Scope Rules In C

A scope in any program is a that region of the program where a defined variable can have its existence and beyond that variable can't be accessed. The three places where variables can be declared in C programming language:

C Programming

Local Variables:

Variables which are declared within a function or block are called local variables. They can be used only by statements which are inside that function.Local Variables are not more alive outside the functions .Here is the example of local variables. All the variables a, b and c are local Variables to main() function.

#include <stdio.h>

int main ()

{

/* local variable declaration */

int a, b;

int c;

/* actual initialization */

a = 10;

b = 20;

c = a + b;

printf ("value of a = %d, b = %d and c = %d\n", a, b, c);

return 0;

}

Global Variables:

Global variables are defined outside of all function, used in a program.Global Variables are usually on top of the program. The global variables can be accessed inside any of the functions.You can access them form any where .

Example of global variable is:

#include <stdio.h>

/* global variable declaration */

int g;

int main ()

{

/* local variable declaration */

int a, b;

/* actual initialization */

a = 10;

b = 20;

g = a + b;

printf ("value of a = %d, b = %d and g = %d\n", a, b, g);

return 0;

}

A same name will be assigned to a local and global variables in a same C program but value of local variable inside a function will take preference.

#include <stdio.h>

/* global variable declaration */

int g = 20;

int main ()

{

/* local variable declaration */

int g = 10;

printf ("value of g = %d\n", g);

return 0;

}

Output:

value of g = 10

Formal Parameters:

Function parameters, formal parameters, are treated as local variables inside that function and they will take preference over the global variables.

example:

#include <stdio.h>

/* global variable declaration */

int a = 20;

int main ()

{

/* local variables in main function */

int x= 10;

int y = 20;

int z = 0;

printf ("value of x in main = %d\n", x);

c = sum( x, y);