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From: mesmo@Portia.Stanford.EDU (Chris Johnson)
Newsgroups: comp.lang.c
Subject: Re: Another silly question
Message-ID: <2336@Portia.Stanford.EDU>
Date: 17 May 89 20:07:15 GMT
References: <17812@cup.portal.com>
Sender: Chris Johnson <mesmo@Portia.stanford.edu>
Reply-To: mesmo@Portia.Stanford.EDU (Chris Johnson)
Organization: Stanford University
Lines: 20

From article <17812@cup.portal.com>, by Tim_CDC_Roberts@cup.portal.com:
> Ok, folks.  In regards to  "a[i] == *(a+i) == *(i+a) == i[a]", let me
> refer to the oft-used example  2["hello"].
> I agree that this works and is equivalent to "hello"[2].  I've seen it
> in books and postings.  My simple question is why? 

	The supposed proof of a[i] == i[a] rests on the faulty
	assumption that (x+y) == (y+x) in all contexts; this is
	not correct.

	When "+" denotes simple (ie int/float/etc) arithmetic, the
	operation commutes; when it denotes pointer arithmetic,
	commutation is not legal/meaningful.

	The statement that *(a+i) == *(i+a) is therefore invalid.
-- 
==============================================================================
 Chris M Johnson === mesmo@portia.stanford.edu === "Grad school sucks rocks"
            "Imitation is the sincerest form of plagiarism" -- ALF
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