#include <stdio.h>


// Take in a pointer-to-a-function, two arguments for the function,
// and apply the function. Return the result.

double applyFunction (double (*func)(double, double),  double x, double y)
{
  double z;                 // For result.

  z = (*func) (x, y);       // Apply the function. Note the parentheses around "*func".
  return z;
}


// How to declare a function prototype when an argument is a pointer-to-function:
char * funcName ( double (*func)(double, double) );


//---------------------------------------------------------------------
// Test code.

// A test function. Take in a pointer-to-a-function, apply it,
// print it's name and result of applying the function.

void test ( double (*func)(double, double) )
{
  double x, y, z;
  char *name;

  x = 1.0;  y = 2.0;                  // Test values.
  z = applyFunction (func, x, y);     // Send the function itself to "applyFunction".
  name = funcName (func);             // Likewise to "funcName".
  printf ("x = %lf  y = %lf  %s(x,y) = %lf\n", x, y, name, z);
}


// Some function prototypes that will be used in testing.

double max (double, double);
double min (double, double);
double absDiff (double, double);

int main () 
{
  test (max);
  test (min);
  test (absDiff);
}


//---------------------------------------------------------------------
// The function implementations:

double max (double x, double y)
{
  if (x > y)
    return x;
  else
    return y;
}

double min (double x, double y)
{
  if (x < y)
    return x;
  else
    return y;
}


double absDiff (double x, double y)
{
  if (x > y)
    return (x - y);
  else
    return (y - x);
}


// Take in a pointer-to-a-function and print its name.

char * funcName ( double (*func)(double, double) )
{
  if (func == max) {
    return "maximum";
  }
  else if (func == min) {
    return "minimum";
  }
  else if (func == absDiff) {
    return "absoluteDifference";
  }
}