swap(x,y)

[Timothy R. Gottschalk]

       To swap two variables x,y in C without using a temporary variable:

       /* begin swap */
       x += y;
       y = x - y;
       x -= y;
       /* end swap */

       Just curious...(this looks pretty valid) does anyone know an even
simpler method?  I would never program this way -- it's more of a theory
question.  I've been told that it can't be done (???).
Tim Gottschalk
Pgh, PA