CS12, Program 5

Assigned: March 5^th, 2002

Due: March 15^th, 2002, 11pm

Topics

· Inheritance

· Virtual functions and polymorphism

· More pointers

· Character manipulation tools

· Putting together your very own program with multiple files from scratch

Background

A token is a single unit of information. For example, in a computer program, variable names, operators and constants are all tokens. Each type of token is associated with a set of actions. However, some actions are common to all tokens. For example, all tokens can be displayed. For this assignment, you will write a hierarchy of classes for storing tokens read from the input. The base class will store a generic token; two inherited classes will store digits (0..9) and single character operators (+, -, *, =, etc.)

The Program

First you will need to write your classes.

· The base class, called Token, will have two virtual public methods: setValue() to assign the token a value, and display() to display the token in the format discussed below.

· A derived class, Digit, will store single digits in a private int data member. Digit::setValue(char) will assign it a numerical value based on the input parameter, which should be one of the chars in the range ‘0’..’9’. Digit::display() will display the name of the digit (“zero”, “one”, etc.). Five points extra credit if you do this without using a switch and without using a 10-way if/if-else.

· A derived class, Oper, will store operators in a private char data member. Oper::setValue(char) will assign it the value of the input parameter. Oper::display() will display the operator.

Not mentioned above, but still required, are methods such as constructors and destructors. You may add other data members and methods if you think they will enhance your program.

Your program will have an array of pointers to Token. Make your array capable of holding at least 100 pointers. Based on the input, each of these pointers will be assigned the address of a dynamically allocated Digit or Oper object.

The program reads in a stream of digits, operators and white space (space, tab, new line). As each character is read, the program will determine if it is a digit, operator or whitespace (the functions isdigit() and isspace() will come in useful here), and create for it an appropriate token (Digit or Oper), assigning its address to the next pointer in the array. Assign this token a value using setValue(), using the input character as parameter.

When all the input has been processed, go through the array, displaying each token, separating tokens with a single space. Because of the way polymorphism works, you do not nee to know the type of token you have. They are all related by inheritance, and the appropriate display() method will be called. The output loop will look something like this

for (int i = 0; i < array_size; i++)

{

token_array[i]->display();

cout << “ “;

}

where token_array is the name of the array and array_size is the number of tokens processed from the input.

The Input

A sequence of single digits and operators, possibly separated by white space (spaces, tabs, newlines).

For example:

3+41*2/8

-2 + 4*86 - 9

A note on input:

The input should be entered from standard input (keyboard or piped). Read the input character by character using a loop like this:

char c;

while (cin >> c)

{

// process input

}

If you are entering the input from the keyboard, hit ^D (control-d) when done. This will cause cin >> c to return false and you will exit the loop.

The Output

The input sequence, digits translated to words and only a single space between tokens. For the example above, this would be

three + four one * two / eight – two + four * eight six - nine

What to turn in

· token.h

· token.cc

· digit.h

· digit.cc

· oper.h

· oper.cc

· main.cc

Please note:

· Do not use any other names for your files. These names are case sensitive – do not use capital letters anywhere in the file names. Failure to name your files as above will cost you 10 points.

· Please make sure that at least main.cc includes your name, login and lab section. Each is worth 16 points on this assignment. If you are not paying attention, let me remind you that three * one six = four eight. This means that you can barely get half credit if you turn in a perfect program without your info on it.