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From: ravim@gtenmc.UUCP (Vox Populi)
Newsgroups: comp.lang.c
Subject: Re: Problem with #define'd macro...
Message-ID: <1099@gtenmc.UUCP>
Date: 29 Mar 91 01:55:30 GMT
References: <1991Mar20.150301.9941@evax.arl.utexas.edu>
Reply-To: ravim@gtenmc.UUCP (Ravi Kumar Mandava)
Organization: GTE Telecom, Inc.  Bothell, WA
Lines: 27

In article <1991Mar20.150301.9941@evax.arl.utexas.edu> c145gmk@utarlg.uta.edu writes:
>Attempting to compile the following (fragment, but displays the problem)
>results in an 'invalid target for assignment' error on our VAX running

>
>#define DIV_MOD(d,r,x,y) ( y == 0.0 ? d = 0.0, r = x : d = x/y, r = x - d*y )

>a = 5, b = 2; DIV_MOD(quotient,remainder,a,b);

I think the compiler error that you were getting is because, operator
precedence is not observed here correctly.

According to K&R precedence table, operator ',' has lower precedence (in fact,
least precedence) than the tertiary operator '? :'. 
Hence you would need to raise the precedence of ',' operators in the
operands of '? :' in the macro defined above.

Hence, the correct definition would be
#define DIV_MOD(d,r,x,y) ( y == 0.0 ? (d = 0.0, r = x) : (d = x/y, r = x - d*y))

	-	Ravi Mandava

-- 
**********************   #include <stddisclaimer.h>  **************************
Ravi Mandava			e-mail :	ravim@gtenmc.gtetele.com
					  or    ravim@gtenmc.UUCP
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