template<class type>
void List<type>::addElement( type data )
{
    if( this->head == NULL ) {

        element_struct* tmp_struct = new element_struct();
        tmp_struct->data = data;
        tmp_struct->next = NULL;

        tail = head = tmp_struct;
    }
    else {
        element_struct* tmp_struct = new element_struct();
        tmp_struct->data = data;
        tmp_struct->next = NULL;

        tail->next = tmp_struct;
        tail=tmp_struct;
    }

    cout << "Элемент добавлен!" << endl;
}