#include <stdio.h>
#include <string.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;
}


// A typedef for a function-pointer:
typedef double (*funcPointerType)(double, double);

// getFunction is declared as a function that returns a funcPointerType, 
// and is declared to itself take a char* parameter.
funcPointerType getFunction(char *str);

int main () 
{
  double x, y, z;
  double (*func)(double, double);

  x = 1.0;  y = 2.0;                  // Test values.
  func = getFunction ("max");         // Get back a function-pointer. 
  z = applyFunction (func, x, y);     // Send the function-pointer to another function.
  printf ("x = %lf  y = %lf  max(x,y) = %lf\n", x, y, z);
}


//---------------------------------------------------------------------
// 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);
}


// Function that returns a function-pointer

funcPointerType getFunction (char *str)
{
  if (strcmp (str, "max") == 0) {
    return max;
  }
  else if (strcmp (str, "min") == 0) {
    return min;
  }
  else if (strcmp (str, "absDiff") == 0) {
    return absDiff;
  }
}