#include <iostream>
#include <vector>
#include <algorithm>

int main()
{
    std::vector<int> v = {6,3,4,5,6,7,8,6,9};
    
    int pos = -1;
    std::vector<int>::iterator it = v.begin();
    
    while((it = std::find(it, v.end(), 6)) != v.end())
    {
        pos = it - v.begin();
        std::cout << "6 is at pos " << pos << std::endl;
        ++it;
    }
}