c++ count vector elements
// 1.
for(std::vector<int>::iterator it = vector.begin(); it != vector.end(); ++it)
sum_of_elems += *it;
// 2.
// #include <numeric>
sum_of_elems = std::accumulate(vector.begin(), vector.end(), 0);
// C++11 and higher
// 3.
// #include <numeric>
sum_of_elems = std::accumulate(vector.begin(), vector.end(),
decltype(vector)::value_type(0));
// 4.
for (auto& n : vector)
sum_of_elems += n;