string wangZhi;         //网址
            string leiXing;         //网址的类型

            Console.WriteLine("输入网址：");
            wangZhi = Console.ReadLine();
            //索引最后一个点
            int suoYin = wangZhi.LastIndexOf(".");
            leiXing = wangZhi.LastIndexOf(0.suoYin);          //获得网址的类型
                                          ---------
            if (suoYin>0)
            {
                switch (leiXing)
                {
                    case "com":
                        Console.WriteLine("商业");
                        break;
                    case "net":
                        Console.WriteLine("网络服务");
                        break;
                    case "org":
                        Console.WriteLine("非盈利机构");
                        break;
                    default:
                        Console.WriteLine("输入错误!");
                }
            }

suoYin那有问题！
系统提示是：int 不包含 suoYin 的定义.

哎

找出问题了：
leiXing = wangZhi.LastIndexOf(0.suoYin);         

在字符串处理方法种
括号中的0和suoYin
要用  ，（逗号）隔开不是  .  （句号）

要是不注意的话
就会显示错误是：

int 不包含 suoYin 的定义.