Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!bionet!ames!hc!lanl!jlg
From: jlg@lanl.gov (Jim Giles)
Newsgroups: comp.lang.fortran
Subject: Re: DO loops, anyone?
Message-ID: <11020@lanl.gov>
Date: 24 Mar 89 01:10:43 GMT
References: <1917@devsys.oakhill.UUCP>
Organization: Los Alamos National Laboratory
Lines: 41

From article <1917@devsys.oakhill.UUCP>, by steve@oakhill.UUCP (steve):
> [...]
> Going back to my code:
> 
>       k = 0
>       do 10 i = 1,10
>        if (i.eq.1.or.i.eq.5) goto 10
>         do 10 j = 1,10
>           if (j.eq.3) goto 10
>    10 k = k + 1
> 
> I assume this puts you in the camp that when i = 1 or i = 5 that
> k is not incremented.  There is a large segment of coders that think
> it should be. [...]

Consider:
       do 10 i = 1,10
        if (i.eq.1.or.i.eq.5) goto 10
         do 10 j = 1,10
    10 array(j)=array(j)+1

This is the same as your loop except for the final statement (your final
IF statement is a no-op and should be eliminated by a smart compiler
anyway).  Here it is quite clear that the array incrementing should _NOT_
be done as a result of the outer loop GOTO - in the first pass the variable
J hasn't even been defined yet!  As I pointed out before, either the
branch should be illegal or the semantics should be:

       k = 0
       do 10a i = 1,10
        if (i.eq.1.or.i.eq.5) goto 10a
         do 10 j = 1,10
           if (j.eq.3) goto 10
    10 k = k + 1
   10a continue

This interpretation is at least consistent and well defined on both 
examples.

J. Giles
Los Alamos