C++ 双向链表的简单操作

#include <iostream>

using namespace std;
typedef struct student{
int data;
struct student *next;
struct student *pre;
}dnode;

dnode *Create()
{
dnode *head,*p1,*p2;
int x,cycle = 1;
head = new dnode;
p1 = head;
while (cycle)
{
cin>>x;
if (x != -1)
{
p2 = new dnode;
p2->data = x;
p1->next = p2;
p2->pre = p1;
p1 = p2;
}
else
cycle = 0;
}
head = head->next;
head->pre = NULL;
p1->next = NULL;
return head;

}

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)
{
head = head->next;
head->pre = NULL;
delete p1;
}
else if(p1->next == NULL)
{
p1->pre->next = NULL;
delete p1;
}
else
{
p1->next->pre = p1->pre;
p1->pre->next = p1->next;
}
}
else
{
cout<<"can not find the num!\n";
}
return  head;
}

dnode *insert(dnode *head,int num)
{
dnode *p0,*p1;
p1 = head;
p0 = new dnode;
p0->data = num;
while (p0->data>p1->data&&p1->next!= NULL)
{
p1 = p1->next;
}
if (p0->data<=p1->data)
{
if (head == p1)
{
p0->next = p1;
p1->pre = p0;
head = p0;
}
else
{
p1->pre->next = p0;
p0->next = p1;
p0->pre = p1->pre;
p1->pre = p0;
}
}
else    //插入链表尾
{
p1->next = p0;
p0->pre = p1;
p0->next = NULL;
}
return head;
}

void print(dnode *head)
{
dnode *p1;

p1 = head;
if (p1 == NULL)
{
cout<<"the dnode is empty!\n";

}
else
{
while(p1!= NULL)
{
cout<<p1->data<<"  ";
p1 = p1->next;
}
}

}

int main()
{
dnode *head,stud;
head = Create();
print(head);
return 0;
}