/*  File: fptr1.c

    Exploring function pointers.
*/

#include <stdio.h>

/* some simple functions */

int add3(int n) {
   return n + 3 ;
}

int add5(int n) {
   return n + 5 ;
}


/* Takes a function parameter */

int apply (int addx(int), int m) {
   return addx(m) ;
}

main() {
   int m = 2, result ; 

   /* fptr is a variable that holds the address of a function
      which takes an int parameter and returns an int.
   */
   int (*fptr)(int) ;

   printf("m + 3 = %d \n", add3(m) ) ;
   printf("m + 5 = %d \n", add5(m) ) ;
   printf("\n") ;

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

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

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

   result = (*fptr) (10) ; /* function application has higher precedence */
   printf("Applying fptr to 10, result = %d\n", result) ; 
}