Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!decwrl!megatest!djones
From: djones@megatest.UUCP (Dave Jones)
Newsgroups: comp.lang.c
Subject: Re: `if (a = b)' (was Standard indentation?)
Message-ID: <1071@goofy.megatest.UUCP>
Date: 13 Dec 88 00:54:07 GMT
References: <5@rsoft.UUCP>
Organization: Megatest Corporation, San Jose, Ca
Lines: 45

There is a construct that is a little awkward using standard
(Pascal-like) structured statements:  You want to read a value
from an external source, exit the loop if the value is a sentinal,
or process the value and continue if not a sentinal.

{
  int ch;
  do
    { 
      ch = getchar();
      if(ch != EOF) process(ch);
    } 
  while (ch != EOF);
}


The expression !EOF gets evaluated twice.  A compiler that
does common subexpression-removal and global flow-analysis 
would fix things, but not all compilers are that smart.  
Besides, I'm one of those old fashioned guys who wants the
compiler to do what I say. Or rather, I would like to be able 
to say what I really want the compiler to do.

So we could do this:

for(;;)
  {
     int ch = getchar();
     if(ch == EOF) break;
     process(ch);
  }

This is nice, in as much as it moves the declaration of ch one
level deeper.  But it has the somewhat unstructured "break".
Still, not too bad.  I prefer the following:


{ int ch;
  while( (ch = getchar()) != EOF )
    process(ch);
}


This says it almost literally,  "While I get a ch that is not 
a sentinal, I want to continue processing."