Official Fortran standards

[Toon Moene]

Robert Dewar wrote:

> > Well, the Fortran77 standard states:
> >         When a DO-loop becomes inactive, the DO-varible of the DO-loop
> >         retains its last defined value.
> >
> > So you get the current value if you jump out of the loop, or the next
> > value (one increment greater than last) if you fall thru.

> The last defined value could only mean the value the last time through the
> loop. It certainly cannot be one greater since the loop might have an upper
> bound equal to the highest allowed integer value.

Hmmm, I don't think this is correct.

Quoting http://www.fortran.com/F77-std/rjcnf-11.html#sh-11.10.7:

"Incrementation processing has the effect of the following steps
performed in sequence: 

    1.The DO-variable, the iteration count, and the incrementation 
      parameter of the active DO-loop whose DO statement was most
recently 
      executed, are selected for processing. 
    2.The value of the DO-variable is incremented by the value of the 
      incrementation parameter m3. 
    3.The iteration count is decremented by one. 
    4.Execution continues with loop control processing (11.10.4) of the 
      same DO-loop whose iteration count was decremented."

IOW, the DO-variable is incremented before the decision whther the loop
should be terminated is taking.

This is confirmed by the examples given in the Fortran 77 standard:

"For example: 

      N=0
      DO 100 I=1,10
      J=I
      DO 100 K=1,5
      L=K
  100 N=N+1
  101 CONTINUE

After execution of these statements and at the execution of the CONTINUE
statement, I=11, J=10, K=6, L=5, and N=50."

Note the value of I.

-- 
Toon Moene - mailto:toon@moene.indiv.nluug.nl - phoneto: +31 346 214290
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