vector enumeration

std::vector<int> h;
size_t size = h.size();

for (int i : h) {
    std::cout << i << std::endl;
}

int i = 0;
std::vector<std::vector<double>> matrix(100, std::vector<double>(100));

for (std::vector<double> &line : matrix) {
    for (double &elem : line) {
        elem = i++;
    }
}

for (std::vector<std::vector<double>>::iterator iter = matrix.begin(); iter != matrix.end(); ++iter) {
    for (std::vector<double>::iterator innerIter = iter->begin(); innerIter != iter->end(); ++innerIter) {
        *innerIter = i++;
    }
}

for (auto iter = matrix.begin(); iter != matrix.end(); ++iter) {
    for (auto innerIter = iter->begin(); innerIter != iter->end(); ++innerIter)
        *innerIter = i++;
}

for (std::vector<double> &line : matrix) {
    for (double &elem : line) {
        std::cout << elem << " ";
    }
    std::cout << std::endl;
}