Path: utzoo!attcan!uunet!samsung!uakari.primate.wisc.edu!ames!haven!umd5!crabcake!zhu
From: zhu@crabcake.cs.jhu.edu (Benjamin Zhu)
Newsgroups: comp.lang.c
Subject: Re: () ignored in some expressions
Message-ID: <1380@crabcake>
Date: 13 Apr 90 05:35:11 GMT
References: <48079@lanl.gov> <1272@sdrc.UUCP> <41297@ism780c.isc.com>
Reply-To: zhu@crabcake.cs.jhu.edu (Benjamin Zhu)
Followup-To: comp.lang.c
Organization: Johns Hopkins University CS Dept -- Town of Solitude
Lines: 40
Keywords:

In article <41297@ism780c.isc.com> marv@ism780.UUCP (Marvin Rubenstein) writes:
>In article <1272@sdrc.UUCP> scjones@sdrc.UUCP (Larry Jones) writes:
>>In article <48079@lanl.gov>, u096000@lanl.gov (Roger A. Cole) writes:
>>> In K&R1, expressions involving one of the associative and commutative
>>> operators can be arranged even when parenthesized.
>>
>>Well, if the operators ARE commutative and associative, it
>>doesn't make any difference!  In the environment the C grew up
>>in, integer arithmetic overflows wrap around without producing
>>any exceptions, so the integer operators really are associative
>>and commutative.
>
>A common misconception.  Integer operators are associaive for add and
						^^^^^^^^^^^^^^^^^^^^^^
>subtract but not for multiply and divide.  for example:
 ^^^^^^^^

Oh, really? How about 1-2+3-4, 1-(2+3)-4, ...
Well, you can enumerate all of the combinations. Are the results all 0?
I am confused.

Strictly speaking, the integer operations are associative only if a single
operator is involved.  Otherwise, you could never tell.

Sigh, algebra is still useful.

>
>    long x=70000;
>    x*(x/x);   /* 700000 if parens are honored */
>    (x*x)/x;   /* 8643   if parens are honered */
>
>The above assumes longs are 32 bits.
>
>    Marv Rubinstein


Benjamin Zhu
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Sorry, but I have no disclaimer for you this time.
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