Converting From Prefix to Infix: The Stack Method

Here is the algorithm we will use for converting from infix to prefix:

1. Reverse the expression

2. Read expression one character at a time

3. Depending on character read:
        ")": Push onto stack
        Operator: Push onto stack
        Operand: Push on and pop off (straight to output)
        "(": Keep popping until corresponding ")" is encountered

4. Reverse the output

And that’s it!

For now you can use the stack code from Moodle to practice, but we’ll shortly have an interactive version here too.