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From: drw@cullvax.UUCP (Dale Worley)
Newsgroups: comp.lang.c
Subject: condition expressions
Message-ID: <1221@cullvax.UUCP>
Date: Wed, 27-May-87 15:00:16 EDT
Article-I.D.: cullvax.1221
Posted: Wed May 27 15:00:16 1987
Date-Received: Sat, 30-May-87 01:54:44 EDT
Organization: Cullinet Software, Westwood, MA, USA
Lines: 36

levy@ttrdc.UUCP (Daniel R. Levy) writes:
> In article <874@cc5.bbn.com.BBN.COM>, keesan@cc5.bbn.com.BBN.COM (Morris M. Keesan) writes:
> < In article <801@rtech.UUCP> daveb@rtech.UUCP (Dave Brower) writes:
> < <What is the type of the result of evaluating:
> < <	(expr) ? (double) x : (char)y
> <  The Draft Proposed American National Standard is even clearer:
> < "If both . . . have arithmetic type, the usual arithmetic conversions are
> < performed to bring them to the same type and the result has that type."
> 
> Well, this quotation says that the "usual arithmetic conversions" are
> performed to bring the expressions to the same type, but it still doesn't
> say WHAT type prevails if the two differ; "usual arithmetic conversions"
> is begging the question!

The type of the result is implicit in the fact that C types that are
used in expression computation fall in a linear order

int : unsigned int : long int : unsigned long int : double

(Under ANSI, float gets stuck in somewhere -- what if float can't
accomodate long int?)

Thus, given two types, one of them is "bigger" - that's the one that
the conditional expression returns.  For the example, "char" becomes
"int" automatically, and "double" is bigger than that.

(In general, you don't need a linear order, only a "join semilattice";
given any two types there is a minimum type that is "bigger" than both
of them.)

Dale
-- 
Dale Worley		Cullinet Software
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