Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!amdahl!pyramid!bgg
From: bgg@pyrps5 (Ben Golding - R+D Australia)
Newsgroups: comp.lang.fortran
Subject: Re: i++, i+=1, i=i+1
Summary: i += 1 and i = i + 1 are *not* purely textual
Message-ID: <39754@pyramid.pyramid.com>
Date: 15 Sep 88 20:39:15 GMT
Sender: daemon@pyramid.pyramid.com
Lines: 24

In article <3629@lanl.gov>, jlg@lanl.gov (Jim Giles) writes:
>							    the difference
> between that and 'i += 1' is purely textual.  It's easy to write a
> preprocessor to switch the later to the former.  Such a preprocessor
> needn't have _any_ semantic knowledge of the target language.

This is nonsense - it is not a "purely textual difference" if there are
side effects.  The "FORTRAN" statements:

	a(icomp(j)) += 1;

and

	a(icomp(j)) = a(icomp(j)) + 1;

are not purely textual substitutions if icomp is a function that
changes the value of j.

This distinction is particularly important in C where "i++" is commonly
used and produces rather different results if the expression is evaluated
twice.

	Ben Golding (bgg@yarra.oz.au)
	Pyramid Technology Corporation (Australia)