May 08 2007

Digression into Swaps

Published by Lucello at 3:13 pm under Geeky

Did you know you can swap the value of two variables without temp??

$a = $a + $b;
$b = $a - $b;
$a = $a - $b;

I wish I were so clever as to come up with that on my own. Still, I post it here to spark the imagination of those who find it as fascinating as I.

;-)

6 Responses to “Digression into Swaps”

  1. # Lucelloon 08 May 2007 at 3:17 pm

    I should point out that this post arose from a pasta gratin, the baking of which required a swap of two pans to different racks in the oven. Many thanks to Jeremy for englightening us on this subject.

    :)

  2. # BunnyToasteron 08 May 2007 at 9:38 pm

    If you worry about arithmetic overflow, XOR comes to the rescue

    #include

    main() {
    int a =5;
    int b=7;

    a = a ^b;
    b = b ^a;
    a = a^ b;

    printf (”%d %d\n”, a , b);
    }

  3. # Michion 09 May 2007 at 3:14 pm

    Neat, I can vaguely remember doing that once in a programming class two years ago. Now it will hopefully stay on my mind!

  4. # saintamhon 03 Jun 2007 at 1:27 pm

    Oh, that’s cool! This:

    ($a, $b) = ($b, $a);

    would also do the job (in Perl) and might be a bit more readable :)

  5. # mfalcon24on 06 Jun 2007 at 5:21 am

    That is cool… not sure if C++ compilers would keep the optimization in however - if you really need to cut the extra variable out it might be best to do it in assembly.

  6. # moeffjuon 11 Jul 2007 at 3:52 pm

    Am I ever glad to program in sane languages that can do swapping on one line, like Perl (but Python is much better).

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