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June 16, 2008 |
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Description
Objectives:
This assignment aims to review C++ skills or concepts including:
C++ classes
Separate compilation
Stacks
Command-line arguments
Reading from a file
Task: A Calculator Program
In this project, you will write a program that acts as a simple calculator.
Description
This program will be reading a file that contains an arithmetic expression on each line. The program evaluates these expressions and prints the values to cout.
The expressions will be postfix expressions (as described on pages 373--376 of the text). Your program will be implemented using a stack-based algorithm for evaluating an arithmetic expression.
Getting Started
Read all of Chapter 7, with particular attention to Section 7.4.
To help you get started, the following files will be supplied:
the stack header file stack2.h
the stack template file stack2.template
the node header file node2.h
the node template file node2.template
N.B.Your program must use this startup files in its implementation
This project requires you to read a file, specified in the command line arguments when the program is executed, and output the resulting answers to cout.
The input expressions contained in the file will be postfix expressions.
Use the evaluation algorithm from Figure 7.10 on page 376 of the text.
Additional Functions
Include the following three functions in your implementation
A function that opens a file for input and checks that the opening process did not fail. The specification for this function is:
void open_for_read(ifstream& f, const char filename[ ]);
// Postcondition: The ifstream f has been opened for
// reading using the given filename. If any errors
// occurred then an error message has been printed
// and the program has been halted.
A boolean function that determines whether a specified file still has valid input. The specification is:
bool is_more(istream& f);
// Postcondition: The return value is true if f still has
// more valid input to read; otherwise the return
// valid is false.
Notice that the data type of the argument is an "istream" rather than an "ifstream". An istream is usually an ifstream, although later you will learn of other kinds of istreams (such as cin). Istream arguments must always be reference parameters.
A function named process_line with this prototype:
void process_line(istream& f, bool& okay, double& answer);
One useful technique that you might use when you first start to implement this function is to firstly implement a simple version of the process_line function.
The simple version reads one input line, sets okay to true, and sets answer to 42.0 (Later you will implement a more complex version of the function that actually evaluates an arithmetic expression from the input line).
Put the simple version in your source code and change the body of the main function so that it does this:
Declares an ifstream variable called input and uses open_for_read to open input for reading. Use argv[1] as the name of the input file.
Have a loop that continues while there is more input. In the body of the loop, call process_line. If process_line sets okay to true then print the value of answer on the next output line; otherwise print the word INVALID on the next output line.
Close the input file and print a message saying that the program is done.
The possible errors that will cause okay to be set to false:
(a) division by zero,
(b) an operation symbol is read but the stack does not have at least two numbers,
(c) the entire expression has been read and evaluated but the numbers stack does not have exactly one number on it.
If an error is detected, be sure to continue to read the rest of the input line (up to and including the newline character).
Use input techniques similar to those in Figure 7.5 on pages 361-362.
Reminder
You may not start working in this and any request before
your bid is accepted. Users who violate this policy
may have their accounts permanently suspended.
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