C++ Pointer to Functions

#include <iostream>

long sum(long a, long  b);                           // Function prototype

long product(long a, long  b);                       // Function prototype

int main() {/*  ww w. ja  v  a2  s .  c  o  m*/
  long(*pDo_it)(long, long) {};                       // Pointer to function

  pDo_it = product;
  std::cout << "3*5 = " << pDo_it(3, 5) << std::endl; // Call product thru a pointer

  pDo_it = sum;                                       // Reassign pointer to sum()
  std::cout << "3 * (4+5) + 6 = " << pDo_it(product(3, pDo_it(4, 5)), 6) << std::endl;  // Call thru a pointer twice
}

// Function to multiply two values
long product(long a, long b)
{
  return a*b;
}

// Function to add two values
long sum(long a, long b)
{
  return a + b;
}