program to evaluate postfix expression

i am trying to write a program to evaluate postfix expression. i can’t find any error in the code.

but when run it is giving segmentation fault.

someone please explain.especially explain if statement of while loop.

Hi @saurabh2391,

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You didn’t provide an example of a postfix expression you are trying to evaluate. So I can merely guess based on code review.

Problem 1: your numbers are limited to single characters. Line 22 pushes a single character, not a number. E.g.

if your code was working, this postfix expression: “12 4 +” would give you an answer of “6”. The current code pushes ‘1’, then ‘2’, then ‘4’, then pops ‘4’ and ‘2’ to add them.

Problem 2: you are mixing characters (e.g. ‘1’, ‘2’, ‘4’) and numbers. Your stack is declared “stack<char>” but then you pop operand1 / operand2, or push result, and they are integers, not characters.  So lets say your postfix expression is “9 2 *”. The character ‘9’

Both problems would be solved if you:

  • change your operation variable to “stack<int>”

  • when reading digits, convert them to ints

This looks like a good tutorial on postfix.