX and userY are passed in by the calling function. Notice
again that in order to access the xand ycoordinates, we must use the dot operator
with any of the Point objects a,b, or c.
21.8 Constructors
Another way to set the values of the variables in a class is through constructors. A
constructor is a member function with the same name as the class and cannot be
called directly. Constructors are what we use to initialize the variables of the class
when it’s first created. For example, if we wanted to set default values for a class
named student defined as:
c l a s s student
{
p u b l i c :
student () ; // constructor
/ / a c c e s s o r s
// mutators
private :
s t r i n g name ;
i n t age ;
i n t grad_year ;
s t r i n g i d ;
} ;
we would have a default constructor with the name student() without any re-
turn type. To initialize the variables in the class through the constructor, we use
syntax similar to a function definition:
student :: student ()
{
name = ”N/A” ;
age = 0 ;
g r a d _ y e a r = 0 ;
i d = ” A 0000000 0 ” ;
}
21.9 Overloading Member Functions
Note that, like other functions, you can overload any of the functions in a class.
Going back to the Rectangle example used earlier, take a look at the following
code.
c l a s s Rectangle
{
p u b l i c :
Rectangle () ; / / A d e f a u l t c o n s t r u c t o r
/ / O verl oade d c o n s t r u c t o r
Rectangle ( f l o a t userBase , f l o a t u s e r H e i g h t ) ;
v o i d s e t B a s e ( float l e n g t h ) ; / / T he se two l i n e s a r e m u t a t o r s
v o i d s e t H e i g h t ( f l o a t l e n g t h ) ;
f l o a t g e t H e i g h t ( ) ; / / These two l i n e s a re a c c e s s o r s
f l o a t g e t B a s e ( ) ;
f l o a t f i n d A r e a ( ) ; / / T hese two l i n e s perf or m o p e r a t i o n s
f l o a t findPerimeter () ;
private :
f l o a t B a s e ;
f l o a t Height ;
} ;
Notice the second constructor, Rectangle(float userBase, float
userHeight). We define it very similarly to the default constructor:
Rectangle :: Rectangle ( f l o a t userBase , f l o a t u s e r H e i g h t )
{
B as e = u s e r B a s e ;
H ei gh t = u s e r H e i g h t ;
}
21.10 Review estions
1. Given the following struct definition and global variable:
struct personInfo
{
s t r i n g name ;
i n t b i r t h _ y e a r ;
i n t b ir t h_ m o n th ;
i n t b i r t h _ d a y ;
i n t age ;
} ;
personInfo pinfo ;
which of the following are incorrect ways to use the dot operator?
(a) pinfo.age
(b) personInfo.birth_year
(c) information.name
(d) pinfo.(string name)
(e) birth_year.pinfo
2. Create a class called Animal that can store information about animals
in a zoo and has the following private variables:
s t r i n g name ; / / t h e name o f t h e a n i m a l
i n t pounds ; / / number o f p oun ds o f f o od e a t e n
ch ar animalType ; / / t h e t y p e o f a n i m al :
/ / ’ h ’ f o r h e r b i v o r e
/ / ’ c ’ f o r c a r n i v o r e
You should have public member functions that get and set each variable, and
a function called print() that prints all the information about the animal.
3. is program will require a struct and a class.
Write a program that can calculate the slope of a line.
You will have a struct called Point which contain the following vari-
ables:
d o u b l e x , y ;
You will then have a class called Line, and it will have the following private
variables:
P o i n t a , b ;
Your class should have accessor and mutator functions, a function that calcu-
lates and returns the slope of a line between the two Points as a double,
and a function that outputs the data to the user called print().
21.11 Review Answers
1. Only (a) is correct: (b) through (e) will result in syntax errors.
2.
c l a s s Animal
{
public :
Animal ( ) ;
s t r i n g getName ( ) ;
void setName ( s t r i n g inputName ) ;
i n t g e t Pou n d s ( ) ;
void setPounds ( int inputPounds ) ;
char getType ( ) ;
void setType ( ch ar i n p ut T y pe ) ;
void p r i n t ( ) ;
private :
s t r i n g name ; / / t h e name o f t h e a n i m al
i n t pounds ; / / number o f p ound s o f f o od e a t e n
char animalType ; / / t h e t y p e o f a n i m a l
} ;
21.12 Further Reading
• http://pages.cpsc.ucalgary.ca/~jacob/Courses/Fall00/CPSC231/Slides/08-Arithmetic.
pdf
• http://www.tutorialspoint.com/cplusplus/cpp_classes_objects.htm
• http://www.cprogramming.com/tutorial/lesson7.html
Chapter 22
Separate Compilation
Separate compilation is the process of breaking a C++ program into separate files
to improve organization. Parts of the program can be spread out over a number
of different files that are later compiled individually, then linked using a linker
to produce the final, working program. When changes are made, only those files
with changes need to be recompiled, the result of which can then be relinked with
the previously-compiled files. is process is nearly invisible in most development
environments, which recompile and relink these files automatically. When the de-
velopment environment takes care of these details, the user is le with the sole task
of making changes where they are needed.
One of the most basic applications of separate compilation is used when writing
abstract data types. Recall from Chapter 21 that there are declaration and definition
sections in a class. e declaration contains class functions and variables, both
public and private, while the definition section is where the function definitions and
most actual code can be found. e process of separate compilation requires the
two sections to be split into separate files, each of which is wrien and maintained
separately and later used together to create a working program.
Declarations will be put into the interface file or the header file which typ-
ically has a .h suffix. In most code wrien by novice programmers, there will be
only one class declaration in each header file. To use the class in your code
elsewhere, you should use #include followed by the file name in double quotes.
Below is an example of the contents of an interface file called student.h.
133
# i n c l u d e <string >
u s i n g n am es pa ce s t d ;
c l a s s student
{
p u b l i c :
student () ;
i n t getA ge ( ) ;
v o i d setAge ( i n t u p da t e ) ;
i n t g e t I D ( ) ;
v o i d s e t I D ( int u pd a te ) ;
s t r i n g getName ( ) ;
v o i d setName ( s t r i n g upd a te ) ;
private :
i n t age ;
i n t ID ;
s t r i n g name ;
} ;
To use the student class in some other source code file, that file should in-
clude the following line:
# i n c l u d e ” s t u d e n t . h ”
e quotes around student.h tell the compiler to find the header file in the
same directory as the current file.
e implementation file will include all the function definitions for the stu-
dent class. e implementation file can be called anything the programmer wants,
but typically ends with a .cpp suffix. For example, the implementation file for
student will probably be student.cpp.
To ensure that a new implementation file is compiled into your program, you
do not need to #include anything. However, the development environment will
automatically compile and link the implementation file if it has been added to your
project. e only files that you should #include are header files.
To avoid linker errors, your files should have safeguards to ensure that classes
and functions are not declared more than once within the same program. ese
safeguards are simple, and should be included in each header file. For example, we
place the following two lines at the top of the file student.h:
# i f n d e f STUDENT_H / / STUDENT_H c o u l d be a n y t h i n g
#define STUDENT_H / / a s l o n g a s i t i s unique t o t h i s f i l e
e following line should go at the end of the same file:
# e n d i f / / STUDENT_H −a r em i n de r a b ou t th e # i f n d e f above
e above three lines do the following:
1. Test if STUDENT_H has been previously #defined, usually because this
header file has been #included elsewhere.
2. If it has not been #defined, #define it now and proceed with compiling
the code between the #ifndef and #endif.
3. Close the #ifndef block. If STUDENT_H was previously defined, skip
to the line aer this one.
Here is an example of what these lines look like alongside some actual code:
# i f n d e f STUDENT_H
#define STUDENT_H
c l a s s student
{
/ / c l a s s d e c l a r a t i o n b e c a u s e t h i s i s an i n t e r f a c e f i l e
} ;
# e n d i f / / STUDENT_H
is combination of preprocessor directives will ensure that the student
class is only defined once.
22.1 Review estions
1. What is a header file?
2. What file extension do we typically use for a C++ header file?
3. What file extension do we typically use for a C++ implementation file?
4. In which file would would you typically store an abstract data type’s (ADT’s)
declaration?
5. How do you incorporate a header file named something.h into a file
named main.cpp?
6. Do you incorporate an implementation file into your project the same way?
7. How do you prevent redeclaration of ADTs and functions in header files?
22.2 Review Answers
1. A header file stores the interface of an ADT
2. A header file ends in .h
3. An implementation file ends in .cpp
4. In the interface file
5. Add #include "something.h" alongside the other #include
statements in main.cpp.
6. No, the implementation file will automatically be compiled and linked by
your development environment as long as the implementation file is in your
project.
7. You prevent redeclaration by adding lines similar to the following to the top
of your header file:
#ifndef SOMETHING_H
#define SOMETHING_H
en add the following to the end of the header file:
#endif / / SOMETHING_H
22.3 Further Reading
• http://elm.eeng.dcu.ie/~ee402/ee402notes/html/ch03s14.html
• http://web-ext.u-aizu.ac.jp/~fayolle/teaching/2012/C++/pdf/1-separate_compilation.
pdf
Chapter 23
STL
e Standard Template Library (STL) provides a set of tools beyond those that are
provided by the “base” C++ language. While a comprehensive discussion of the
features of the STL is far beyond the scope of this text, there are several libraries
that offer extremely important features with which you should become comfortable.
Note: rather than assuming that
u s i n g n am es pa ce s t d ;
is at the top of every code example, each data type, function, or variable derived
from the STL will be shown with the prefix std::. is highlights which parts of
the examples below come from the STL, and which are part of the language.
23.1 #include <utility>
#include <tuple> (C++11)
e pair class, found in <utility>, links two values which may be of different
types. e tuple class, introduced in C++11, links any number of values which
may be of different types. For example, to link a student’s identification number (an
integer) and their grade point average (a float), we can write:
s t d : : p a i r < int ,f l o a t > g r a d e s = { 1 1 2 2 3 3 , 3 . 8 1 } ;
137
We can assign different values to the pair later with the make_pair function:
g ra d es = s t d : : m ak e_pair ( 1 2 3 4 5 0 , 2 . 7 9 ) ;
e first and second members are used to extract the individual compo-
nents of the pair:
s t d : : c o u t << ” ID : ” << g r a d e s . f i r s t << ” ( GPA ”
<< g r a d e s . s ec on d << ” ) ” << s t d : : e n d l ;
/ / Th i s p r i n t s :
/ / ID : 123 4 5 0 (GPA 2 . 7 9 )
If we wanted a more complicated set of values linked together, such as a stu-
dent’s name, identification number, grade point average, and major, we could con-
struct the following:
t up l e < s t d : : s t r i n g , int ,f l o a t , s t d : : s t r i n g > e th an =
{” E tha n A l l e n ” , 8 0 2 8 0 2 , 3 . 1 5 , ” Engineering ” } ;
Unfortunately, the tuple class does not have first or second members.
e first and second elements can be retrieved in a slightly more complicated way
than with pair objects:
s t d : : c o ut << s t d : : g et <0 > ( e t ha n ) << ” ’ s majo r i s ”
<< s t d : : g et <3 >( e tha n ) << s t d : : e n d l ;
/ / Th i s p r i n t s :
/ / E th an A l l e n ’ s m aj or i s E n g i n e e r i n g
In the code below, the get function returns a reference to the third element
(the GPA) of the tuple ethan, and sets that value to 3.99:
s t d : : get < 2 >( e tha n ) = 3 . 9 9 ;
ese types may not be all that useful by themselves, but are oen used in
conjunction with container classes like vector and map, described below.
23.2 #include <iterator>
Iterators are objects that refer to elements within a container object (like std::vector,
std::map, and std::array) and allow for traversal through those elements.
e list of features in iterators vary depending on the container class. While the
specifics of the iterators vary, most iterators belong to one of the following cate-
gories, based on the operations that may be performed on them.
23.2.1 Forward iterators
• Can be incremented to move forward in the container to the next item
• Can be dereferenced like a pointer variable
s t d : : a rra y < int > myArray = { 5 , 1 0 , 1 5 , 2 0 , 2 5 } ;
s t d : : a r r a y : : i t e r a t o r m yI t e r a t o r , arr a yEn d ;
ar r a yEn d = myArray . end ( ) ;
/ / D em o ns t ra t i n g fo r w ar d i t e r a t i o n
f o r ( m y I t e r a t o r = myArray . b eg in ( ) ;
m y I t e r a t o r ! = a rr ay En d ;
++myIterator )
s t d : : c o ut << * m y I t e r a t o r << ” ” ;
s t d : : c o ut << s t d : : e nd l << ” The end ! ” << s t d : : e n d l ;
/ / Th i s p r i n t s :
/ / 5 10 15 20 25
/ / The end !
23.2.2 Bidirectional iterators
• Everything a forward iterator can do and:
• Can be decremented to move backward in the container to the previous item
s t d : : a rra y < int > myArray = { 5 , 1 0 , 1 5 , 2 0 , 2 5 } ;
s t d : : a r r a y : : i t e r a t o r m y I t e r a t o r , a r r a y B e g i n ;
a r r a y B e g i n = myArray . b e g i n ( ) ;
/ / D em o ns t ra t i n g backward i t e r a t i o n
f o r ( m y I t e r a t o r = myArray . end ( ) ;
m y I t e r a t o r ! = a r r a yB e g in ;
−− myIterator )
s t d : : c o ut << * m y I t e r a t o r << ” ” ;
s t d : : c o ut << s t d : : e nd l << ” The b e g i n n i n g ! ” << s t d : : e n d l ;
/ / Th i s p r i n t s :
/ / 25 20 15 10 5
/ / The b e g i n n i n g !
23.2.3 Random access iterators
• Everything a bidirectional iterator can do and:
• Can use arithmetic operators to move forward and backward a certain num-
ber of items at once
• Allows comparisons between iterators to determine relative positions in the
container
• Can use array-style access to elements in the container
/ / C re a te an a r r ay o f 5 i n t e g e r s
s t d : : a rra y < int , 5> myArray = { 5 , 1 0 , 1 5 , 2 0 , 2 5 } ;
s t d : : a rra y < int , 5 > : : i t e r a t o r m yI t er a to r , array E nd ;
ar r a yEn d = myArray . end ( ) ;
m y I t e r a t o r = myArray . b eg in ( ) ;
/ / Dem on st rat in g random a c c e s s
s t d : : c o ut << m y I t e r a t o r [ 1 ] << ” ”
<< m y I t e r a t o r [ 3 ] << s t d : : e nd l ;
/ / D em o ns t ra t in g i t e r a t o r c o mp a ri s o n s
i f ( m y I t e r a t o r < a rr ayE nd )
s t d : : c o u t << ” N ot a t t h e e nd o f t h e a r r a y y e t ! ”
<< s t d : : e n d l ;
/ / De m ons t rati ng a r i t h m e t i c o p e r a t i o n s on an i t e r a t o r
f o r ( m y I t e r a t o r = myArray . b eg in ( ) ;
m y I t e r a t o r ! = a rr ay En d ;
m y I t e r a t o r += 2 )
s t d : : c o ut << * m y I t e r a t o r << ” ” ;
s t d : : c o ut << s t d : : e nd l << ” The end ! ” << s t d : : e n d l ;
/ / Th i s p r i n t s :
/ / 10 20
/ / N ot a t t h e e nd o f t h e a r r a y y e t !
/ / 5 15 25
/ / The end !
23.3 #include <vector>
Vectors are containers similar to arrays that are flexible in size and quite fast. While
we can use iterators as above, we can also treat the vector much like an array.
/ / S t a r t w ith 1 0 e le me n t s , a l l w it h t h e v a l u e 9 8 . 6
s t d : : v e c t o r < float > t e m p e r a t u r e s ( 1 0 , 9 8 . 6 ) ;
/ / The l a s t e le me nt h as a f e v e r o f 1 0 3 . 1 d e g r e e s !
t e m p e r a t u r e s [ 9 ] = 1 0 3 . 1 ;
f o r (i n t i = 0 ; i < t e m p e r a t u r e s . s i z e ( ) ; i ++)
{
s t d : : c o u t << ” P a t i e n t ” << i << ” ’ s t e m p e r a t u r e i s ”
<< t e m p e r a t u r e s [ i ] << s t d : : e n dl ;
}
e vector class also provides member functions front() and back()
which return references to the first element and the last element in the vector, re-
spectively. For example:
s t d : : c o u t << ” The l a s t p a t i e n t ’ s t e m p e r a t u r e i s ”
<< t e m p e r a t u r e s . back ( ) << s t d : : e n d l ;
s t d : : c o u t << ” The f i r s t p a t i e n t ’ s t e m p e r a t u r e i s ”
<< t e m p e r a t u r e s . f r o n t ( ) << s t d : : e n dl ;
Don’t confuse the back() and front() functions with the end() and
begin() functions. e back() and front() functions return references
to the elements, while end() and begin() return iterators pointing to those
elements.
23.4 #include <map>
is library provides one of the STL’s associative container object classes. An asso-
ciative container differs from an array in that items in an array are referenced with
a number which indicates the item’s position in memory:
i n t myArray [ 1 0 ] ; / / An a r ra y o f t en i n t e g e r s
myArray [ 0 ] = −5; / / S e t t h e f i r s t i n t e g e r in th e a r r a y t o −5
An associative container, on the other hand, can use any data type to reference
the items in the container. For example, you might choose to use a string to
reference a collection of int items to store a list of students’ ages according to
their names.
s t d : : map< s t d : : s t r i n g , int > s t u d e n t s ;
“John”
“Max”
“Christine”
“Maria”
19
ages
string int
19
string int
20
string int
18
string int
map<string,int>
Figure 23.1: Pairing strings and ints in a map object
Perhaps you want to create the object with some initial values:
s t d : : map< s t d : : s t r i n g , int > s t u d e n t s =
{ { ” Joh n ” , 1 9 } ,
{”Max ” , 1 9 } ,
{”Christine” , 2 0 } ,
{” Mari a ” , 1 8 } } ;
is code produces a structure like in Figure 23.1. With these names and ages
paired, we can now retrieve the ages using the names.
s t r i n g name = ” C h r i s t i n e ” ;
s t d : : c o u t << name << ” i s ” << s t u d e n t s [ name ]
<< ” y e a r s o l d . ” << s t d : : e n d l ;
/ / T h is c o de p r i n t s :
/ / C h r i s t i n e i s 20 y e ar s o l d .
New students may also be added in the following way:
s t u d e n t s [ ” Ju n e ” ] = 1 8 ;
s t u d e n t s [ ” Omar ” ] = 1 9 ;
Objects of type map may be iterated, and in C++11, their contents can be
printed in a range-based for loop as we briefly demonstrate here. Each item in the
std::map<std::string, int> is of type std::pair<std::string,int>.
f o r (aut o& i te m : s t u d e n t s )
{
s t d : : c o u t << i t e m . f i r s t << ” i s ” << it e m . s e con d << ”
y e a r s o l d . ” << s t d : : e n d l ;
}
/ / Th i s code p r i n t s :
/ / J oh n i s 1 9 y e a r s o l d
/ / Max i s 1 9 y e a r s o l d
/ / C h r i s t i n e i s 20 y e ar s o l d
/ / M ar ia i s 1 8 y e a r s o l d
/ / J u ne i s 18 y e a r s o l d
/ / Omar i s 19 y e a r s o l d
23.5 Further Reading
• http://en.wikipedia.org/wiki/Standard_Template_Library
• http://www.cplusplus.com/reference/stl/
Index
void functions, 81
Abstract data types, 123
accessors, 126
assignment operator, 5, 11
block comments, 33
casts, 43
class, 107
coefficient, 40
coercion, 43
constructor, 126, 128
count-controlled, 65
dangling pointer, 120
data type, 39
declaration, 4
dereference operator, 111
dot operator, 107, 124
end condition, 61
event-controlled, 65
exponent, 40
extraction operator, 21, 105
File I/O, 103
floating-point types, 39
function body, 80
function call, 79
function declaration, 78
function definition, 79
function heading, 80
header file, 133
identifier, 4
implementation, 134
initializing, 5
input stream, 103
insertion operator, 15, 106
interface, 133
iteration, 61
linked, 133
local variable, 83
loop, 61
lvalue, 11
member function, 107
memory leak, 119
multi-line comments, 33
mutators, 126
narrowing conversion, 43
null character, 72
null terminator, 73
object, 107
object-oriented programming language,
123
output stream, 103
parameters, 78
144
