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;
 }