Finding Prime Numbers by Sieve Eratosthenes Method

// C++ program to print all primes smaller than or equal to 

// n using Sieve of Eratosthenes 

#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] 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 << " "; 

} 

 

int main() 

{ 

int n = 30; 

SieveOfEratosthenes(n); 

return 0; 

}