From: Weiqi Gao <weiqigao AT a DOT crl DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: "for" messages
Date: Mon, 22 Nov 1999 23:49:22 -0600
Organization: CRL Network Services
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Rodeo Red wrote:
> 
> Weiqi Gao wrote:
> 
> > The code in your file used to be legal C++ code, but the final ANSI C++
> > standard made it illegal.
> >
> 
> By "illegal" you mean the program won't compile ? Then these are error messages and
> not just warnings ?  (How does one ultimately tell ?)

Warning messages are flagged as so, as in:
  foo.cc:3: warning: variable 'i' defined but never used

> > The thing to note here is that the scope of a variable declared in the
> > head of a loop is the rest of the head and inside of the braces:
> >
> >   for (/* declare variable here */; /* use it here */ ; /* use it here
> > */) {
> >     /* use it here */
> >   }
> >   /* can't use it here */
> 
> according to what your saying I should add braces to lines 20 and 26- {}
> for example change:

No the braces here are not important.

>  line 19     for (i = 0; i < 5; i++)
> line  20    cout << "num[" << i <<"] == " << num[i] << '\n';
> 
> to [...]
> 
> I thought that shouldnt matter because the i is also declared in the second loop.

Here's the key to your troubles!  You did not declare the 'i' in your
second for() loop:

  for (i = 0; i < 5; i++) {
    // stuff
  }

"i = 0" is an assignment.  For it to be legal, 'i' must have been
declared earlier in the scope.
You can make it a declaration by changing "i = 0" to "int i = 0".

> > The error messages you received from the compiler is an attempt by the
> > gcc authors to help users who know the old rule (which says you CAN use
> > the variable).  Had they been less considerate, you would have received
> > this error message:
> >
> >   testfile.cpp:25: 'i' undeclared (first use in this function)
> 
> OK so they ARE error messages. That makes sense but I still don't understand what
> the fix is.

Change your

  for (int i = 0; i < 5; i++) {
    // stuff
  }

  for (i = 0; i < 5; i++) {
    // stuff
  }

into

  for (int i = 0; i < 5; i++) {
    // stuff
  }

  for (int i = 0; i < 5; i++) {
    // stuff
  }

And mentally realize that the 'i' in the second for() loop has
absolutely nothing to do with the one in the first for() loop.

> Thanks for that clarification anyway.  Onward through the fog!

-- 
Weiqi Gao
weiqigao AT a DOT crl DOT com