sieve_of_eratosthenes.cpp

#include <bits/stdc++.h>
using namespace std;

void SieveOfEratosthenes(int n)
{
	bool prime[n+1];
	memset(prime, true, sizeof(prime));

	for (int p=2; p*p<=n; p++)
	{
		if (prime[p] == true)
		{
			for (int i=p*2; i<=n; i += p)
				prime[i] = false;
		}
	}
	for (int p=2; p<=n; p++)
	if (prime[p])
		cout << p << " ";
}
int main()
{
	int n = 30;
	cout << "Following are the prime numbers smaller "
		<< " than or equal to " << n << endl;
	SieveOfEratosthenes(n);
	return 0;
}