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Path: utzoo!mnetor!seismo!rutgers!princeton!allegra!alice!ark
From: ark@alice.UUCP
Newsgroups: comp.lang.c
Subject: Re: Writing readable code
Message-ID: <7056@alice.UUCP>
Date: Sat, 4-Jul-87 11:11:02 EDT
Article-I.D.: alice.7056
Posted: Sat Jul  4 11:11:02 1987
Date-Received: Sat, 4-Jul-87 20:25:59 EDT
References: <1158@copper.TEK.COM> <6858@auspyr.UUCP> <17171@cca.CCA.COM> <262@auvax.UUCP>
Organization: AT&T Bell Laboratories, Liberty Corner NJ
Lines: 40

In article <262@auvax.UUCP>, rwa@auvax.UUCP writes:
> what is the value of x in this fragment:
> 
> 	float x;
> 	int i;
> 
> 	x = 2.0 + ( i = 3.5 );
> 
> I would say 5.5; others might say 5.0, it seems.  But if I _wanted_
> 5.0, I would expect to write
> 
> 	x = 2.0 + (int) ( i = 3.5 );
> 
> and I appeal to the principle of least astonishment for justification.

Ah yes, what should be the value of an assignment? The LHS or the
RHS?  Both answers have their pitfalls, and C says the correct
answer is (a copy of) the LHS.  Thus the answer in your example
is 5.0.  While this produces a surprise in your particular case,
consider:

	double d, a, sqrt();
	d = 2;
	a = sqrt(d);
	a = sqrt(d=2);

Now, don't you want the second and third assignment above to do
the same thing?

In APL, the value of an assignment is the value of its right-hand side.
This mostly works well, but leads to some surprises too:

	A <- 0 0 0 0 0
	B <- A[2 3 4] <- 6
	B <- A[2 3 4]

The first line sets A to a five-element array, all of whose
elements are zero.  The second line sets A[2], A[3], and A[4]
to 6, and also sets B to 6.  The third line sets B to a three-
element array whose elements are all 6.