双链表的建立、查找、删除、插入

#include <iostream>#include <stdio.h>#include <string.h>#include <conio.h>using namespace std;typedef struct student{  int data;  struct student *next;  struct student *pre;}dnode;//双链表的建立dnode * creat(){  dnode *head,*p,*s;  int x,cycle =1;  head = (dnode*)malloc(sizeof(dnode));  p=head;  while(cycle) {    printf("\n 请输入数据:");    scanf("%d",&x);    if (x !=0)    {      s= (dnode*) malloc(sizeof(dnode));      s->data = x;      printf("\n %d",s->data);      p->next = s;      s->pre =p;      p= s;    }    else cycle = 0;} head = head->next;//此时的head指向双链表中第一个有数据元素的节点 head->pre= NULL; p->next =NULL; printf("\n  第一个有数据元素的节点的数据:%d",head->data); return (head);}//双链表的查找dnode *find(dnode *head, int num){   dnode *p;   p1 = head;   while(p != NULL && p1->data !=num)   {     p=p->next;   }  if (p=NULL)  {    printf("未找到该数据");  }    return p;}//双链表的删除dnode *del(dnode *head, int num){    dnode *p1,*p2;    p1 = head;    while(num != p1->data && p1->next !=NULL)    {      p1=p1->next;    }    if (num == p1->data)    {        if(p1==head)//要删除的节点为表头节点      {         head=head->next;         head->pre =NULL;      }      else if(p1->next == NULL)//要删除的节点为表尾节点      {         p1->pre->next = NULL;      }      else//要删除的节点处于表中间      {         p1->next->pre = p1->pre;         p1->pre->next = p1->next;       }    free(p1);   }    else printf("\n %d 未找到该数据",num);   return (head);}//双链表的插入dnode *insert(dnode *head,int num){     dnode *p0,*p1; p1=head;     p0=(dnode*)malloc(sizeof(dnode));     p0->data = num;     while(p0->data >p1->data && p1->next != NULL)     {       p1=p1->next;      }     //三种位置的插入，表头，表尾，表中间     if (p0->data <= p1->data)     {        if (head == p1) //在表头插入节点         {            p0->next =p1;            p1->pre = p0;            head =p0;         }        else //在表中间插入节点        {            p1->pre->next=p0;            p0->next =p1;            p0->pre=p1->pre;            p1->pre =p0;        }    }    else //在表尾插入节点   {       p1->next =p0;       p0->pre=p1;       p0->next=NULL;     }}int main() {        dnode *head,stud;        int n,del_num,insert_num;        head = creat();        print(head);        cout < "\n nInt: ";        cin >> del_num;        head = del(head,del_num);        print(head);        cout << "\n 请输入要插入的数据:";        cin >> insert_num;        head = insert(head,insert_num);        print(head);        return 0;}