swap(x,y)

[R. Vuurboom]

In article <MYwDEFy00WB842JEUx at andrew.cmu.edu> tg1e+ at andrew.cmu.edu (Timothy R. Gottschalk) writes:
>
>       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 (???).
						   ^^^
						   hey ma, thars one o dem
						   trigraphs again...:-)

This algorithm caught me out once. Try the following:

#define swap(x,y)  { x += y; \
		     y = x-y; \
		     x -= y; }

main()
{
	int i = 3;
	int j = 4;

	swap(i,j);
	printf ("i = %d  j = %d\n",i,j);

	i = 3;

	swap(i,i);
	printf ("i = %d\n",i);
}

-- 
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