Lecture - 24.cpp

//
//  main.cpp
//  Lecture - 24
//
//  Created by Prince  Kumar on 28/03/19.
//  Copyright © 2019 Prince  Kumar. All rights reserved.
//  seive of eratosthenes -- //

#include <iostream>
#include <cstring>
using namespace std;

void seive( int n)
{
    // create boolean array
    bool prime[n+1];
    memset(prime, true ,sizeof(prime));
    
    for(int p=2;p*p<=n;p++)
    {
        //  if prime[p] --> false  --> it is not prime
        if(prime[p]==true)
        {
            for(int i=p*p;i<=n;i=i+p)
            {
                prime[i]=false;
            }
        }
    }
    
    // print prime numbers
    for(int j=2;j<=n;j++)
    {
        if(prime[j]==true)
            cout<<j<<endl;
    }
}
int main()
{
    cout <<"Enter number upto which you want to print prime numbers "<<endl;
    int n ; cin>>n;
    seive(n);
}