程序代码：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<conio.h>
#define LEN sizeof(struct zhanghu)
struct zhanghu
{
    char zhanghu_zhanghao[20];
    char zhanghu_mima[16];
    struct zhanghu *next;
};
int n;
int zhuce(struct zhanghu *head,struct zhanghu *p1,struct zhanghu *p2)
{
    int len,ch;
        while(p1->zhanghu_zhanghao!=0)
    {
        n=n+1;
        if(n==1)head=p1;
        else p2->next=p1;
        p2=p1;
        p1=(struct zhanghu *)malloc(LEN);
    printf("帐号：");
lable1:
    gets(p1->zhanghu_zhanghao);
    len=strlen(p1->zhanghu_zhanghao);
    if(len>20)
    {
        printf("过长\n");
        printf("请重新输入帐号：");
        goto lable1;
    }
    if(len<6)
    {
        printf("过短\n");
        printf("请重新输入帐号：");
        goto lable1;
    }
    printf("\n密码：");   
lable2:
    while((p1->zhanghu_mima=getch())!='\n')
    printf("*");
    len=strlen(p1->zhanghu_mima);
    if(len>16)
    {
        printf("过长\n");
        printf("请重新输入密码：");
        goto lable1;
    }
        if(len<6)
    {
        printf("过短\n");
        printf("请重新输入密码：");
        goto lable1;
    }
        }
}
/*void denglu(struct zhanghu head,struct zhanghu *p1,struct zhanghu *p2)
{
    char zhanghaoa[],mimaa[];
    printf("帐号：");
    gets(zhanghaoa);
    printf("\n密码:");
    gets(mimaa);
}*/
struct zhanghu *creat(void)
{
    struct zhanghu *p1,*p2;
    struct zhanghu *head;
    char a;
    head=NULL;
    n=0;
    p1=p2=(struct zhanghu *)malloc(LEN);
    zhuce(head,p1,p2);
    /*printf("是否注册帐号Y，或N，或登录L:");
    scanf("%c",&a);
    if(a='Y'||'y')
        zhuce(head,p1,p2);
    if(a='N'||'n')
        denglu(head,p1,p2);*/
}
/*还没写完,为什么会报错？我觉得已经对了吧！
*/