CS 291
Project 2

Due: December 22 (No Exceptions!)

Design and write a program that evaluates a postfix expression.  You must use 
the algorithm we discussed in class.  The program must input a string postfix expression and  
evaluate the expression.
The program must work for all integers (one or more digits).  To do this you can
implement the string_to_integer function that we discussed in class.
For example, the program must evaluate a postfix expression such as

10_20_50_+_*


Also required, the program MUST handle input errors.  That is, if the following expression is input: 

10_20_30_+

The program should return an appropriate error message (much like a compiler).
An appropriate error message would be: "Insufficient operations" or "Too many
operands."

Similarly, if an expression such as:

10_20_+_*

is entered, the program must return an appropriate mussage for this expression.
Such an error message could be: "Too many operations" or "Insufficuent operands"

Deliverables:
1.) A complete program listing
2.) A program description
3.) A written description on how you wrote the program, data structures used,
    input requirements, etc.
4.) Test runs and analysis of these runs.