using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var ser = new string[]{"5","5.00","-5","5.","-5.","-5.00"};

        foreach(var str in ser){

            string output = Test(str);

            Console.WriteLine(output);

        }

        //string input = "5, 5.00";

        //string output = Test(input);

        //Console.WriteLine(output);

    }

    //Sadece pozitif integer veya double sayılar

    //([+]?)\d+\.\d{0,2}$

    //([+]?)\s*(?:(?:(?:[^.([{0-9+-]?(\d+))|(\d+\.\d+(?!\w+)))(?!\w+|\.))(?![([{])

    private static readonly Regex Pattern = new Regex(@"([+]?)\s*(?:(?:(?:[^.([{0-9+-]?(\d+))|(\d+\.\d+(?!\w+)))(?!\w+|\.))(?![([{])", RegexOptions.Compiled);

​

    public static string Test(string input)

    {

        return Pattern.Replace(input, match =>

        {

            string newMatch = match.Groups[0].Value;

            return ">> " + newMatch + " <<";

        });

    }

}