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From: firth@sei.cmu.edu (Robert Firth)
Subject: Re: "Subtract C, add Ada"
Message-ID: <1995Jan23.154631.6702@sei.cmu.edu>
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References: <3fo2ot$su2@miranda.gmrc.gecm.com>
Date: Mon, 23 Jan 1995 15:46:31 EST
Date: 1995-01-23T15:46:31-05:00
List-Id: <comp.lang.ada>

In article <3fo2ot$su2@miranda.gmrc.gecm.com> bill@valiant (R.A.L Williams) writes:

I guess I'm about to show my ignorance of C, but I'm very confused
bt this post.

> 1. It allows your code to be more compact.

>    NB DONT confuse compactness with poor layout! I find that, for example:
>
>       while ((c = getchar()) == ' ')
>       {
>          /* count spaces */
>       }
>
>    is clearer than the 'expanded' alternative (to *me* :-).

Nope, I find this totally unclear.  Who's counting?  Unless I've missed
an invisible declaration, initialisation, and increment, the above
code *doesn't* count spaces, it skips them.  And if that is its
purpose, what's the point of the variable 'c'?  Why not just say

	WHILE getchar = ASCII.SP LOOP null; END LOOP;

Though, again, I'd much rather write this:

	LOOP
	   get(c);
	   EXIT WHEN c /= ASCII.SP;
	END LOOP;

since the postcondition I almost certainly want to establish - that
c holds the next non-space character - is written right there in the code.

Note also that if there are *no more* non space characters, the C code
dies in an infinite loop, while the Ada code automatically does the
right thing, namely raises the END_ERROR exception.

>OK, its no big thing to write:
>
>    P(I) := Q(I);
>    I := I + 1;
>
>instead of
> 
>    *p++ = *q++;
>
>but I actually *do* find the C representation easier/better etc. (perhaps
>I'm wierd?)

Again, I don't see it.  The Ada code makes it clear that *corresponding*
elements of the array Q are being copied into P - though, of course,
a real Ada programmer (TM) would have written just P := Q.  The C code
doesn't make that clear - you're going to have to ferret out the
initialisations of p and q to determine that.  And if you worry about
the correctness of the copy - for instance, whether P and Q are the
same size - that's surely going to be a lot easier to establish in Ada.