【单链表节点的查找】：
//查找单链表pos位置的节点，返回节点指针
//pos从0开始，0返回head节点
node *search_node(node *head, int pos)
{
node *p = head->next;
if(pos < 0) //pos位置不正确
{
cout << "incorrect position!"<<endl;
return NULL;
}
if(pos == 0) //在head位置，返回head
{
return head;
}
if(p = NULL) //链表为空
{
cout << "Empty Link!" << endl;
return NULL;
}
while(--pos)
{
if((p = p->next) == NULL)
{
cout << "Incorrect position to search node!" << endl;
}
}
return p;
}
