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From: linden@adapt.Sun.COM (Peter van der Linden)
Newsgroups: comp.lang.pascal
Subject: Re: Problem in Turbo Pascal 4.0
Keywords: Nonterminating Repeat loop
Message-ID: <129757@sun.Eng.Sun.COM>
Date: 30 Dec 89 19:05:44 GMT
References: <4658@ur-cc.UUCP>
Sender: news@sun.Eng.Sun.COM
Reply-To: linden@sun.UUCP (Peter van der Linden)
Organization: Sun Microsystems, Mountain View
Lines: 29

> Reply-To: lowj_ltd@uhura.cc.rochester.edu (John Alan Low, aka "Travis" Low)
> 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.

Another programmer discovers inexact representation of decimals as binary reals!
What is happening is that your literals are not *exactly* representable as
binary floating point numbers.  Hence the loop termination test is never
satisfied.  The routines that print, also round, so you never saw this.

You can change the test to "until x >= 0.30" instead of multiplying.  If you
have access to a Sun system, read the "Floating Point Programmers Guide"
(purple tab in the docu-box).   







----------------
Disclaimer: I'm no Jack Kennedy, but I'm no Dan Quayle either.
Peter van der Linden     linden@SuN.cOm    (415) 336-6206