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From: mjs@sfsup.UUCP (M.J.Shannon)
Newsgroups: net.sources.bugs
Subject: Re: A good checkbook acct. program
Message-ID: <122@sfsup.UUCP>
Date: Sat, 8-Feb-86 01:11:11 EST
Article-I.D.: sfsup.122
Posted: Sat Feb  8 01:11:11 1986
Date-Received: Tue, 11-Feb-86 05:39:54 EST
References: <440@drutx.UUCP> <310@isis.UUCP>
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Organization: AT&T Information Systems, Summit N.J.
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> I was using this checkbook program as an example in a course, plugged in some
> realistic numbers, and found it was coming up off by a cent, then two cents
> a bit later...  What I found was that 'awk' on this system was using floats
> for all the real values, rather than doubles.
> 
> For instance: % awk 'BEGIN {printf "%f\n", 12345.67 ; exit}'
> 12345.669922
> 
> As this is off by .008 of a cent, after 125 of these you get close to losing
> a penny.  Of course some representations will be over, and some under,
> but do you really want to trust your balance to fate?
> 
> Andrew Burt
> isis!aburt   or   aburt@udenver.csnet

But all banks use fixed point arithmetic.  This has the advantage of
being almost as fast as integer arithmetic, as well as preventing
representation/roundoff errors.  If you change the semantics of your
program to store cents (rather than dollars), you can probably eliminate
such errors (unless awk uses float/double for all numeric ops).

	Marty Shannon
	AT&T-IS Computer Systems
	(201)-522-6063