把123456789转换为12-345-6789的3种方法

 
方法一：

 

            string a = "123456789";

            a = int.Parse(a).ToString("##-###-####");

            Console.Write(a);

 

方法二：

string a = "123456789";

            a = a.Insert(5, "-").Insert(2, "-");

            Console.Write(a);

方法三：

using System;

using System.Collections.Generic;

using System.Text;

using System.Text.RegularExpressions;

namespace ConsoleApplication1

...{

    class Program

    ...{

        static void Main()

        ...{

            string a = "123456789";

            Regex reg = new Regex(@"^(d{2})(d{3})(d{4})$");

            a = reg.Replace(a, "$1-$2-$3");

            Console.Write(a);

        }

       

    }

}