#include <stdio.h>

#define NULL 0

struct unit
{
    int num;
    struct unit *next;
    struct unit *forward;
};

struct unit *head;

struct unit *create(void)
{
    struct unit *p1, *p2;
    int i;
    p2 = p1 = (struct unit*)malloc(sizeof(struct unit));
    head = p1;
    for (i = 0; i < 10; i++)
    {
        p1 -> num = i;
        p2 = p1;
        p1 = (struct unit*)malloc(sizeof(struct unit));
        p2 -> next = p1;
        p1 -> forward = p2;
    }
    p2 -> next = head;
    head -> forward = p2;
}

void print()
{
    struct unit *p;
    int i = 0;
    p = head;
    printf("............\n");
    for (i = 0; i < 10; i++)
    {
        printf("%d\n",p->num);
        p = p -> next;
    }
    printf("\n");
    p = head -> forward;
    for (i = 0; i < 10; i++)
    {
        printf("%d\n",p->num);
        p = p -> forward;
    }
    printf("............\n");
}

int search(int input)
{
    struct unit *p;
    if (head->num == input)
        return 0;
    else
    {
        p = head -> next;
        do
        {
            if (p->num == input)
                return 0;
            else
                p = p ->next;
        }while(p != head);
    }
    return 1;
}

void delete()
{
    struct unit *p;
    int del;
    p = head;
    printf("Input the number you want to delete!\n");
    scanf("%d\n",&del);
    if (head->num == del)
        head = p -> next;
    if (search(del) == 1)
        printf("The number you want to delete doesn't exist!\n");
    else
    {
        while (p->next->num != del)
            p = p -> next;
        p -> next -> next -> forward = p;
        p -> next = p -> next -> next;
    }
    print();
}

int searchcore()
{
    int input;
    printf("Please input the number you want to search!\n");
    scanf("%d\n",&input);
    return search(input);
}

void insert()
{
    int ins,pos;
    int i;
    struct unit *p, *new;
    printf("Please input the number you want to insert!\n");
    scanf("%d\n",&ins);
    printf("Please input the position you want to put the number!\n");
    scanf("%d\n",&pos);
    p = head;
    for (i = 0; i < pos; i++)
        p = p -> next;
    new =  (struct unit*)malloc(sizeof(struct unit));
    new -> num = ins;
    p -> next -> forward = new;
    new -> next = p -> next;
    p -> next = new;
    new -> forward = p;
    print();
}

main()
{
    create();
    /*print();
    printf("\n");
    if (searchcore() == 0)
        printf("Found!\n");
    else
        printf("Not Found!\n");
    delete(); */
    insert();
    getch();
}

小弟多年不写，前些天想写个Linear找找感觉
但是void insert()时遇到比较奇怪的事情
就是两次Scanf前一次被要求输入两次，好像第一次没有用，（这样就总共输入两次），但计算机采取的数据却只是3次中的两次，我以前从来没遇到过这种情况啊。。。
大家可以试试在自己这里运行，到底是我写的有问题，还是TC有问题呢？

这是数据结构方面的基础问题，我能帮你解答，去这个两博客其中的一个，把问题写到留言版上，我马上给你解答。
http://dlstudenting.
http://fxstudenting.blog.

去掉scanf中的\n