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CS211 – Programming Practicum

Fall 2018

Programming Project 6
Due: Wednesday, 11/21/18 at 11:59 pm

Can I Get There from Here?
For this program, you will write a C++ Program to represent a travel network. This travel network will
use an array of linked lists as its primary storage structure. This type of storage structure is typically
called an “adjacency list”.
Please note: this write-up was originally taken from a non-C++ assignment. Any reference to non-C++
items were not properly “translated” into C++. Such items should use their C++ counterparts.
Assume you have a small airline that flies planes between a small number of airports. Each airport will
be given a number. If a plane flies from airport X to airport Y, the network will have an “edge” from X
to Y. Below are a number of drawings that could represent this idea. The airports are represented by the
circled numbers, the edges are represented by the arrows. Consider the first drawing. It has 6 airports.
It has a plane that flies from airport 1 to airport 2. Three planes fly from airport 2, one to airport 3, one
to airport 4 and one to airport 5. No planes leave from airport 3 or from airport 5 (yes, it would be
stupid to strand planes at those airports, but ignore that fact for now). Planes fly from airport 4 to
airports 5 and 6. Finally, planes fly from airport 6 to airport 3.

In an adjacency list, each location/airport needs a list of those locations/airports that one can get to in
one move/flight. In this program, we need a list for each airport. If the travel network has N airports,
the array will have N linked lists, one for each airport. If airport X has planes flying to 3 different
airports, the linked list for airport X would have 3 nodes. Consider the following image showing a
travel network and an adjacency list:

CS211 – Programming Practicum

Fall 2018

There are 5 airports, so we have an array of 5 linked lists. Since Airport 3 can fly planes to two
Airports, namely Airport 1 and Airport 4, the linked list for Airport 3 has two nodes: one node
containing the value 1; another node containing the value 4.

Program Input and Commands
The input for the operations will come from standard input and from files. The input will initially come
from standard input. If the user specified the f command, your program will then read input from a file.
See the description below for more details. The commands are to follow the descriptions given below.
Note: that the form  could be any integer number and it will NOT be enclosed in angle brackets.
 is just a notation to specify and integer value. The integer value is to be input on the same line as
the command character. If the first character on the line is not one of the following characters, print an
error message and ignore the rest of the information on that line.
q

- quit the program immediately.

?

- display a list of the commands the user can enter for the program.

#

- ignore this line of input. Treat the line of input as a comment

t   - display a message stating whether a person can travel from airport  to airport
 in one or more flights.
r 

- remove all values from the traffic network and resize the array to contain the number
of airports as indicated by the given integer value. The value of the integer must be
greater than zero. The airports will be numbered from 1 to the given integer value.
Be sure to deallocate all unused memory as part of this command.

i   - insert the edge to indicate a plane flies from airport  to airport .
d   - delete the edge that indicates a plane flying from airport  to airport .
l

- list all the items contained in the travel network. First display all of the airports (if any)
that can be reached from the airport #1 in one flight (that have an edge in the network),
followed by all the airports (if any) that can be reached from airport #2 in one flight, etc.

f 

- open the file indicated by the  (assume it is in the current directory) and
read commands from this file. When the end of the file is reached, continue reading
commands from previous input source. This must be handled using recursion. Beware
of a possible case of an infinite recursive loop, the f command is may not call a file that
is currently in use.

Initially your program should have the array to hold 10 airports (numbered 1 to 10). If a
command specifies an airport outside of the current valid range, print an error message and ignore the
command.
The code given in proj6Base.cpp should provide the basics on reading input. You will need to do some
cutting and pasting of code to read in input for all commands. The input is properly read in for the t and
f commands. It is assumed that you can determine the code for the rest of the commands by looking at
the code those these two commands.

CS211 – Programming Practicum

Fall 2018

Travel Algorithm and the Airport Object
To determine if a person can travel from airport X to airport Y in one or more flights, a recursive depthfirst-search algorithm must be used. For this algorithm to work, we will need to be able to mark each
airport as visited. Setting up an Airport class is required. This object will contain all of the data that one
airport knows (the head of the linked list for the airport’s adjacency list and the object will also contain a
Boolean value to determine if an airport has been visited or not) and the methods to use that data. The
travel network MUST be a dynamic array of these Airport objects. The adjacency list will also need a
Node class/object to store the linked list information.
The pseudo code for this algorithm is as shown below. Note it is valid to ask, can I to go from airport X
to airport X in one or more flights. It really asks, “If I leave airport X, can I return to it?” This
algorithm is recursive and you MUST use this recursive algorithm in your program.
void depthFirstSearchHelper (int x, int y)
{
mark all airports as unvisited;
if ( dfs (x, y) = = TRUE)
print (“You can get from airport “ + x + “ to airport “ + y + “ in one or more flights”);
else
print (“You can NOT get from airport “ + x + “ to airport “ + y + “ in one or more flights”);
}
boolean dfs (int a, int b)
{
for (each airport c that can be reached from a in one flight)
{
if (c = = b)
return TRUE;
if ( airport c is unvisited )
{
mark airport c as visited;
if ( dfs (c, b) = = TRUE )
return TRUE;
}
}
return FALSE;
}

The FILE Command: f
The f command may seem difficult to implement at first, but it has a creative solution that you are to
use. The code in the file Proj6Base.cpp is intended to give you an idea on how this solution is to be
implemented.
First note that main( ), is extremely short. It just creates an instance of the TravelNetwork class and
calls the processCommandLoop( ) method with an value of FILE* that reads from standard input.
The method processCommandLoop( ) reads from the input source specified by the parameter and
determines the which command is being invoked.

CS211 – Programming Practicum

Fall 2018

When the f command is invoked, it is to open the file specified by the command, create a new instance
of FILE* that reads from this file. Then make a recursive call to processCommandLoop( ) with this new
instance of the FILE* so the next line of input comes from the specified file instead of where the
previous command came from. When the end of a file is reached, the program is to revert back to the
previous input source that contained the f command. This previous input source could be standard input
or a file. By making these calls recursively, reverting back to the previous input source is a complete
no-brainer.
However, this can cause an infinite loop if you try to access a file that your program is already reading
from. Consider this scenario. Assume the user enters a command from standard input to start reading
from file A. However; file A tells you to read from file B, file B tells you to read from file C, and file C
tells you to read from file A. Since you always start reading from the top of the file, when file C
eventually tells the program to read from file A, the program will reprocess the command to read from
file B, which will reprocess the command to read from file C, which will reprocess the command to read
from file A, which will reprocess the command to read from file B, which will reprocess the command
to read from file C, which will reprocess the command to read from file A, which will reprocess…
In order to stop this, you are required to maintain a linked list of file names. Before the f command
attempts to create a new instance of FILE* that read from file X, the f command is to check if the linked
list of file names already contains the name of X.
• If the name X already exists in the linked list, the f command will NOT create a new instance of
FILE* and it will NOT make the recursive call to processCommandLoop( ).
• If the name X does not exist in the linked list, the f command will add the name X to the linked
list before making the recursive call to processCommandLoop( ) and it must remove the name X
from the linked list after the call to processCommandLoop( ) returns.
You are responsible to write the code for this linked list yourself. Note that this will most likely be a
linked list of Strings, while each airport’s adjacency list will most likely be a linked list of integers.

Classes You Must Write
First, you are to write a class called Airport. This class is to contain everything that is known about a
specific Airport. This MUST include the airport’s adjacency list and the “visited” status for the Depth
First Search.
Next, you must write a list class. You are encouraged to name the class MyList as the name “List” is
already used in the C++ Standard Template Libraries. Please note that your list class will need another
class for the nodes in the list. Thus you must write a class called MyNode also. For your list class, in
addition to the normal insertValue( ) and deleteValue( ) operations, you may want to write operations
such as getNumberOfCurrentsValues( ) and getNthValue( ).
The TravelNetwork class has been started for you. This class must contain the array of Airports and the
linked list of filenames for the “in-use” files needed for the f command.
All data members (or “instance variables”) must be made private. Failure to do this will result is a
severe reductions of points for the project.

CS211 – Programming Practicum

Fall 2018

You are not allowed to use any of the classes from the C++ Standard Template Libraries in this
program. These classes include ArrayList, Vector, LinkedList, List, Set, Stack, HashMap, etc. If you
need such a class, you are to write it yourself. These are sometimes called the C++ Standard
Container Library. A full listing of the C++ Standard Template Libraries can be found at:
http://www.cplusplus.com/reference/stl/

Multiple Source Code Files
Your program is to be written using at least two source code files. One of the source file files is to
contain the main function of the program named in a file using your NetId and Program name, like:
Ptroy1Proj6.cpp
The other source code file must contain your Airport class in a file named:
Airport.cpp
You may use additional source code files if you wish (i.e. MyList.cpp), but these two are required. The
above implies that you will need to write any appropriate .h file(s) and a makefile.

Coding Style
Don’t forget to use good coding style when writing your program. Good coding style makes your
program easier to be read by other people as the compiler ignores these parts/differences in your code.
Elements of good code style include (but may not be limited to):
•
•
•
•
•
•
•

Meaningful variable names
Use of functions/methods
Proper indentation
Use of blank lines between code sections
In-line comments
Function/method header comments
File header comments

The Code Review Checklist also hints at other elements of good coding style.

Program Submission
You are to submit the files for this project as a single zip file via the Assignments Page in Blackboard.
To help the TA, zip your files together and name your zip file with your net-id and the assignment name,
like: Ptroy1Proj6.zip



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