Sieve

#include <bits/stdc++.h>

using namespace std;
const int sz = 10000000;
bool isnt_prime[sz + 1];
void fix() {
    isnt_prime[0] = isnt_prime[1] = true;
    for (int i = 4; i <= sz; i += 2) isnt_prime[i] = true;
    for (int i = 3; i <= sqrt(sz); i++) {
        if (!isnt_prime[i]) {
            for (int j = 3; j * i <= sz; j += 2) isnt_prime[i * j] = true;
        }
    }

}
int main() {
    fix();
    for (int i = 0; i <= 100; i++) {
        if (!isnt_prime[i]) cout << i << " ";
    }
    return 0;
}