C++ 链表的一个问题，找不出来

Question

while (p && q)

{
    if (p->element <= q->element)
    {
        if (newNode)
        {
            newNode->next = p;
            newNode->next->previous = newNode;
            newNode = newNode->next;
            p = p->next;
        }
        else
        {
            newNode = firstNode = p;
            firstNode->previous = nullptr;
            p = p->next;
        }
    }

    if (p && p->element > q->element) 
    {
        if (newNode)
        {
            newNode->next = q;
            newNode->next->previous = newNode;
            newNode = newNode->next;
            q = q->next;
        }
        else
        {
            newNode = firstNode = q;
            firstNode->previous = nullptr;
            q = q->next;
        }
    }
}

当我给下一个节点赋值时，全部值都为0了

Answer 1

缺乏必要的描述，程序的主要功能是什么？newNode, p, q的初始值是什么？