External storage class

External variables are differ from remaining other variables. The main features of external variables as following :

Storage	Memory
Keyword	extern
Default initial value	Zero
Scope	Global
Life	As long as the program's execution doesn't come to an end.

External variables are declared outside all functions, yet are available to all functions that care to use them.
Example of external variable or Global variable as following:


/*external variable example program*/
#include<stdio.h>
void add();
void subt();
int main()
{
  printf("\ni=%d",i);
  add();
  add();
  subt();
  subt();
  return 0;
}
void add()
{
  int i;
  i=i+1;
  printf("\nAdding i = %d",i);
}
void subt()
{
  int i;
  i=i-1;
  printf("\nSubtracting i = %d",i);
}


OUTPUT:-


Adding i= 1
Adding i = 2
Subtracting i = 1
Subtracting i = 0


/*program for global variable*/

#include<stdio.h>
int i=50;
void show();
int main()
{
  int i=100;
  printf("\n%d",i);
  show();
  return 0;
}
void show()
{
  printf("\n%d",i);
}


OUTPUT:-


100
50


/*Another example of external or global variable*/

#include<stdio.h>
int i=5;
int main()
{
  extern int j;
  printf("\ni=%d \nj=%d",i,j);
  int j=10;
  return 0;
}


OUTPUT:-


i=5
j=10


Explanation: Because both variables i and j are enjoy as global variable.


You might also like to read : 

1. What is storage classes
2. Automatic storage class
3. Register  storage class
4. Static  storage class
5. Comparison of  storage classes