using System;

using System.Collections.Generic;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        // var IpRegEx = @"\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b";   // 355.168.0.1 = 355.168.0.1 (Not Correct   All IPs in the list report as valid)

        // var IpRegEx = @"((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)";  // 355.168.0.1 = 55.168.0.1 (Not correct)

        // var IpRegEx = @"\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}";  // 355.168.0.1 = 355.168.0.1 (Not Correct  - All IPs in the list report as valid)

        // var IpRegEx = @"^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$";  // 355.168.0.1 = 355.168.0.1 (Not Correct  - All IPs in the list report as valid)

        // var IpRegEx = @"^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$";  // 355.168.0.1 = 355.168.0.1 (Not Correct - All IPs in the list report as valid)

        // Newly added expressions after my post on Stackedoverflow.

        // var IpRegEx = @"\A\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3}\z";  // Incorrect added by Adit Kothari.

        // var IpRegEx = @"^(\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.(\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.(\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.(\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])$"; // This works correctly.  Added by Denis

        // var IpRegEx = @"(\d{1,3}\.){3}(\d{1,3})[^\d\.]";  // Incorrect added by asdfgasdfas.

        // Working regular expression.

        var IpRegEx = @"^(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9])\.(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]|0)\.(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]|0)\.(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[0-9])$";  // 355.168.0.1 = No Match (Correct)

        var ipList = new List<string>();

        ipList.Add("355.168.0.1"); // Invalid

        ipList.Add("192.168.0.1"); // Valid

        ipList.Add("192.300.300.300"); // Invalid

        ipList.Add("10.28.38.8"); // Valid

        ipList.Add("255.255.255.0"); // Valid

        ipList.Add("255.256.0.0");  // Invalid

        ipList.Add("355.168.0.1");  // Invalid

        ipList.Add("0.254.255.0"); // Invalid

        foreach (var curIp in ipList)

        {

            var match = Regex.Match(curIp, IpRegEx);

            if (match.Success)

            {

                Console.WriteLine("{0}\tMatches (Considered Valid)", match.Value);

            }

            else

            {

                Console.WriteLine("{0}\tDoes not match. (Considered Invalid)", curIp);

            }

        }

    }

}