这个链表输入：“num  1,score 11”

              “num  2,score 22”

              “num  3,score 33”

              “num  4,score 44”

              “num  5,score 55”

              “num  6,score 66”

后若将“num 1”删除后，再次输出时第一个节点还是会被输出。删除别的都会正常输出。插入节点时，若插入的节点的num比最后一个大，那么这个节点会被插入到倒数第二个位置。。。这是为什么啊。我新手，弄不明白。。这个链表是自己做完后对着谭浩强老师的书改的。若哪位前辈愿意帮忙请指点一下。。谢谢。
#include<stdio.h>
#include<conio.h>
#include<malloc.h>
#define len sizeof(struct student)

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

struct student *creat()
{
  struct student *head,*p1,*p2;
  n=0;
  p1=p2=(struct student *)malloc(len);
  head=0;
  printf("shu ru xuehao:");
  scanf("%d",&p1->num);
  printf("shu ru score:");
  scanf("%d",&p1->score);
  while(p1->num!=0)
  {
    n=n+1;
    if(n==1)
    {
      head=p1;
    }
      else
      {
 p2->next=p1;
 p2=p1;
 p1=(struct student*)malloc(len);
 printf("shuru xuehao:");
 scanf("%d",&p1->num);
 printf("shuru score:");
 scanf("%d",&p1->score);
      }
  }
    p2->next=0;
    return (head);
}

void print(struct student *head)
{
  struct student *p;
  p=head;
  if(p==0)
  {
    printf("kongbuao");
  }
  else
  do
  {
    printf("num is:%d||score is:%d\n",p->num,p->score);
    p=p->next;
  }
  while(p!=0);
}

struct student *del(struct student *head,int num)
{
 struct student *p1,*p2;
 p1=head;
 if(head==0)
 {
  printf("\n list null \n");
  goto end;
 }
 p1=head;
 while(num!=p1->num&&p1->next!=0)
 {
  p2=p1;
  p1=p1->next;
 }
 if(num==p1->num)
 {
  if(p1==head)
  {
   head=p1->next;
  }
  else
  {
   p2->next=p1->next;
  }
  printf("delete :%d",num);
  n=n-1;
 }
 else
  printf("%d not been found!",num);
end:
 return head;
}

struct student *insert(struct student *head,struct student *stu)
{
 struct student *p1,*p2, *p3;
 p3=stu;
 p1=head;
 if(head==0)
 {
  head=p3;
  p3->next=0;
 }
 else
 {
  while(p3->num>p1->num&&p1->next!=0)
  {
   p2=p1;
   p1=p1->next;
  }
  p2->next=p3;
  p3->next=p1;
 }
 return head;
}

void main()
{
  struct student *head;
  int num;
  struct student *stu;
  clrscr();
  head=creat();
  print(head);
  printf("输入要删除的学号:");
  scanf("%d",&num);
  del(head,num);
  print(head);
  stu=(struct student*)malloc(len);
  printf("输入要插入的学号：");
  scanf("%d",&stu->num);
  printf("输入要插入的成绩：");
  scanf("%d",&stu->score);
  insert(head,stu);
  print(head);
  getch();
}