using System;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            test te = new test();
            Console.WriteLine(te.codeNumber("AB00230001", 5000));
        }
        class test
        {
          public string codeNumber(string source, int num)
            {
             string str1 = Regex.Match(source, @"[0-9]+", RegexOptions.RightToLeft).Value;
             string begin = str1.Substring(0, source.Length - str1.Length);
             return begin + (int.Parse(str1) + num-1).ToString().PadLeft(str1.Length, char.Parse("0"));
            }   
        }
    }
}
上面几行代码.
当            Console.WriteLine(te.codeNumber("AB00230001", 5000));
时,结果是0000235000,但我想要的是AB00235000,请问函数要改那里?

using System;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;
 
 
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            test te = new test();
            Console.WriteLine(te.codeNumber("AB00230001", 5000));
            Console.ReadLine();
        }
        class test
        {
            public string codeNumber(string source, int num)
            {
                string str1 = Regex.Match(source, @"[0-9]+", RegexOptions.RightToLeft).Value;
                //string begin = str1.Substring(0, source.Length - str1.Length);
                string begin = source.Substring(0, source.Length - str1.Length);
                return begin + (int.Parse(str1) + num - 1).ToString().PadLeft(str1.Length, char.Parse("0"));
            }
        }
    }
}