结点的插入

#include <stdio.h>
#include <malloc.h>
#define LEN sizeof(struct student)

struct student
{
     long num;
     int score;
     struct student *next;
};

struct student *create(int n)
{
     struct student *head=NULL,*p1=NULL,*p2=NULL;
     int i;
     for(i=1;i<=n;i++)
     {  p1=(struct student *)malloc(LEN);
        scanf("%ld",&p1->num);
        scanf("%d",&p1->score);
        p1->next=NULL;
        if(i==1) head=p1;
        else p2->next=p1;
        p2=p1;
      }
      return(head);
}
void print(struct student *head)
{
    struct student *p;
    p=head;
    while(p!=NULL)
    {
        printf("%8ld%8d",p->num,p->score);
        p=p->next;
        printf("\n");
    }
}

struct student *insert(struct student *head, struct student *stud)
{
   struct student *p0,*p1,*p2;
   p1=head;//头指针
   p0=stud;//第二个指针
   if(head==NULL)
   {
       head=p0;
       p0->next=NULL;
   }
   else
    {
        while((p0->num>p1->num)&&(p1->next!=NULL))//比较学号的大小
   {
       p2=p1;
       p1=p1->next;
   }
   if(p0->num<p1->num)
   {
       if(head==p1)
       {
           head=p0;
       }
       else
        p2->next=p0;
       p0->next=p1;
   }
   else
   {
       p1->next=p0;
   }
   }
   return head;
}
int main()
{
    struct student *head,*stu;
    int n;
    scanf("%d",&n);
    head=create(n);
    print(head);
    stu=(struct student *)malloc(LEN);
    scanf("%ld",&stu->num);
    scanf("%d",&stu->score);
    stu->next = NULL;
    head=insert(head,stu);
    print(head);
    return 0;
}
/*struct student *insert(struct student *head, struct student *stud)
{  struct student *p0,*p1,*p2;
    p1=head;  p0=stud;
    if(head==NULL)//空表，直接插入,head等于p0
      {head=p0;}
    else//循环找到适合的位置
   { while( (p0->num > p1->num) && (p1->next!=NULL) )
       { p2=p1;     p1=p1->next;}//记住p1之前的结点
     if( p0->num < p1->num )//表头或是中间的位置
      {  if( head==p1 ) head=p0;//要插入的位置刚好是表头
           else p2->next=p0;//插入中间位置
         p0->next=p1; }
     else {  p1->next=p0;}//插入表尾
     }
    return(head);
}*/