Xref: utzoo comp.lang.modula2:1259 comp.lang.c:16047
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!decwrl!labrea!polya!Polya.Stanford.EDU
From: crew@Polya.Stanford.EDU (Roger Crew)
Newsgroups: comp.lang.modula2,comp.lang.c
Subject: Re: "for" loops (was Re: C++ vs. Modula2)
Message-ID: <6680@polya.Stanford.EDU>
Date: 6 Feb 89 18:39:31 GMT
References: <19579@agate.BERKELEY.EDU> <8515@lanl.gov> <6419@polya.Stanford.EDU> <1004@ubu.warwick.UUCP>
Sender: crew@polya.Stanford.EDU
Reply-To: crew@Polya.Stanford.EDU (Roger Crew)
Followup-To: comp.lang.modula2
Organization: Stanford University Computer Science Dept.
Lines: 51
In-reply-to: geoff@warwick.UUCP (Geoff Rimmer)

In article <1004@ubu.warwick.UUCP>, geoff@warwick (Geoff Rimmer) writes:
> In article <6419@polya.Stanford.EDU> crew@Polya.Stanford.EDU (Roger Crew) writes:
> >Here's a quiz:
> >How would you write the following in C?
> >
> >	VAR a, b, c : Char;
> >	...
> >	FOR c = a TO b DO ... END;
> >
     [ ... yup, this discussion ...]
>
> What a stupid question.  If you are going to count from 0 to 255, you
> wouldn't use char in the first place - you'd use unsigned char, or
> int.  I can't see what you're getting at, at all.

I'll grant that, for the benefit of compilers that *have* signed
chars, I actually did intend to say ``unsigned char'' rather than
``char''.  The fact of the matter is, however, that

        unsigned char a;
	for( c=0; c<=255; ++c) {...}

still doesn't work.  You can try it if you like, or you can read the
submissions from the other 10 posters who understand what's going on...  

The fact that I was using chars signed or unsigned is irrelevant to
the point I was trying to make, namely that the semantics of C
for-loops and Modula/Pascal for-loops are entirely different -- it is
not simply a case of one being more general than the other.  While
it's fairly obvious that a general C for-loop often can't be written
as a Modula for-loop, it's not so obvious (or at least, *I* didn't think
it was completely obvious...) that to do a general Modula for-loop
in C *also* requires strange contortions.

As for *why* I'd want to be counting with chars, just consider any
application requiring some kind of array indexed by chars, e.g.,

	VAR font : ARRAY Char OF Bitmap;

It's an obvious thing to do in Modula.  I suppose this also
illustrates the danger of carrying over one languages way of thinking
into another, a problem that does not confine itself to for-loops.

> Go back to writing Fortran.  Let the *real* programmers use C. :-)

I'll let this statement speak for itself.  :=)

--
Roger Crew					``Beam Wesley into the sun!''
Usenet:    {arpa gateways, decwrl, uunet, rutgers}!polya.stanford.edu!crew
Internet:  crew@polya.Stanford.EDU