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From: roelof@idca.tds.PHILIPS.nl (R. Vuurboom)
Newsgroups: comp.lang.c
Subject: Re: swap(x,y)
Message-ID: <228@ssp1.idca.tds.philips.nl>
Date: 22 Aug 89 17:08:11 GMT
References: <MYwDEFy00WB842JEUx@andrew.cmu.edu>
Organization: Philips Telecommunication and Data Systems, The Netherlands
Lines: 42

In article <MYwDEFy00WB842JEUx@andrew.cmu.edu> tg1e+@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);
}

-- 
I don't know what the question means, but the answer is yes...
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Roelof Vuurboom  SSP/V3   Philips TDS Apeldoorn, The Netherlands   +31 55 432226
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