Infix To Postfix Conceptual

Question

I'm currently studying for a final right now, and this is something I never understood how to do. On one of my homework questions, I was asked whether some provided postfix expressions were valid or invalid. Is there any surefire way to know this?

Thanks

Answer 1

Evaluate it. Push each number; when you encounter an operator, pop two values, apply the operator to them, and push the result. There should be no stack underflows, and at the end there should be exactly one stack element.