extern keyword: This discussion will be very useful for beginners with C language.

Before going for extern we look at the C variable declaration and definition

Declaration:  Declaration of a variable simply states that the variable exists somewhere in the program in that scope. While memory is not allocated to the variable.

Definition: Definition is the super-set of declaration. Variable definition means that a variable is declared and memory is allocated to that variable.

extern keyword extends the visibility of the C variables and functions throughout the program.

i.e u can define a variable once and use any where in the program with the help of extern.

lets understand with example program

filename: new.c

extern int ll;

void fun()

{

printf("hello=%d\n",ll);

return;

}

filename: prog.c

#include<stdio.h>

#include"new.c"

int ll=10;

void fun();

int main()

{

fun();

return 0;

}

in new.c  we are just referring to variable ll and that can present any where in the program, ll is defined and declared in prog.c

when u run the program get 10 as output.

Now we can call extern int ll as declaration and int ll=10 as definition.

Happy Coding!!!!