Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!uw-june!uw-entropy!mica!charlie
From: charlie@mica.stat.washington.edu (Charlie Geyer)
Newsgroups: comp.lang.fortran
Subject: Re: DO loops, anyone?
Message-ID: <1317@uw-entropy.ms.washington.edu>
Date: 16 Mar 89 02:20:09 GMT
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In article <6667@ecsvax.UUCP> urjlew@ecsvax.UUCP (Rostyk Lewyckyj) writes:
 
> The problem is that the standard allows a code construction that
> easily leads to misuse and stepping over the legal limits. I.e.
> the standard permits a DO loop to end with non trivial executable
> statements (eg  k=k+1 rather than continue or enddo) and it allows
> the closure of multiple DO loops on one statement. 
> The defensive/safety minded programmer can easily avoid the problem 
> by liberal use of CONTINUE statements to remove ambiguities.
> I think that the rational solution is to amend the standard (put it
> in 8x or 9x if 8x never makes it) to require DO loops to be terminated
> one at a time with CONTINUE or ENDDO statements.
> I realize that this will require modifying old source.

A simpler solution would have compilers do run-time error checking and
not jump into inactive loops.  The beauty of this solution is that it
does not not slow down structured code -- no checking necessary.

Unstructured code would take a performance hit.  Serves it right :-)

It's not failure to end every loop with its own CONTINUE that is the
problem.  It is (surprise!) GOTO's are harmful.