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From: mcdaniel@adi.com (Tim McDaniel)
Newsgroups: comp.lang.c
Subject: Re: A define problem
Message-ID: <MCDANIEL.91Jan9091908@dolphin.adi.com>
Date: 9 Jan 91 14:19:08 GMT
References: <440@bally.Bally.COM> <1991Jan8.012923.3390@oswego.Oswego.EDU>
	<4613@sactoh0.SAC.CA.US>
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Organization: Applied Dynamics International, Inc.; Ann Arbor, Michigan, USA
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In-reply-to: jak@sactoh0.SAC.CA.US's message of 9 Jan 91 02:09:42 GMT

I suspect that the program Siva Chelliah actually compiled had
   #define half(x)  x /2
without the paren- ^ ^ theses.  In that case, half(i-5) is 3 when i==5.

Rule of thumb: PARENTHESIZE THE RESULT OF A MACRO, AND PARENTHESIZE
THE USE OF EACH ARGUMENT.

Even
   #define half(x) (x)/2
fails, if someone uses it in an expression with an operator with
higher precedence than /, as in
   ~half(i)
This Silly Little Macro should be written as
   #define half(x) ((x)/2)

--
Tim McDaniel                 Applied Dynamics Int'l.; Ann Arbor, Michigan, USA
Work phone: +1 313 973 1300                        Home phone: +1 313 677 4386
Internet: mcdaniel@adi.com                UUCP: {uunet,sharkey}!amara!mcdaniel