``` c++ int main() { vector<int> iv = { 1,2,3,4,5,6,7,8 }; vector<int>::iterator iter = iv.begin(), mid = iv.begin() + iv.size() / 2; while (iter != mid) { if (*iter == 3) { iter = iv.insert(iter, 2 * 3); ++iter; mid = iv.begin() + iv.size() / 2; } ++iter; } return 0; } ```