Count Primes Solutions in C++

// Source : https://leetcode.com/problems/count-primes/
// Author : Hao Chen
// Date   : 2015-06-09



#include <stdlib.h>
#include <iostream>
#include <vector>
using namespace std;

int countPrimes(int n) {
    vector<bool> isPrimer(n, true);

    for(int i=2; i*i<n; i++){
        if (isPrimer[i]){
            for(int j=i*i; j<n; j+=i){
                isPrimer[j] = false;
            }
        }
    }

    int cnt = 0;
    for(int i=2; i<n; i++){
        if (isPrimer[i]) { 
            //cout << i << ", ";
            cnt++;
        }
    }
    return cnt;
}


int main(int argc, char**argv) 
{
    int n = 100;
    if (argc>1){
        n = atoi(argv[1]);
    }
  
    cout << endl << n << " : " << countPrimes(n) << endl;

    return 0;
}