双向链表（创建、求长、打印、删除、插入）

#include<iostream>using namespace std;typedef struct student{int data;student *pre;student *next;}dnode;dnode* creat(){dnode *head, *p, *s;head = new dnode;p = head;int cycle = 1;int x;while (cycle){cout<<"Please input data : "<<endl;cin>>x;if (x){s = new dnode;s->data = x;p->next = s;s->pre = p;p = s;}else cycle = 0;}head = head->next;head->pre = NULL;p->next = NULL;cout<<"The data of head is : "<<head->data<<endl;return head;}int length(dnode* head){dnode *p;p = head;int length_count = 0;while (p){p = p->next;++length_count;}cout<<"The length of dlink is : "<<length_count<<endl;return length_count;}dnode* print(dnode* head){dnode *p;p = head;cout<<"The print result is: "<<endl;while (p){cout<<p->data<<" ";p = p->next;}cout<<endl;return head;}dnode* delete_node(dnode* head, int num){dnode *p, *q;p = head;int flag = 0;if (NULL == p)return head;else{while (num == p->data){q = p;p = p->next;head = p;head->pre = NULL;delete q;}p = p->next;while (p){if (num == p->data){if (!flag)flag = 1;if (p->next){q = p;p = p->next;p->pre = q->pre;q->pre->next = p;delete q;}else{q = p;p = NULL;q->pre->next = NULL;delete q;}}elsep = p->next;}if (!flag)cout<<"There is no data you want to delete!"<<endl;return head;}}dnode* insert_node(dnode* head, int num){dnode* p, *s;p = head;s = new dnode;s->data = num;while (s->data > p->data && NULL != p->next){p = p->next;}if (s->data <= p->data){if (head == p){s->next = p;p->pre = s;head = s;}else{p->pre->next = s;s->next = p;s->pre = p->pre;p->pre = s;}}else{p->next = s;s->pre = p;s->next = NULL;}return head;}int main(){dnode* link_original =  creat();length(link_original);print(link_original);cout<<"Please input the num you want to delete: "<<endl;int num;cin>>num;dnode* link_after_delete = delete_node(link_original, num);print(link_after_delete);cout<<"Please input the node you want to insert: "<<endl;int input_num;cin>>input_num;dnode* result_after_insert =  insert_node(link_after_delete, input_num);print(result_after_insert);}