程序代码：

void Insert()
{
    struct Student *p1,*p2;
    int point;
    int i=1;
    system("cls");
    p1=head;
    if (n==0)
    {
        printf("这是一张空表,返回菜单\n");
        return;
    }
    printf("请输入插入节点的位置,现在共有%d个节点(输入0或小于-1退出,输入-1输出链表)\n",n);
    if (scanf("%d",&point)&&point<=0&&point!=-1)
        return;
    fflush(stdin);
    if (point==-1)
    {
        print();
        return Insert();
    }
    if (point>n)
    {
        printf("找不到该节点,请重新输入\n\n");
        fflush(stdin);
        Insert();
    }
    printf("请输入学生的学号和成绩(学号输入0或负数退出)\n");
    printf("%d--",n+1);
    p2=malloc(LEN);
    if (scanf("%d%d",&p2->num,&p2->score)&&p2->num<=0)
        return;
    n++;
    while (1)
    {
        if (point==1)
        {
            p2->next=head;
            head->back=p2;
            head=p2;
            head->back=NULL;
            return Insert();
        }
        if (point==n-1)
        {
            end->next=p2;
            p2->back=end;
            end=p2;
            end->next=NULL;
            return Insert();
        }
        if (point!=i++)
            p1=p1->next;
        else
        {
            p2->next=p1;
            p2->back=p1->back;
            p1->back->next=p2;
            p1->back=p2;
            return Insert();
        }
    }
}
void Delete()
{
    struct Student *p=head;
    int point,i=1;
    system("cls");
    if (n==0)
    {
        printf("这是一张空表,返回菜单\n");
        return;
    }
    printf("请输入需要删除的节点编号(现在共有%d个节点,输入0或小于-1退出,输入-1输出链表)\n",n);
    if (scanf("%d",&point)&&point<=0&&point!=-1)
        return;
    fflush(stdin);
    if (point==-1)
    {
        print();
        return Delete();
    }
    if (point>n)
    {
        printf("找不到该节点，请重新输入\n\n");
        fflush(stdin);
        return Delete();
    }
    while (1)
    {
        if (point==1&&n!=1)
        {
            head=head->next;
            free(head->back);
            head->back=NULL;
            n--;
            return Delete();
        }
        if (point==n&&n!=1)
        {
            end=end->back;
            free(end->next);
            end->next=NULL;
            n--;
            return Delete();
        }
        if (n==1)
        {
            free(head);
            head=NULL;
            n--;
            printf("这是一张空表,返回菜单\n");
            return;
        }
        if (point!=i++)
            p=p->next;
        else
        {
            p->back->next=p->next;
            p->next->back=p->back;
            free(p);
            n--;
            return Delete();
        }
    }
}