Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!bu-cs!purdue!i.cc.purdue.edu!h.cc.purdue.edu!ags
From: ags@h.cc.purdue.edu (Dave Seaman)
Newsgroups: comp.lang.fortran
Subject: Re: i++, i+=1, i=i+1
Message-ID: <3976@h.cc.purdue.edu>
Date: 15 Sep 88 22:01:56 GMT
References: <13566@mimsy.UUCP> <3629@lanl.gov>
Reply-To: ags@h.cc.purdue.edu.UUCP (Dave Seaman)
Organization: Purdue University
Lines: 23

In article <3629@lanl.gov> jlg@lanl.gov (Jim Giles) writes:
>My english description of 'i = i + 1' _is_ "add 1 to i".  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.  It need
>only look for '+='  and replace it with '= _X_' where _X_ is whatever
>token preceeds the '+='.  In other words, as far as functionality
>goes, '+=" doesn't do a damn thing.

If you apply your preprocessor to 

	x[i*f(j)+k*g(l)] += y

you get

	x[i*f(j)+k*g(l)] = x[i*f(j)+k*g(l)] + y

which is not the same expression at all, becauses it causes the the subscript 
to be evaluated twice.

-- 
Dave Seaman	  					
ags@j.cc.purdue.edu