void Stack::operator=(const Stack &original)
{
Stack new_copy(original);
Node * temp=top_node;
top_node=now_copy.top_node;
now_copy.top_node=temp;
}
void Stack::operator=(const Stack &original)
{
Stack new_copy(original);
Node * temp=top_node;
top_node=now_copy.top_node;
now_copy.top_node=temp;
}