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Mail Archives: djgpp/2002/04/10/04:02:11

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From: "Victor Bazarov" <vAbazarov AT dAnai DOT com>
Newsgroups: comp.os.msdos.djgpp,comp.lang.c++
References: <142c67c0 DOT 0204092338 DOT 1ce7acb3 AT posting DOT google DOT com>
Subject: Re: Weird double problem?!
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Date: Wed, 10 Apr 2002 07:46:05 GMT
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

"Taras" <tagas96 AT hotmail DOT com> wrote...
> Just doing some basic programming for maths, and something really
> weird happened.  I'm using RHIDE 1.4.9 w/ djgpp 2.03.  I have this
> line in my
> program:
>   const double stepSize;
>   stepSize = 0.1;

The above code should not compile.  You've declared a const without
initialising it and then you're modifying a const value without any
const-cast.  You probably meant

    const double stepSize = 0.1;

> when i step through the program and watch the variable step size, when
> it
> is assigned the value of 0.1, in the watch window it says the value is
> 0.10000000000000001.  I don't think it has something to do with the
> displaying of the number, because when I store the result of
> 1/stepSize
> into an integer variable, the value of that variable is 9 (when it
> should be
> 10) Does anyone know where the last digit came from?

From the fact that 1/10 cannot be represented _precisely_ in your
computer memory.

Please remove capital A's from my address when replying by mail

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