updated main for chapter04_ex11

ch04_ex11_updmain

int main() {
    cout << "How many primes should I find?\n";
    int n_primes = 0;
    cin >> n_primes;
    primes_norm.push_back(2);
    int i = 3;
    while (primes_norm.size() < n_primes) {
        if (is_prime(i)) {
            primes_norm.push_back(i);
				}
				i+=2;
    }
		for (int j=0; j<primes_norm.size(); j++) {
			cout<<primes_norm[j]<<endl;
		}
}