rpn - handling unary minus for shunting-yard algorithm

Question

Is there a better way to handle unary "-" in converting a infix expression to a postfix one?

The obvious one would be prefix every unary "-" with a 0. Does anyone know better implementation? Thanks!

Answer 1

The way I did this years ago was invent a new operator for my postfix expression. So when I encountered a unary minus in the infix, I'd convert it to #. So my postfix for a + -b became ab#+.

And, of course, my evaluator had to know that # only popped one operand.

Kind of depends on how you're using the postfix expression once it's built. If you want to display it then your special # operator would probably confuse people. But if you're just using it internally (which I was), then it works great.