Passing of pointers as function parameters

Program 54) Write a function using pointers to exchange the values in tw2o location in the memory.
This program shows how the content of two locations can be exchanged using their address locations. The function exchange ( ) recieves the addresses of the variables x and y exchanges their contents.

                                   PROGRAM

void exchange (int *, int *) ;       /*     prototype       */
main ( )
 {
       int x, y ;
      x = 100 ;
      y = 200 ;
      printf ("Before exchange  : x = %d   y = %d\n\n", x, y) ;
      exchange (&x, &y) ;    /*      call      */
      printf ("After exchange   :  x = %d   y = %d\n\n", x, y) ;
 }
 exchange (int *a, int *b)
 {
         int t ;     /*  Assign the value at address a to t  */
         t = *a ;   /*  put b into a  */
         *a = *b ;   /*  put t into b   */
 }

Output:           Before exchange   :  x = 100   y = 200
                       After exchange      :  x = 200   y = 100


You may note the following points:
1. The function parameters are declared as pointers.
2. The dereferenced pointers are used in the function
    body.
3. When the function is called, the addresses are passed
    as actual arguements.