Scope rules in C

Last Updated : 17 Oct, 2025

The scope of a variable in C is the block or the region in the program where a variable is declared, defined, and used. Outside this region, we cannot access the variable, and it is treated as an undeclared identifier.

  • The scope of an identifier is the part of the program where the identifier may directly be accessible.
  • All variables are lexically(or statically) scoped in C which means the scope is defined at the compiler time and not dependent on the caller of the function.
C 
#include <stdio.h>

int main()
{
    // Scope of this variable is 
    // within main() function only.
    int var = 34;

    printf("%d", var);
    return 0;
}

// function where we try to access 
// the var defined in main()
void func() { printf("%d", var); }


Output

solution.c: In function 'func':
solution.c:15:28: error: 'var' undeclared (first use in this function)
 void func() { printf("%d", var); }

Here, we tried to access variable names var As we can see that if we try to refer to the variable outside its scope, we get the above error.

Global Scope in C

The global scope refers to the region outside any block or function.

  • The variables declared in the global scope are called global variables.
  • Global variables are visible in every part of the program.
  • Global is also called File Scope as the scope of an identifier starts at the beginning of the file and ends at the end of the file.
C 
#include <stdio.h>
 
// variable declared in global scope
int global = 5;
 
// global variable accessed from
// within a function
void display(){
    printf("%d\n", global);
}

int main(){
    printf("Before change within main: ");
    display();
 
    // changing value of global
    // variable from main function
    printf("After change within main: ");
    global = 10;
    display();
}

Output
Before change within main: 5
After change within main: 10

Linkage of Variables in Global Scope

Global variables have external linkage by default. It means that the variables declared in the global scope can be accessed in another C source file. We have to use the extern keyword for that purpose.

Example of External Linkage

file1.c

C 
// filename: file1.c
#include <stdio.h>

// Define the global variable
int a;

// Define the function to 
// use the global variable
void myfun(){
    printf("%d\n", a);
}


main.c

C 
// filename: main.c
#include <stdio.h>

// Declare the external variable and function
extern int a;
void myfun();

int main(void)
{
    // Initialize the global variable
    a = 2;

    // Call the function to print the value of 'a'
    myfun();

    return 0;
}


Output

2

Note: To restrict access to the current file only, global variables can be marked as static.

Local Scope in C

The local scope refers to the region inside a block or a function. It is the space enclosed between the { } braces.

  • The variables declared within the local scope are called local variables.
  • Local variables are visible in the block they are declared in and other blocks nested inside that block.
  • Local variables have no linkage.
C 
#include <stdio.h>

int main()
{
    {
        int x = 10, y = 20;
        {
            // The outer block contains
            // declaration of x and
            // y, so following statement
            // is valid and prints
            // 10 and 20
            printf("x = %d, y = %d\n", x, y);
            {
                // y is declared again,
                // so outer block y is
                // not accessible in this block
                int y = 40;

                // Changes the outer block
                // variable x to 11
                x++;

                // Changes this block's
                // variable y to 41
                y++;

                printf("x = %d, y = %d\n", x, y);
            }

            // This statement accesses
            // only outer block's
            // variables
            printf("x = %d, y = %d\n", x, y);
        }
    }
    return 0;
}

Output
x = 10, y = 20
x = 11, y = 41
x = 11, y = 20
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