程序代码：

# include <stdio.h> //头文件
# include <string.h> //字符串头文件
# include <stdlib.h>

typedef struct in
{
    char id[20];//会员账号
    char key[20];//会员密码
    int sum;//会员积分
    struct in *next;
}member;

struct im//商品信息 以下是私有成员
{
    int id;//商品编号
    char name[50];//商品名称
    int stoct;//商品库存
}goods[1000];

member *registe(member *t);//注册；
void buy();

int main(void)
{
    member *head = (member *)malloc(sizeof(member));
    strcpy(head->id, "0"), strcpy(head->key, "0");//超市管理员
    head->next = NULL;
    int i, a, n, boo=0;
   
    while(1)
    {
        printf("注册会员请按1: \n");
        printf("会员直接登入请按2：\n");
        printf("推出请按0： \n");
        scanf("%d", &a);
        if (a == 0)
            break;
        if (a == 1)
            head = registe(head);
        else if (a == 2)
            boo = login(head);
        if (boo)
            break;       
    }
    if (a && boo==1)
    {
        printf ("尊贵的会员，您登入成功！\n");
        buy();
    }
    printf ("已经安全推出\n");
    return 0;
}
member *registe(member *t)//注册
{
    printf ("现在开始会员注册\n\n");
    char id[20], key[20];
    member *p, *q, *r;
    p = t;
    while(p->next) p = p->next;//寻找链表中最后一个节点
    while(1)
    {
        printf ("请输入您注册的账号, 密码：\n");
        scanf ("%s %s", id, key);
        q = t;
        while(q)//判断该账号是否已经被注册
        {
            if (strcmp (q->id, id)==0)
                break;
            else q = q->next;
        }
        if (q == NULL)//账号没有注册
        {
            r = (member *)malloc(sizeof(member));
            r->next = NULL;
            p->next = r;
            strcpy (r->id, id);
            strcpy (r->key, key);
            r->sum = 1000;//会员默认的积分为1000；
            break;
        }
        else
            printf ("该账号已被注册，请重新输入账号，密码\n");
    }
    printf ("恭喜您，已经注册成功，现在可以登入了\n\n");
   
    return t;
}

int login (member *t)//登入
{
    printf ("现在开始登入");
    member *p;
    char id[20],key[20];
    int a, boo = 0;
    while (1)
    {
        printf ("请输入您的账号，密码: \n");
        scanf ("%s", id);
        if (strcmp(id, "#")==0)
            break;
        scanf ("%s", key);
        p = t;
        while (p)
        {
            if (strcmp(p->id, id)==0 &&strcmp(p->key, key)==0)
                break;
            else
                p = p->next;
        }
        if (p == NULL)
        {
            printf ("对不起，该账号和密码错误，请重新登入\n");
            printf ("推出登入请按#\n");
        }
        else if
            (strcmp(id, "0")!=0)
        {
            boo = 1;
            break;
        }
    }
    return boo;   
}
void buy()
{
    char s[20];
    int n;
    int i;
    while(1)
    {
        printf ("请输入商品的编号或者名称:\n");
        scanf ("%s", s);
        if (strcmp(s, "0")==0)
            break;
        if (s[0]>='1' && s[0]<='9')
        {
            n = atoi(s);
            for (i=0; i<1000; i++)
            {
                if (goods[i].id == n)
                    break;
            }
            if (i > 1000)
            {
                printf ("商品不存在请重新输入，推出请按0\n");
            }
            else
            {
                printf ("您已购买成功。\n");
            }
        }   
        else
        {
            for (i=0; i<1000; i++)
            {
                if (strcmp(goods[i], s)==0)
                    break;
            }
            if (i > 1000)
            {
                printf ("商品不存在，请重新输入，推出请安0\n");
            }
            else
            {
                printf ("您购买成功.\n");
            }
        }
       
    }
}

在下 小白菜， 请帮我看下代码 哪里出错了~谢谢~~~~