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Groups > comp.lang.c > #26609

Re: Swapping logic

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On 9/23/12 8:48 AM, ZUBAIR TRALI wrote:
> #include<stdio.h>
> /*new logic for swapping*/
> #include<conio.h>
> void main()
>  {
>    int x=20,y=30;
> printf("nos before swapping are %d and %d\n",x,y);
>     x=x*y/(y=x);
> printf("nos after swapping are %d and %d\n",x,y);
> getch();
> }
> 

This invokes undefined behavior, as you set the value of y, and also use
the value of y (for a purpose other than getting the value to set y to).
The language does not promise that the sub expression x*y will be
executed before the sub expression y=x.

Also, x*y needs to fit withing the range of an int, so it will only work
for "small" numbers, and it fails if y == 0 (as 0/0 again invokes
undefined behavior).

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Swapping logic ZUBAIR TRALI <bhat.zubair789@gmail.com> - 2012-09-23 05:48 -0700
  Re: Swapping logic Richard Damon <news.x.richarddamon@xoxy.net> - 2012-09-23 09:04 -0400
  Re: Swapping logic Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-09-23 09:15 -0400
    Re: Swapping logic Noob <root@127.0.0.1> - 2012-09-24 12:56 +0200
  Re: Swapping logic Casey Carter <Casey_at_Carter_dot_net@dontspam.me.invalid> - 2012-09-23 11:35 -0500
    Re: Swapping logic Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-09-23 14:19 -0400
      Re: Swapping logic Nobody <nobody@nowhere.com> - 2012-09-24 10:57 +0100
      Re: Swapping logic Andrew Smallshaw <andrews@sdf.lonestar.org> - 2012-09-26 05:20 +0000
        Re: Swapping logic Gareth Owen <gwowen@gmail.com> - 2012-09-26 06:46 +0100
          Re: Swapping logic David Brown <david@westcontrol.removethisbit.com> - 2012-09-26 08:16 +0200
            Re: Swapping logic Gareth Owen <gwowen@gmail.com> - 2012-09-26 17:51 +0100
  Re: Swapping logic Kaz Kylheku <kaz@kylheku.com> - 2012-09-23 18:19 +0000

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