can't figure this out

[Gaminic]

That, too, will loop forever. The proper way is this:

while (a-b>0) {
  a -= b;
}

[edit] But Moschops' trick is much more elegant.

[Nisheeth]

Oh God!! That's what comes of not sleeping by midnight!
The final correction (it becomes the same as yours after that by the way):

int c = a;
while (c-b>0) 
{
  c = c- b;
}