using System;
using System.Net;

namespace ConsoleApp5
{
    class Program
    {
        static void Main(string[] args)
        {
            string str = "127.0.0.1";
            string ip = ConvertIPAddress(str);
            if (!string.IsNullOrEmpty(ConvertIPAddress(ip)))
            {
                Console.WriteLine("有效ip: {0}", ip);
            }
            else
            {
                Console.WriteLine("無效ip");
            }
            Console.Read();
        }

        /// <summary>
        /// 將字符串轉換為IP
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        private static string ConvertIPAddress(string str)
        {
            IPAddress tmpIp;
            if (IPAddress.TryParse(str, out tmpIp))
            {
                return IPAddress.Parse(str).ToString();
            }
            else
            {
                return "";
            }
        }

    }
}