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));
        }

    }
}