TheAlgorithms-C-Plus-Plus/others/primality_test.cpp

#include <iostream>
using namespace std;

//A simple and efficient implementation of a function to test if a number is prime, based on the fact that
//Every Prime number, except 2 and 3 are of the form 6*k+1 or 6*k-1 for integer values of k.

bool IsPrime(int number)
{
	if (((!(number & 1)) && number != 2) || (number < 2) || (number % 3 == 0 && number != 3))
		return false;

	for (int k = 1; 36 * k * k - 12 * k < number; ++k)
	{
		if ((number % (6 * k + 1) == 0) || (number % (6 * k - 1) == 0))
			return false;
	}
	return true;
}

int main()
{
	//Main Function
	cout << "Enter the value of n to check if Prime\n";
	int n;
	cin >> n;
	if (IsPrime(n))
		cout << n << " is Prime" << endl;
	else
		cout << n << " is not Prime" << endl;

	return 0;
}