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// A sample program demonstrating using Google C++ testing framework.

//

// Author: wan@google.com (Zhanyong Wan)

#include "sample1.h"

// Returns n! (the factorial of n).  For negative n, n! is defined to be 1.

int Factorial(int n) {

  int result = 1;

  for (int i = 1; i <= n; i++) {

    result *= i;

  }

  return result;

}

// Returns true iff n is a prime number.

bool IsPrime(int n) {

  // Trivial case 1: small numbers

  if (n <= 1) return false;

  // Trivial case 2: even numbers

  if (n % 2 == 0) return n == 2;

  // Now, we have that n is odd and n >= 3.

  // Try to divide n by every odd number i, starting from 3

  for (int i = 3; ; i += 2) {

    // We only have to try i up to the squre root of n

    if (i > n/i) break;

    // Now, we have i <= n/i < n.

    // If n is divisible by i, n is not prime.

    if (n % i == 0) return false;

  }

  // n has no integer factor in the range (1, n), and thus is prime.

  return true;

}