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Re: Re: Re: non-perl SQL question

by Roger (Parson)
on Dec 31, 2003 at 11:59 UTC ( [id://317872]=note: print w/replies, xml ) Need Help??


in reply to Re: Re: non-perl SQL question
in thread non-perl SQL question

Thanks. ;-)

I first had this idea 12 years ago, during a first year C programming lecture at University. The professor declared in the class that if you want to swap the values of two variables, you have to do it with a temporary variable:
X=5 Y=6 # to swap X and Y, introduce a temporary variable Z Z=X X=Y Y=Z
I challenged his declaration and provided the following solution in 2 steps without a third variable:
X=X+Y Y=X-Y X=X-Y # I know this solution is not perfect: # when X and Y are big, there is a danger of overflow.
The lecturer was amazed and gave me an 'A' for the subject. *grin*

The solution set order_id=11-order_id where order_id in (5,6) is just another variant of the same trick.

Update: Thanks rkg to point out the missing bit. My memory got rusty. The original challenge was to swap the values without using a third temporary variable.

Replies are listed 'Best First'.
Re: Re: Re: Re: non-perl SQL question
by rkg (Hermit) on Dec 31, 2003 at 12:18 UTC
    am i missing something?
    x=5 y=6 x=x+y # x = 5+ 6 = 11, yes? y=x-y # y = 11 - 6 = 5, yes?
Re: Re: Re: Re: non-perl SQL question
by CountZero (Bishop) on Jan 01, 2004 at 22:48 UTC
    But of course only with numerical values, not with string data.

    CountZero

    "If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law

Re^4: non-perl SQL question
by Anonymous Monk on Jul 09, 2004 at 21:56 UTC
    Thanks alot. You saved me now half a year later

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