/*  File: fptr2.c

    Exploring function pointers.
*/

#include <stdio.h>

/* some simple functions */

void add3(int *iptr) {
   *iptr = *iptr + 3 ;
}


void add5(int *iptr) {
   *iptr = *iptr + 5 ;
}


/* Takes a function parameter */

int apply (void addx(int *), int r) {
   
  addx(&r) ;
  return r ;
}

main() {
   int m = 2, result ; 

   /* fptr is a variable that holds the address of a function
      which takes an int pointer parameter and returns nothing.
   */
   void (*fptr)(int *) ;

   add3(&m) ;
   printf("After add3(&m), m = %d\n", m) ;
   add5(&m) ;
   printf("After add5(&m), m = %d\n", m) ;
   printf("\n") ;

   result = apply(&add3, m) ;
   printf("Applying add3 to m, result = %d\n", result) ; 
   printf("m = %d\n", m) ;
   result = apply(&add5, m) ;
   printf("Applying add5 to m, result = %d\n", result) ; 
   printf("m = %d\n", m) ;
   printf("\n") ;

   fptr = &add3 ;
   (*fptr) (&m) ; /* function application has higher precedence */
   printf("Applying fptr to m, m = %d\n", m) ;
}