Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!hp4nl!eutrc3!tuewsd!wsinkees
From: wsinkees@lso.win.tue.nl (Kees Huizing)
Newsgroups: comp.lang.pascal
Subject: Re: Problem in Turbo Pascal 4.0
Keywords: Nonterminating Repeat loop, real, representation
Message-ID: <803@tuewsd.lso.win.tue.nl>
Date: 3 Jan 90 13:59:50 GMT
References: <4658@ur-cc.UUCP> <4660@ur-cc.UUCP>
Organization: Eindhoven University of Technology, The Netherlands
Lines: 33

lowj_ltd@uhura.cc.rochester.edu (John Alan Low) writes:

>In article <4658@ur-cc.UUCP> I wrote: 
>>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.

>     Thanks to everybody who emailed me on this. I forgot that 0.01 is a
>     repeating decimal in binary. I never will again.
>  ....
>     Thanks again for all the help. (Boy, do I feel stupid)
                                      ^^^^^^^^^^^^^^^^^^^^^
It's not you that is stupid, it's (Turbo?) Pascal.  Is it not the purpose of
a high level pogramming language to hide the funny details of implementation
and representation for the user?  As it shows, the equality operator
"=" does not on reals what it pretends to do.  I accept that it cannot
detect perfect equality of reals, but what it could do is detect equality
upto some representation dependent accuracy.  

Why is it not done this way?

						Kees

-- 
Kees Huizing - Eindhoven Univ of Techn - Dept Math & Comp Sc - The Netherlands
DOMAIN: wsinkees@win.tue.nl    BITNET: wsdckeesh@heitue5    FAX: +31-40-436685