postfix help

[tarja]

Hi all, i'm stumped

I'm suppose to write a program that evaluates postfix arithmetic expressions using stacks. any ideas how to turn this into something easy even a simple-mind like myself could understand?

The user types numbers in postfix and it is suppose to output the answer. So, it would look like this : 4 5 2 7 + - * = 16

Any help on this would be greatly appreciated!

Thanks.

~ Tarja

[Valmont]

This is easy but good intro in expression evaluation.

- You have a stack with numbers in it.
- You have some datastructure with the operators in it in the right order of execution.

1) Pop top number of stack and store in a variable.
2) Pop second number of stack and store in another variable.
3) Fetch operator and use it on those two variables.
4) Push result on stack.

Do this until one number and no operators are left. The last number is the answer. If an operator is left with only one number on stack then the expression is invalid.

Good luck!

[Valmont]

So how did it go tarja?