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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: C history question
Keywords: C design, XOR
Message-ID: <19510@mimsy.UUCP>
Date: 11 Sep 89 17:37:04 GMT
References: <575@calmasd.Prime.COM>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 24

In article <575@calmasd.Prime.COM> wlp@calmasd.Prime.COM (Walter Peterson)
writes:
>C has bitwise operators for AND (&), OR (|) and XOR (^) and boolean 
>operator for AND (&&) and OR (||), but not for XOR (^^). Why?

The best explanation I have ever heard is that the important property
of && and || is not their `booleanness', but rather that they are
short-circuit operators (they avoid evaluating the right hand side
whenever the left hand side gives the answer by itself).  By definition,
exclusive or cannot short circuit, so the `^^' operator would be
misleading.

>... why make people go to the trouble of writing something like
>(a || b) && (!(a && b)) when a ^^ b is so much "cleaner".

The simplest expression for `boolean xor' is

	!a != !b

since `!' is a boolean-normalising `not' operator and inverted
inputs to xor still yeild xor.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris