代码如下,当表示层调用时就报错了,void无法隐式转换string.
using System;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;
namespace ConsoleApplication1
{
    class Program
    {
        public  void codeNumber(string source, string num)

        {
            int n1 = source.Length;
            int n2 = num.Length;
            string str1 = source.Substring(n1 - n2, n2);
            try
            { int str2 = Convert.ToInt32(str1);
              int num2 = Convert.ToInt32(num);
              int sum = str2 + num2-1;
              int n3 = sum.ToString().Length;
              if (n3 > n2)
              {
                  str1 = source.Substring(n1 - n2 - 1, n2 + 1);
                  str2 = Convert.ToInt32(str1);
                  sum = str2 + num2-1;
              }
              string str4 = source.Substring(0, n1 - n2) + sum.ToString();

              Console.WriteLine(str4);
          }

            catch
            {
                Console.WriteLine("输入有误");
            }

        }   
        static void Main(string[] args)
        {
            Program c = new Program();
            c.codeNumber("AB00230001", "70000");
         
        }
    }
}