C#实现数字转换

using System;

namespace Csharp6_2
{
    class Program
    {
        static void Main(string[] args)
        {
            while(true)
            {
                while (true)
                {
                    Console.Write("Please input a string : ");
                    string numStr;
                    double num;
                    numStr = Console.ReadLine();
                    if (double.TryParse(numStr, out _))
                    {
                        num = System.Convert.ToDouble(numStr);
                        Console.WriteLine("Successfully , the number is : " + string.FORMat("{0:N4}", num));
                        break;
                    }
                    else
                    {
                        Console.WriteLine("Failing , Please input a string again ! ");
                    }
                }
                Console.ReadLine();
            }
        }
    }
}