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From: steven@mcvax.uucp (Steven Pemberton)
Newsgroups: net.lang.c,net.lang.pascal
Subject: Re: Pascal vs C, again (was: Pascals Origins)
Message-ID: <7018@boring.mcvax.UUCP>
Date: Thu, 24-Jul-86 09:32:41 EDT
Article-I.D.: boring.7018
Posted: Thu Jul 24 09:32:41 1986
Date-Received: Thu, 24-Jul-86 21:45:50 EDT
References: <2222@brl-smoke.ARPA> <7014@boring.mcvax.UUCP> <3130@utcsri.UUCP>
Reply-To: steven@boring.uucp (Steven Pemberton)
Organization: CWI, Amsterdam
Lines: 48
Xref: mnetor net.lang.c:5430 net.lang.pascal:343
Apparently-To: rnews@mcvax


In article <3130@utcsri.UUCP> greg@utcsri.UUCP (Gregory Smith) writes:
> Given     var	x: array [1..1000] of integer;
> write a code fragment to find the location of the first 0 in x. The
> condition that no zeroes exist must be distinguished. Further rules:
> 	- Standard Jensen & Wirth Pascal ( no break from loop )
> 	- *** x[i] must not be evaluated for i<1 or i>1000 ***
> 	- The search loop must be terminated as soon as a zero is found.
> 	- 'a or b', 'a and b' always evaluate both a and b

What I find an elegant solution to this sort of problem is the following:

	var state: (searching, found, absent);
	    i: 1..1000;

	i:=1; state:=searching;
	repeat
	   if x[i]=0 then state:=found
	   else if i=1000 then state:=absent
	   else i:=succ(i)
	until state <> searching;

	case state of
	found: writeln('found at ', i);
	absent:writeln('not there')
	end

I like it because it is explicit and generalisable for searches with more
states. Note that i only takes values in 1..1000 and x[i] is only evaluated
once for each element.

I still think Jack Jansen's main point has been ignored in this discussion:
you run a C program that overruns an array, and it may run to completion, or
at best say "Memory fault - core dumped".

Do the same with a Pascal program, and you're quite likely to get something
like "Index out of bounds at line 123, value = -1". (Actually I just tried
it here, and with "x[1234]:=0", I got a compile-time error! The C version
ran without complaint).

This difference can make a huge difference to the time needed to get a
program running, and the confidence you have in it at the end. This
advantage far outweighs the minor notational inconveniences that this group
seems obsessed with.

Disclaimer: I think that there are programming languages FAR better than
both Pascal and C. However, I try to remain objective about all of them.

Steven Pemberton, CWI, Amsterdam; steven@mcvax.uucp