The scope of an identifier determines the region of a C program in which that identifier can be accessed. Scope depends on where the identifier is declared.

#include <stdio.h>

int global = 10;

int main()
{
    int local = 20;

    if (local > 0)
    {
        int inner = 30;

        printf("global = %d\n", global);
        printf("local = %d\n", local);
        printf("inner = %d\n", inner);
    }

    printf("local = %d\n", local);

    return 0;
}

Example Output #

global = 10
local = 20
inner = 30
local = 20

Explanation #

global is declared outside all functions:

int global = 10;

Its identifier has file scope, so it can be referenced from its declaration to the end of the source file, subject to linkage.

local is declared inside main():

int local = 20;

Its identifier has block scope, so it can be accessed within the block belonging to main() and its nested blocks.

inner is declared inside the if block:

int inner = 30;

Its scope is limited to that block. It cannot be accessed after the closing brace of the if block.

Scope Types #

Nested Block Scope #

An inner block can access identifiers declared in an enclosing block:

int a = 10;

{
    int b = 20;

    printf("%d\n", a);
    printf("%d\n", b);
}

Here, b is accessible only inside the inner block, while a is accessible from both the outer and inner blocks.

Scope determines where an identifier is visible. It does not by itself determine how long the associated object exists; storage duration determines the object’s lifetime.