C++ Stirling Approximation

Simple C++ program to calculate Stirling approximation (factorial approximation).

#define _USE_MATH_DEFINES

#include <iostream>
#include <math.h>

// 2018 TheFlyingKeyboard and released under MIT License
// theflyingkeyboard.net
int main() {
  const double c = 2.506628274631000502415765284811045253006986740609938316629;
  int n = 1;
  double stirling = 1;

  std::cout << "Enter n" << std::endl;
  std::cin >> n;

  stirling = c * sqrt(n) * pow(n / M_E, n);

  std::cout << "Striling approximation of " << n << "! is equal to " << stirling << ", rounded " << round(stirling) << std::endl;

  int a;
  std::cin >> a;

  return 0;
}