How to use std::list

sample.cpp

#include <iostream>
#include <list>
#include <algorithm>
#include <iterator>

int main()
{
    std::list<int> ls { 12, 2, 3, 1, 5, 4, 13, 7, 8, 9, 10, 11, 6};
    // とりあえず出力
    std::copy(ls.begin(), ls.end(), std::ostream_iterator<int>(std::cout, " "));
    std::cout << "\n"; 

    // 4を探す
    auto iter = std::find(ls.begin(), ls.end(), 4);
    int index = static_cast<int>(std::distance(ls.begin(), iter));
    
    // ４がでるまで引きます
    for (int i = 0; i < index; i++)
    {
        ls.pop_front();
    }

    std::copy(ls.begin(), ls.end(), std::ostream_iterator<int>(std::cout, " "));
    std::cout << "\n"; 
    
    return 0;
}