/***********************
 *
 * Syntax for passing functions around
 *
 ***************/

#include <stdio.h>

// A simple function.
int doubleIt(int a) {
  return(2*a);
}

// And another with the same arguments and return value.
int halfIt(int a) {
  return (a/2);
}


int main() {

  int z = 17;
  int answer;

  int (*mysteryFunc)(int);	// here we declare mysteryFunc
				// as a pointer to a function which
				// takes an integer argument and returns
				// and integer.
  printf( " Hello \n " );
  printf( " twice %i is %i \n", z, doubleIt(z) );
  printf( " half %i is %i \n", z, halfIt(z) );

  mysteryFunc = &doubleIt;	// and here we assign whichFunc to
				// the address of the doubleIt function.

  mysteryFunc = doubleIt;	// This syntax also works.
  
				
  answer = mysteryFunc(z);	// And here we invoke it.
  answer = (*mysteryFunc)(z);	// Or this way.
  printf( " Mystery guest:  %i is %i \n", z, answer );

  // Here's how we compare two functions.
  if ( mysteryFunc == doubleIt ) {
    printf (" Yup, the mystery guest is 'doubleIt' \n");
  }
  else {
    printf (" Nope - something funny here.' \n");
  }

  // Or this.
  if ( mysteryFunc == &doubleIt ) {
    printf (" Yup, the mystery guest is 'doubleIt' \n");
  }
  else {
    printf (" Nope - something funny here.' \n");
  }


  // Or even this.  Go figure.
  if ( *mysteryFunc == doubleIt ) {
    printf (" Yup, the mystery guest is 'doubleIt' \n");
  }
  else {
    printf (" Nope - something funny here.' \n");
  }




}