/*------------------------------------------------------------------*/
/* fnpointers.c (Function pointers)                                 */
/*------------------------------------------------------------------*/

#include <stdio.h>

/*------------------------------------------------------------------*/

static int sqr(int i)

/* Return i squared. */

{
   return i * i;
}

/*------------------------------------------------------------------*/

int main(void)

/* Demonstrate function pointers. */

{
   int i;

   int (*pf)(int);  /* pf is a function pointer.
                       pf is a variable which, when dereferenced, 
                       yields a function that takes an int and 
                       returns an int. */

   /* An ordinary function call: */
   
   i = sqr(5);
   printf("%d\n", i);

   /* A function call through a function pointer: */
   
   pf = sqr;
   i = (*pf)(5);
   printf("%d\n", i);

   /* Unusual ways of using function pointers: */

   pf = &sqr;
   i = (*pf)(5);
   printf("%d\n", i);

   pf = *sqr;
   i = (*pf)(5);
   printf("%d\n", i);

   pf = sqr;
   i = pf(5);
   printf("%d\n", i);

   pf = &sqr;
   i = pf(5);
   printf("%d\n", i);

   pf = *sqr;
   i = pf(5);
   printf("%d\n", i);

   return 0;
}