Question

After doing some research, I learned about the postfix notation, and how to parse an expression.

My code converts to postfix notation, and then it evaluates it using the stack based method. For example:

Initial expression: 5 + 2^(4 - 1)
Postfix notation: 5 2 4 1 - ^ + 
Result: 13

Now I am trying to expand this program to be able to evaluate expressions with functions, like sin, cos, log, for example: 5 + sin (2 + log (2)).
My initial idea was, before parsing it, to find these functions, evaluate their results, and replace it in the string. But I don’t think it’s a very good idea…

So how can I do this in an efficient way?

Here is some code written in c#, if it is of any use: http://pastebin.com/7wB81fyQ, but I would prefer some pseudo-code so that I understand what I am writing better… I’m not one of those guys who just copy and paste.

Answer 1

Treat these functions like any other operator plus braces. First calculate what’s in the braces, then execute the function.

Initial: 3 * Sin(4 + 5)
Postfix: 4 5 + Sin 3 *       (that's how I would enter it in a HP calculator)
or:      3 4 5 + Sin *

Other than +, which consumes two numbers, Sin consumes only one number.