//  File: fptr2.C
//
//  Exploring function pointers.

#include <iostream.h>
#include <iomanip.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) ;
   cout << "After add3(&m), m = " << m << endl ;
   add5(&m) ;
   cout << "After add5(&m), m = " << m << endl ;
   cout << endl ;

   result = apply(&add3, m) ;
   cout << "Applying add3 to m, result = " << result << endl ; 
   cout << "m = " << m << endl ;
   result = apply(&add5, m) ;
   cout << "Applying add5 to m, result = " << result << endl ; 
   cout << "m = " << m << endl ;
   cout << endl ;

   fptr = &add3 ;
   (*fptr) (&m) ; // function application has higher precedence
   cout << "Applying fptr to m, m = " << m << endl ;
}