A very **very** basic question

[mdh]

As I begin to write more little programs without the help of the
exercises, little things pop up that I need to understand more fully.
Thus, below, and although this is not the exact code, the principle of
the question is the same, ( I hope :-) )
#include <stdio.h>
int i = 0;
int main () { return 0; } /* no errors or warnings*/

but

#include <stdio.h>
int i ;
i=0;
int main () { return 0; } /* 2 warnings. */
I think one of the regular contributors has previously alluded to this
issue, but I wish to understand the principle more clearly.

So, ???

1) int i = 0 is allowed because i is declared and initialized as an
ext variable.
2) int i; i = 0 is not allowed because ?

a) even though my intention is to assign '0' to i , this can only
occur within a function?
b) the compiler thinks I am once again declaring 'i', which has
previously been declared, even though my **intent** is to initialize
an external variable.

I assume the same principles would apply if declared i as "static".

What key principle am I missing.

Thank you as usual.

[Kenny McCormack]

In article <Sb************ *******@text.ne ws.virginmedia. com>,
Bartc <[e-mail] rote:
....

>Writing the explicit assignment i=0 however, would probably generate some
executable code.

Compilers of course can implement these as they like, but I think the
behaviour above is typical.

But such speculation/discussion is, of course, off-topic, since we are
supposed to remain completely oblivious to such things (messy details).

[Old Wolf]

On Sep 26, 8:37*pm, gaze...@shell.x mission.com (Kenny McCormack)
wrote:

In article <d8055424-e34e-4169-8429-d405fa01c...@b2 g2000prf.google groups.com>,

lovecreatesbea. [e-mail] <lovecreatesbea [e-mail] ote:

On Sep 26, 2:47 pm, Keith Thompson <[e-mail] rote:

Right, the standard forbids it because the standard forbids it. *But
the standard doesn't exist in a vacuum, and understanding *why* the
rules are as they are can be useful.

Yes :)

But (again), we're not allowed to think about such things ("why" questions)
here.

Why?

[Nick Keighley]

On 26 Sep, 10:01, Old Wolf <oldw...@inspir e.net.nzwrote:

On Sep 26, 8:37*pm, gaze...@shell.x mission.com (Kenny McCormack)
wrote:

In article <d8055424-e34e-4169-8429-d405fa01c...@b2 g2000prf.google groups.com>,
lovecreatesbea. [e-mail] <lovecreatesbea [e-mail] ote:

>On Sep 26, 2:47 pm, Keith Thompson <[e-mail] rote:

>Right, the standard forbids it because the standard forbids it. *But
>the standard doesn't exist in a vacuum, and understanding *why* the
>rules are as they are can be useful.

>Yes :)

But (again), we're not allowed to think about such things ("why" questions)
here.

Why?

Kenny is trolling

[August Karlstrom]

Keith Thompson wrote:

August Karlstrom <fu********@gma il.comwrites:

>There is a fundamental difference between assignment and [compile
time] initialization (as I tried to explain in a different posting in
this thread).

But the distinction between assignment and initialization isn't a
run-time vs. compile-time distinction.

As far as I know, in C compile-time initialization can only be applied
to variables declared outside a function. If that is the case I consider
my statement above to be correct.
August

[Ben Bacarisse]

Richard<rg****@ gmail.comwrites :

mdh <md**@comcast.n etwrites:

>On Sep 25, 4:17Â*pm, Keith Thompson <[e-mail] rote:

>>>
The C language distinguishes between "initialization " and
"assignment ".

Yes. But we are not compilers.

And to say "0 is assigned to global i at program initialization" is not
exactly going to break the bank.

I would not object to that wording but I would try to avoid in
teaching. The things that can go on the right of the = in an
initialisation are quite different to the things that can go there in
an assignment, so I would want to stress the distinction as soon a
possible since it is not a difficult point. If it were in some way
very complex, I might want to simplify and then expand later, but I
don't think this is the case here.

Initialisations give an initial value to an object through a mechanism
that is quite different to assignment despite the similarity when the
object is not an aggregate.

If you go on to learn other languages, the distinction is even greater
and that can be an important factor when teaching a first language.

--
Ben.

[Eric Sosman]

August Karlstrom wrote:

Keith Thompson wrote:

>August Karlstrom <fu********@gma il.comwrites:

>>There is a fundamental difference between assignment and [compile
time] initialization (as I tried to explain in a different posting in
this thread).

But the distinction between assignment and initialization isn't a
run-time vs. compile-time distinction.

As far as I know, in C compile-time initialization can only be applied
to variables declared outside a function. If that is the case I consider
my statement above to be correct.

#include <stdio.h>
int main(void) {
static char hello[] = "Hello, world!";
puts (hello);
return 0;
}

It's impossible to say whether the initialization of hello[] actually
occurs at compile time, but we do know it occurs before main() begins
to execute.

--
Er*********@sun .com

[August Karlstrom]

Eric Sosman wrote:

August Karlstrom wrote:

>Keith Thompson wrote:

>>August Karlstrom <fu********@gma il.comwrites:
There is a fundamental difference between assignment and [compile
time] initialization (as I tried to explain in a different posting in
this thread).

But the distinction between assignment and initialization isn't a
run-time vs. compile-time distinction.

As far as I know, in C compile-time initialization can only be applied
to variables declared outside a function. If that is the case I
consider my statement above to be correct.

#include <stdio.h>
int main(void) {
static char hello[] = "Hello, world!";
puts (hello);
return 0;
}

It's impossible to say whether the initialization of hello[] actually
occurs at compile time, but we do know it occurs before main() begins
to execute.

OK, you got me. I should change "compile-time initialization" to
"initializa tion of variables with static extent."
August