void add_element(const int& element)
{
    //int* newBuffer = new int;
    //*newBuffer = element;
    //memcpy(buffer, newBuffer, sizeof (newBuffer));
    int* newBuffer = new int[capacity + 1];
    memcpy(newBuffer, buffer, sizeof(buffer)*capacity);
    newBuffer[capacity] = element;
    delete[] buffer;
    buffer = newBuffer;
    capacity = capacity + 1;
}

const int& get_element(const unsigned& index) {
    if (index < 0 || index > capacity) {
        throw std::runtime_error("index is invalid");
    }
    else {
        return buffer[index];
    }
}