Message-ID: <3AB314CE.F5DAD6A3@earthlink.net>
From: Martin Ambuhl <mambuhl AT earthlink DOT net>
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Subject: Re: Whats up with sqrt?
References: <5BF60CD649EDD411A04600B0D049F53A09257B AT hydmail02 DOT hyd DOT wilco-int DOT com> <8ugkfne00UjFETbF0i AT andrew DOT cmu DOT edu>
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Date: Sat, 17 Mar 2001 07:37:11 GMT
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To: djgpp AT delorie DOT com
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James W Sager Iii wrote:
> 
> Excerpts from netnews.comp.os.msdos.djgpp: 17-Mar-101 RE: Whats up with
> sqrt? by Prashant Ramachandra AT wil
> >
> > On Saturday, March 17, 2001 10:49 AM, James W Sager Iii
> > [SMTP:sager+@andrew.cmu.edu] wrote:
> > | For me, the function sqrt() which obviously returns a square root
> > | is
> > | messing up for me on moderately large numbers.
> > |
> > | anything below 10,000 and it gives me about the right answer, but at
> > | like:
> > |
> > | range = sqrt(300,000)
> > |
> > | I get a 0 as a return value?  I tried doing:
> >
> > Don't use commas while sending parameters. It's giving you the square root
> > of the second parameter, i.e. 0.
> >
> > range = sqrt (300000.0);
> >
> > is the right way to do it.
> 
> I'm sorry, I wasn't using commas... but at the same time I wasn't using
> 0. so perhaps it was being type casted wrong.
> 
> but I tested it
> a=sqrt(10001.0);
> 
> returns 100516
> 
> Ok, that makes no sense what so ever
> well at least I have my own function to do it no biggie

Frankly, I don't believe you about the behavior you claim.  Since you
don't post the misbehaving code, we can only guess what you are doing wrong.
(My guess is failure to include appropriate headers and failure to enable
reasonable warnings.) Notice the following:

#include <math.h>

int main(void)
{
    double a;
    a = sqrt(300000);
    printf("sqrt(300000) returned as %g;\n"
            " %g*%g=%g\n", a, a, a, a * a);
    a = sqrt(10001);
    printf("sqrt(10001) returned as %g;\n"
            " %g*%g=%g\n", a, a, a, a * a);
    return 0;
}

sqrt(300000) returned as 547.723;
 547.723*547.723=300000
sqrt(10001) returned as 100.005;
 100.005*100.005=10001