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.

[Keith Thompson]

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

Peter Nilsson <ai***@acay.com .auwrites:

>Richard<rgr... @gmail.comwrote :

>>vipps...@gmai l.com writes:
mdh wrote:
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?

yes.

Wrong.

No, it isn't.

Wrong.

Whichever way you look at it i is set to the value 0. In programming
this is known as assignment. And I dont see any reason to confuse a
noob by saying any different.

Of course I am trying to use natural English and not be too clever for
my own good.

The C language distinguishes between "initialization " and
"assignment ". I apparently have a higher opinion of mdh's
intelligence than you do; I don't think he'll have any trouble
understanding the distinction.

If you call them both "assignment ", it just makes it more difficult to
explain why one is allowed outside functions and the other is not --
which is exactly what we're discussing in this thread.

We didn't just make up these terms for the fun of it, and they
certainly weren't invented with the intention of confusing people.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[August Karlstrom]

Richard wrote:

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

>Richard Heathfield wrote:

>>mdh said:

[...]

>>>i=0;
That's an assignment statement, which counts as code. You can't have
code outside a function.

Wouldn't it be more accurate to say "you can't have *statements*
outside a function?" To me, "code" could be anything.
August

and "int i=0;" is not a statement now?

It is a declaration as far as I am concerned. If I'm not mistaken a
global declaration like

int i = 0;

does not make the compiler generate instructions for an assignment, the
compiler just makes sure the initial value of i is zero.
August

[Keith Thompson]

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

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

>Richard Heathfield wrote:

>>mdh said:

[...]

>>>i=0;

That's an assignment statement, which counts as code. You can't have
code outside a function.

Wouldn't it be more accurate to say "you can't have *statements*
outside a function?" To me, "code" could be anything.

and "int i=0;" is not a statement now?

No, it's not a statement. It's a declaration.

Words have meanings. If you don't know what a word means, look it up.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[August Karlstrom]

Richard wrote:
[...]

Whichever way you look at it i is set to the value 0. In programming
this is known as assignment.

Believe it or not but some programming languages don't even have assignment.
August

[Richard]

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

Richard wrote:

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

>>Richard Heathfield wrote:
mdh said:
[...]
i=0;
That's an assignment statement, which counts as code. You can't have
code outside a function.
Wouldn't it be more accurate to say "you can't have *statements*
outside a function?" To me, "code" could be anything.
August

and "int i=0;" is not a statement now?

It is a declaration as far as I am concerned. If I'm not mistaken a
global declaration like

int i = 0;

does not make the compiler generate instructions for an assignment,
the compiler just makes sure the initial value of i is zero.

The workings of the underlying compiler are immaterial.

>

August

--

[Richard]

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

Richard wrote:
[...]

>Whichever way you look at it i is set to the value 0. In programming
this is known as assignment.

Believe it or not but some programming languages don't even have assignment.
August

That nice. And I have no reason to disbelieve you. But what that has to
do with this I dont know. Would you like me to list some 68k or Z80 op
codes? But in the context of C it takes a very special person to "not
understand" when I say:

"Whichever way you look at it i is set to the value 0. In programming
this is known as assignment."

or

"At program initialisation the global variable i is assigned the value
0"

I'm not arguing against the standard. I'm not arguing about being
correct. I am arguing for some common sense here. using this word does
not suddenly make some program C "wrong". Hell it wont even compile to
"assign to i" outside of the declaration or the function for crying out
loud.

[August Karlstrom]

Richard wrote:

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

>Richard wrote:

[...]

>>and "int i=0;" is not a statement now?

It is a declaration as far as I am concerned. If I'm not mistaken a
global declaration like

int i = 0;

does not make the compiler generate instructions for an assignment,
the compiler just makes sure the initial value of i is zero.

The workings of the underlying compiler are immaterial.

Just trying to explain the difference between a declaration and a
statement. How a (typical) compiler deals with the two is a part of the
explanation.
August

[August Karlstrom]

Richard wrote:

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

>Richard wrote:
[...]

>>Whichever way you look at it i is set to the value 0. In programming
this is known as assignment.

Believe it or not but some programming languages don't even have assignment.
August

That nice. And I have no reason to disbelieve you. But what that has to
do with this I dont know.

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

[Richard]

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

Richard wrote:

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

>>Richard wrote:
[...]
Whichever way you look at it i is set to the value 0. In programming
this is known as assignment.
Believe it or not but some programming languages don't even have assignment.
August

That nice. And I have no reason to disbelieve you. But what that has to
do with this I dont know.

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

You snipped my "plain english" explanation for some reason.

Where I suggested that saying that "At program initialisation the global variable i is assigned the value
0" is perfectly clear.

Tell me, hand on your heart, are you really trying to tell that makes
"no sense" when explaining to a new programmer what "int i=0;" means
outside of a function?

[Bartc]

"Richard" <rg****@gmail.c omwrote in message
news:gb******** **@registered.m otzarella.org.. .

How the hell is "int i=0;" not code?!?!?!

Why is it so "bad" to say 0 is assigned to i at program initialisation?

It's not executable code (assuming i is outside a function or is static)

In fact int i=0 may not even reserve any actual space in the executable,
while int i=1 probably would.

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.
--
Bartc