空位補零，你會選擇哪種方式？

隨便寫著玩的。。。

using System;

namespace KiloNet
{
    class  test
    {
        static void Main(string[] args)
        {
            //空位補零，你會選擇哪種方式？

            Console.WriteLine("pad('1',4)={0}",pad("1",4));
            Console.WriteLine("pad('12',4)={0}",pad("12",4));
            Console.WriteLine("pad('123',4)={0}",pad("123",4));
            Console.WriteLine("pad('1234',4)={0}",pad("1234",4));
            Console.WriteLine("pad('12345',4)={0}",pad("12345",4));
            Console.WriteLine("pad('123456',4)={0}",pad("123456",4));

            Console.WriteLine("pad2('1',4)={0}",pad2("1",4));
            Console.WriteLine("pad2('12',4)={0}",pad2("12",4));
            Console.WriteLine("pad2('123',4)={0}",pad2("123",4));
            Console.WriteLine("pad2('1234',4)={0}",pad2("1234",4));
            Console.WriteLine("pad2('12345',4)={0}",pad2("12345",4));
            Console.WriteLine("pad2('123456',4)={0}",pad2("123456",4));

            Console.WriteLine("pad3('1',4)={0}",pad3("1",4));
            Console.WriteLine("pad3('12',4)={0}",pad3("12",4));
            Console.WriteLine("pad3('123',4)={0}",pad3("123",4));
            Console.WriteLine("pad3('1234',4)={0}",pad3("1234",4));
            Console.WriteLine("pad3('12345',4)={0}",pad3("12345",4));
            Console.WriteLine("pad3('123456',4)={0}",pad3("123456",4));

            Console.Read();
        }

        //正常循環
        static string pad(string num, int n) {
            int i = num.Length;
            while(i++ < n) num = "0" + num;
            return num;
        }
        
        //遞歸
        static string pad2(string num, int n) {
            return (num.Length >= n)? num:pad2("0" + num, n);
        }

        //一次搞定
        static string pad3(string num, int n) {
            return ("".PadLeft(n, '0') + num).Substring(n+ num.Length - Math.Max(num.Length, n), Math.Max(num.Length, n));
        }

    }
}