how to change a positive number to negative and vice versa?

Question

I'm thinking there must be a function to do both. I think fabs will do negative to positive.

But not sure about the other way around ?

Answer 1

I would rather write like this:

num = -num;

This won't need a multiplication, just changing the sign.

Answer 2

num *= -1 will change the sign from positive to negative and vice versa.