Sieve.cpp

//============================================================================
// Name        : Sieve.cpp
// Author      : Nick Coy
// Version     :
// Copyright   : 
// Description : Hello World in C++, Ansi-style
//============================================================================
#include <bits/stdc++.h>
#include <iostream>
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] is not changed,
        // then it is a prime
        if (prime[p] == true)
        {
            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 << " ";
}

// Driver Code
int main()
{
    int n;
    cout<<"Primes upto:";
    		cin>>n;
    cout << "Following are the prime numbers smaller "
         << " than or equal to " << n << endl;
    SieveOfEratosthenes(n);
    
    cin>>n;
    
    return 0;
}