std::copy defined in the header
<algorithm>. The args are a pointer to the first element of the input, a pointer to one past the last element of the input, and a pointer to the first element of the output.
( https://en.cppreference.com/w/cpp/algorithm/copy )
int * result = new int[size1 + size2]; std::copy(arr1, arr1 + size1, result); std::copy(arr2, arr2 + size2, result + size1);
vector will do better as a dynamic array rather than pointer