#include "stdio.h"
#include "stdlib.h"
#include "string.h"
struct student
{char name[80];
int a,b;
struct student *next;
}*creat();

struct student *creat()
{struct student *head=NULL,*tail=NULL,*p,*pp;
char name[80];
int a,b;
int size=sizeof(struct student);
scanf("%s%d%d",name,&a,&b);
while (a!=0){
p=(struct student *)malloc(size);
p->a=a;p->b=b;p->next=NULL;
strcpy(p->name,name);
if (head==NULL)
head=tail=p;
else
tail->next=p;
tail=p;
scanf("%s%d%d",name,&a,&b);}
for (pp=head;pp;pp=pp->next)
printf("%-7s%-5d%-5d\n",pp->name,pp->a,pp->b);
return (head);
}

void main()
{struct student *head;
head=creat();
｝

这是一个单向链表，请问怎么改就变成双向链表呢？