(1) . 输入注册时的用户名和密码，登录成功，提示欢迎信息
(2) . 如果用户名和密码输入错误，提示用户继续输入，最多有3次输入机会

 static void Main(string[] args)
    {
        int max = 99999;
        int min = 1000;
        Random rd = new Random();
        rd.Next(min, max);
        int a = 0;
        string user = "";
        string key = "";
        string b = "";
        Console.WriteLine("*****欢迎进入奖客富翁系统*****");
        Console.WriteLine("           1.注册");
        Console.WriteLine("           2.登录");
        Console.WriteLine("           3.抽奖");
        Console.WriteLine("******************************");
        Console.WriteLine("请选择菜单：");
        a = Convert.ToInt32(Console.ReadLine());
        switch (a)
        {
            case 1:
                Console.WriteLine("[奖客富翁系统>注册]");
                Console.WriteLine("请填写用户注册信息:");
                Console.WriteLine("用户名:");
                user = Console.ReadLine();
                Console.WriteLine("密码:");
                key = Console.ReadLine();
                Console.WriteLine("注册成功，请记好你的会员卡号");
                Console.WriteLine("用户名\t\t密码\t\t会员卡号");
                Console.WriteLine("{0}\t\t{1}\t\t{2}", user, key, rd.Next(min, max));
                Console.WriteLine("继续吗?(y/n)");
                b = Console.ReadLine();
                break;
            case 2:
                Console.WriteLine("[奖客富翁系统>登录]");
                user = "admin";
                key ="123456";
                int i=2;
                while (i > -1)
                {
                    Console.WriteLine("请输入用户名:");
                    string yonghu = Console.ReadLine();
                    Console.WriteLine("请输入密码:");
                    string mima = Console.ReadLine();
                    if (user == yonghu & key == mima & i > 0)
                    {
                        Console.WriteLine("欢迎您:{0}", yonghu);
                        break;
                    }
                    else
                    {
                        if (i > -1)
                        {
                            Console.WriteLine("你还剩{0}次机会", i);
                            i--;
                            continue;
                        }
                        else
                        {
                            Console.WriteLine("你的机会用完了");
                            break;
                        }
                    }
                }
                break;
            case 3:
                Console.WriteLine("[奖客富翁系统>抽奖]");
                break;
        }
        Console.WriteLine("继续吗？（y/n）");
        b = Console.ReadLine(); switch (b)
        {
            case "n":
                Console.WriteLine("系统退出，谢谢使用");
                break;
            case "y":
                Console.WriteLine("");
                break;
        }
        Console.ReadKey();
    }