San nguyen to (Prime Sieve algorithm)

void SieveOfEratosthenes(int n)

{

    // Create a boolean array "prime[0..n]" and initialize

    // all entries it as true. A value in prime[i] will

    // finally be false if i is Not a prime, else true.

    bool prime[n+1];

    memset(prime, true, sizeof(prime));

  

    for (int p=2; p*p<=n; p++)

    {

        // If prime[p] is not changed, then it is a prime

        if (prime[p] == true)

        {

            // Update all multiples of p greater than or 

            // equal to the square of it

            // numbers which are multiple of p and are

            // less than p^2 are already been marked. 

            for (int i=p*p; i<=n; i += p)

                prime[i] = false;

        }

    }

  

    // Print all prime numbers

    for (int p=2; p<=n; p++)

       if (prime[p])

          cout << p << " ";

}