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From: silvert@cs.dal.ca (Bill Silvert)
Newsgroups: comp.lang.pascal
Subject: Re: Problem in Turbo Pascal 4.0
Summary: Don't check for equality with reals
Message-ID: <1989Dec30.135702.12086@cs.dal.ca>
Date: 30 Dec 89 13:57:02 GMT
References: <4658@ur-cc.UUCP>
Sender: silvert@cs.dal.ca.UUCP (Bill Silvert)
Reply-To: bill@biomel.UUCP
Organization: Habitat Ecology Div., Bedford Inst. of Oceanography
Lines: 28

In article <4658@ur-cc.UUCP> lowj_ltd@uhura.cc.rochester.edu (John Alan Low, aka "Travis" Low) writes:
>I am having a problem with Turbo Pascal 4.0. The repeat loop in the following
>loop never terminates. 
> 
>Program Foo;
>var  x : real;
>Begin
>x := 0.10;
>     Repeat
>     x := x + 0.01;
>     Until x = 0.30;
>End.

You should never check for equality with reals.  Computers do their math
in binary, not decimal, and 0.30 is a continuing binary fraction.
Change the test to:

>     Until x >= 0.30;

or, better, to

>     Until x >= 0.2999;

-- 
Bill Silvert, Habitat Ecology Division.
Bedford Institute of Oceanography, Dartmouth, NS, Canada B2Y 4A2
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