Path: utzoo!mnetor!uunet!husc6!mit-eddie!ll-xn!ames!nrl-cmf!cmcl2!brl-adm!adm!cantrell@arecibo.aero.ORG
From: cantrell@arecibo.aero.ORG (JOHN CANTRELL)
Newsgroups: comp.lang.pascal
Subject: RE: Global variables
Message-ID: <12633@brl-adm.ARPA>
Date: 25 Mar 88 12:31:57 GMT
Sender: news@brl-adm.ARPA
Lines: 59

I can't speak for Borland (maybe somebody in netland will), but I can
speak from experience in the DoD software area.  Seen from here, there
are several shortcomings with declaring everything global.  For example:

1. Global variables exist (i.e., they hold space) as long as 
   the program does, locals go away when the procedure is done. 
   Sure, you say, memory is cheap, I can always buy another megabyte.  
   For every megabyte you add, there is some programmer waiting to use it. 
   There are ways to get around this, but why should you, Pascal has
   local variables for this purpose, so why not make use of the 
   facilities of the language.

2. If you have a big project (500,000 lines, 40 programmers), how are
   you going to keep the names straight? Try using i, j and k as loop 
   counters where a subroutine or two is called inside a loop.  If these are
   global, you are guaranteed to have trouble.  And no matter how many loop
   counters you declare globally, I will bet my last dollar that some
   hacker on the project will need 'just one more'.

3. Let's just say that you do declare everything global.  Your names
   may not make much sense to the other programmers on the job, but so
   what, they shouldn't be using your variables anyway.  Then you get
   some new guy on the job finishing up for someone else who left and
   this guy makes the mistake of using one of YOUR variables.  How are
   you going to debug the program when you put everything together later?
   (This is my pet peeve -- I was in testing!)  I tell you how it's done
   now:  You unit test your little piece, then hand it over to the 
   testing organization and get yourself a new job on a new project.  Oh,
   yes, DON'T ever leave a phone number, either, those testing weenies
   will bother the heck out of you with questions when the code is as
   plain as the nose on their face.

Now, just let me get down off the soapbox . . .
So, there really are uses for local declarations.  CMU is probably trying
to get you ready for the great big world out here where all projects are 
NOT one-man jobs.  The best advice: Let them show you the way, but then
reserve judgement until you have worked on a project with 40 other 
programmers -- or better yet, until you have TESTED the work of some 40
programmers.  Then you might get an idea of what they are trying to put
across to you at CMU.

Hope this helps a little.

		-jc

                                John C. Cantrell
                           The Aerospace Corporation
                        2350 East El Segundo Boulevard
                          El Segundo, CA 90245-4691
                             Tel: (213) 336-4333
                          cantrell@arecibo.aero.org
 
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