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;
}