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From: njt@fisher.UUCP (Nathaniel Thurston)
Newsgroups: net.micro.mac
Subject: Re: Megamax bug?
Message-ID: <1436@fisher.UUCP>
Date: Sat, 14-Jun-86 07:11:58 EDT
Article-I.D.: fisher.1436
Posted: Sat Jun 14 07:11:58 1986
Date-Received: Tue, 17-Jun-86 21:21:00 EDT
References: <1023@k.cs.cmu.edu> <219@analog.UUCP>
Reply-To: njt@fisher.UUCP (Nathaniel Thurston)
Distribution: net
Organization: Princeton University.Mathematics
Lines: 29
Summary: 

In article <219@analog.UUCP> kim@analog.UUCP (Kim Helliwell) writes:
>> 	for (i = ntables; i--; ) <statement>
>> 	if (i == -1) <more statements>
>> 
>> I would expect this to get the value of i, decrement the stored value,
>> and then exit or execute the statement.  Rather, it tests the value
>> before it decrements, and the loop exits with i = 0.  Is this a bug
>> in the code generation, or is C supposed to do this?
>> 
>> 	Greg
>
>	for (i = ntables; ; i--) <statement>
>	if (i = -1) <more statements>
>
>Kim Helliwell

You're both wrong.  The first loop should perform the action Greg describes,
using the value before decrementing.  To have C test the value after
decrementing, use --i.  In the "fix" that Kim gives, the loop will never
exit without a break statement.
The correct code is:
	for (i = ntables; --i; ) <statement>
	if (i == -1) <more statements>
-- 

Nathaniel Thurston
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