Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!ukc!strath-cs!rmacfarq
From: rmacfarq@cs.strath.ac.uk (Roderick F MacFarquhar IE87)
Newsgroups: comp.lang.c
Subject: Re: Brain Teaser
Summary: Exclusive OR
Keywords: { void * x, * y; x <-> y; }
Message-ID: <2817@baird.cs.strath.ac.uk>
Date: 28 Mar 90 10:03:03 GMT
References: <10289@wpi.wpi.edu>
Reply-To: rmacfarq@cs.strath.ac.uk
Organization: Comp. Sci. Dept., Strathclyde Univ., Scotland.
Lines: 34

In article <10289@wpi.wpi.edu> oesterle@wpi.wpi.edu (Shawn H. Oesterle) writes:
>
>Problem:
>	Swap two pointers without using a third pointer.

        [code using temp deleted]

>Hint:
>	Two numbers may be swaped without using any other memory by executing
>	the following statements:
>
>	int x, y;	/* or you can chose double, long, etc. */
>
>	x += y;
>	y = x - y;
>	x -= y;

But isn't there is a problem of potential overflow on the x += y instruction.

I think its been given before in this group but how about..

#define SWAP(X,Y) \
	{(X) ^= (Y) ; \
	 (Y) ^= (X) ; \
	 (X) ^= (Y) ;}

>Shawn Oesterle {oesterle@wpi.wpi.edu}

_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
 Roderick MacFarquhar - Information Eng IV, Strathclyde University 
 Janet rmacfarq@cs.strath.ac.uk    Internet rmacfarq%cs.strath.ac.uk@nsf.ac.uk 
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