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From: ar4@sage.cc.purdue.edu (Piper Keairnes)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Why can't the Mac add?
Message-ID: <4485@sage.cc.purdue.edu>
Date: 23 Sep 90 02:05:47 GMT
References: <45060@apple.Apple.COM>
Organization: Purdue University
Lines: 32

In <45060@apple.Apple.COM> das@Apple.COM (David Shayer) writes:

>I was running this simple program.

>main ()
>{
>	float	x; 
>	
>	for (x=0.0;x!=10.0;x+=0.2)
>		printf ("x=%f \n",x);
>}

That isn't that simple of a program when dealing with floating point
numbers. There is no such thing as an EXACT floating point number. Floating
point numbers are close approximations to real numbers. In Mathematics, real
numbers are infinitely accurate, eh? Well, machines are finite. Each 32 or
64 bits of a computer can store a number only so accurately. You start off
at a number near 0 and add a number near 0.2 and expect the computer to end
when the number is near 10. If that is your wish, then just set your
conditional to 'x <= 10.0'

It is not that the Mac is poor at Math. In fact, in a recent homework for
one of my Numerical Analysis classes, we had to approximate a function with
a polynomial. My Mac SE, without math co-processor, got the exact same
answers as did a 10 by '386 processor Sequent Symmetry with math
co-processors. So don't blame Apple... blame either your code, or the people
who designed finite machines ;-)

_____
Piper Keairnes - Computer Science   ** Purdue University Computing Center **
INTERNET: ar4@sage.cc.purdue.edu    **  Unisys Corporation Co-op Student  **
  BITNET: xar4@purccvm.bitnet       **  Macintosh Programmer/ Specialist  **