Illustration of properties of global variables

Program 45) Write a multifunction program to illustrate the properties of global variables.
This program illustrate the properties of global variables. Note that variable x is used in all functions but none except fun2, has a definition for x. Because x has been declared 'above' all the functions, it is available to each function without having to pass x as a function argument. Further, since the value of x is directly available, we need not use return(x) statements in fun1 and fun3. However, since fun2 has a definition of x, it returns its local value of x and therefore uses a return statement. In fun2, the global x is not visible. The local x hides its visibility here.

                                     PROGRAM

int fun1 (void) ;
int fun2 (void) ;
int fun3 (void) ;
int x ;               /*       Global        */
main ( )
 {
       x = 10 ;          /*     Global        */
       printf ("x = %d\n", x) ;
       printf ("x = %d\n", fun1() ) ;
       printf ("x = %d\n", fun2() ) ;
       printf ("x = %d\n", fun3() ) ;
 }
 fun1 (void)
 {
        x = x + 10 ;
 }
 int fun2 (void)
 {
      int x ;      /*  Loacl   */
      x = 1 ;
      return (x) ;
 }
 fun3 (void)
 {
      x = x + 10 ;    /*  Global   */
 }

Output:           X = 10
                        X = 20
                        X = 1
                        X = 30

Once a variable has been declared as global, any function can use it and change its value. Then, subsequent functions can reference only that new value.