declaration or definition

[pgupta0609]

if i write a statement in C/C++..........

main()
{
int x;
}

is this a declaration or definition?

if this is a declaration then why it display garbage value for x?

[Banfa]

That doesn't display any value for x there is no output statement.

It is a definition because it actually causes the compiler to allocate memory space to use for the variable x, however using an automatic scope variabole without initialising it is undefined behaviour.

[donbock]

A declaration says that somewhere there is a variable or function named foo.

A definition says here is a variable or function named foo.

[Dheeraj Joshi]

int x;

is a declaration.

Regards
Dheeraj Joshi

[Banfa]

int x;

is a declaration.

No its a definition, it actually defines the variable, causes the compiler to allocate memory for it.

[donbock]

If the following statement appears in multiple files, then it is a definition in one of them and a declaration in all the others. It can be difficult to predict which instance turns out to be the definition.

extern int x;

I can't think of a way other than extern to create a variable declaration.

I think the confusion comes because many people casually refer to variable declarations. Pedants (I'm not naming any names, but I'm one of them) point out that the C Standard has precise definitions for the terms definition and declaration that differ from casual usage.

It is entirely possible that these precise definitions differ from Standard usage in other languages. That's another source of confusion -- words can change their meaning depending on the context in which they are used.