How to compare a negative number??

Hi there!

I'm new at arduino, but learning fast. Now I'm working with 2 motors and 2 encoders.
I was getting the code quite well but now I' struck
I use expresions like this al the time:

if( x < y) {.........

But, what's wrong with this expresion:

if(x < (y * (-1)) {.........

Or this:

if(x < (-y))

How can I make this work????

Thanx!!!

Out of context, I don't see anything wrong, but the types of the variables may make such a comparison pointless.
Which is why we ask you to post your code.

Assuming that x and y are signed, this should work. What exactly is the problem?