countif http://www.cplusplus.com/reference/algorithm/count_if/

// count_if example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

bool IsOdd (int i) { return ((i%2)==1); }

int main () {
int mycount;

vector<int> myvector;
for (int i=1; i<10; i++) myvector.push_back(i); // myvector: 1 2 3 4 5 6 7 8 9

mycount = (int) count_if (myvector.begin(), myvector.end(), IsOdd);
cout << "myvector contains " << mycount  << " odd values.\n";

return 0;
}