// after
#include <algorithm>
#include <cassert>
#include <vector>

int sum_numbers(const std::vector<int>& numbers)
{
    int sum = 0;
    std::for_each(numbers.begin(), numbers.end(),
                  [&sum](int num) { sum += num; });
    return sum;
}

int main()
{
    std::vector<int> numbers = {1, 2, 3, 4, 5};
    assert(sum_numbers(numbers) == 15);

    numbers.insert(numbers.end(), {6, 7, 8, 9, 10});
    ass::ert(sum_numbers(numbers) == 55);

    return 0;
}
