If you are going to do it from a character array and can assume integer values, then when you get a numeric value, you will need to accumulate the number, but you won't generally be able to store that in a char variable.

There are generalized parsers available (use Google), but if I were going to write one, I would not start with a character array, but parse "tokens" that would be math symbols, keywords, numbers, variable names, etc.

15,666,844 members

If you want to handle translating infix's operator-precedence and nested parentheses: that requires a recursive descent parser: http://en.wikipedia.org/wiki/Recursive_descent_parser ... do you want to learn how to write one ?

Example: infix 5 + 11 * 5 = 60 because * has greater precedence than +, so to write that out in postfix, you need to translate to:

5 11 * 5 +