建立的是一个有序的管理学生信息的双向链表，功能有创建，插入，删除， 遍历， 查找等。

#include <iostream>
#include <string>
using namespace std;
typedef long long LL;

struct List{
	int num;
	string name;
	LL tel;
	struct List * prior;
	struct List * next;
};
List *Insert(List *head, List *tmp);	// 插入函数声明
List *create()
{
	List *head, *p;		// 头结点和待插入节点
	int num;
	string name;
	LL tel;
	head = NULL;	// 头结点初始为空
	cout << "input num, name and tel: \n";
	cin >> num >> name >> tel;
	while(num)		// 输入编号为0退出
	{
		p = new List;
		p->num = num;
		p->name = name;
		p->tel = tel;
		head = Insert(head, p);		// 调用插入函数插入新节点
		cin >> num >> name >> tel;
	}
	return head;	// 返回创建的链表的头结点的地址
}
List *Insert(List *head, List *tmp)
{
	List *ptr, *ptr1, *ptr2;	// 定义辅助指针
	ptr2 = head;	// 初始 ptr2 指向头结点
	ptr = tmp;		// 初始 ptr 是指向待插入节点
	if(head == NULL)	// 如果头结点还为空
	{
		head = ptr;		// 头结点为待插入结点
		head->prior = NULL;	// 前驱也为NULL
		head->next = NULL;	// 因为此时还没有下一个节点，所以head->next 为空
	}
	else	// 如果头结点不为空
	{	// 寻找带插入结点应该插入的位置，链表的顺序是num从小到达的顺序
		while((ptr->num > ptr2->num) && (ptr2->next != NULL))
		{
			ptr1 = ptr2;	// ptr1 是 ptr2 的前驱结点
			ptr2 = ptr2->next;	// ptr2 后移
		}
		if(ptr->num <= ptr2->num)
		{
			if(head == ptr2)	// ptr2是头结点
			{
				head = ptr;		// 插入到头结点前面，头结点前移
				head->prior = NULL;	// 头结点前没有结点了
				head->next = ptr2;	// 新的头结点的后继
				ptr2->prior = head;	// 下一个结点的前驱
				ptr2->next =NULL;	// 后继没有结点了
			}
			else	// 插入在两个结点的中间
			{
				ptr1->next = ptr;
				ptr->prior = ptr1;
			}
			ptr->next = ptr2;
			ptr2->prior = ptr;
		}
		else	// 插入在末尾
		{
			ptr2->next = ptr;
			ptr->prior = ptr2;
			ptr->next = NULL;
		}
	}
	return head;
}
List *Delete(List *head, int num)
{
	List *ptr1, *ptr2;	// 辅助指针
	while(head != NULL && head->num == num)
	{
		ptr2 = head;
		head = head->next;	// 头结点后移
		head->prior = NULL;
		delete ptr2;	// 删除之前的头结点
	}
	if(head == NULL)	// 如果没有节点
		return NULL;
	ptr1 = head;
	ptr2 = head->next;
	while(ptr2 != NULL)
	{
		if(ptr2->num == num)
		{
			ptr1->next = ptr2->next;
			if(ptr2->next != NULL)		// 如果是最后一个结点则不能执行这一步
				ptr2->next->prior = ptr1;
//			ptr2->next->prior = ptr2->prior;
			delete ptr2;
		}
		else
			ptr1 = ptr2;
		ptr2 = ptr1->next;
	}
	return head;
}
void Print(List *head)	// 遍历输出函数
{
	List *ptr;
	if(head == NULL)
	{
		cout << endl << "No Records" << endl;
		return;
	}
	cout << "num\t name\t tel\n";
	ptr = head;
	while(ptr != NULL)
	{
		cout << ptr->num << "\t ";
		cout << ptr->name << "\t ";
		cout << ptr->tel << endl;
		ptr = ptr->next;
	}
}
List *Find(List *head, int num)
{
	List *flag = NULL;
	for(List *ptr = head; ptr != NULL; ptr = ptr->next)
	{
		if(ptr->num == num)
		{
			flag = ptr;
		}
	}
	return flag;
}

int main()
{
	List *head, *p;
	int num;
	string name;
	LL tel;
	int choice;

	do{
		cout << "1: create\n2: insert\n3: delete\n4: print\n5: Find\n0: exit\n";
		cin >> choice;
		switch(choice)
		{
			case 1:
				head = create();
				break;
			case 2:
				cout << "input num, name and tel: \n";
				cin >> num >> name >> tel;
				p = new List;
				p->num = num;
				p->name = name;
				p->tel = tel;
				head = Insert(head, p);
				break;
			case 3:
				cout << "input num" << endl;
				cin >> num;
				head = Delete(head, num);
				break;
			case 4:
				Print(head);
				break;
			case 5:
				cin >> num;
				List * ptr = Find(head, num);
				if(ptr != NULL)
				{
					if(ptr->prior != NULL)	// 如果有前驱结点，输出前驱的人的名字
						cout << ptr->prior->name << endl;
					cout << ptr->name << "\t ";
					cout << ptr->tel << endl;
				}
				else
					cout << "No Find" << endl;
		}
	}while(choice != 0);


	return 0;
}