int a = Convert.ToInt32(txt1.Text.Trim().Replace('[', ']').Split(']')[1]);
   string b = txt1.Text.Trim().Replace('[', ']').Split(']')[2]; 

string str = "[数字]字符串";
Regex reg = new Regex(@"
([^]+)\](.*)");
string a= Convert.ToInt32( reg.Match(str).Groups[1].Value);
string b= Convert.ToInt32( reg.Match(str).Groups[2].Value);

string tempStr = "[数字]字符串"; 
string pattern = @"
([\s§]∗)
([\s\S]*)";
Regex re = new Regex(pattern); 
string str1 = Regex.Replace(tempStr,pattern,"$1"); 
string str2 = Regex.Replace(tempStr, pattern, "$2");

  /// <summary>
  /// 返回一个字符串数组
  /// </summary>
  /// <param name="str"></param>
  /// <returns></returns>
  public string[] ReturnIDAndName(string str)
  {    
    string[] stringArray = new string[2];    
    Regex reg = new Regex(@"
([^]+)\](.*)");
    stringArray[0]= reg.Match(str).Groups[1].Value;
    stringArray[1] = reg.Match(str).Groups[2].Value;    
    return stringArray;
  } 
 
  /// <summary>
  /// 截取字符串编号
  /// </summary>
  public int ReturnId(string str)
  {
    try
    {
      if (string.IsNullOrEmpty(str))
      {
        return 0;
      }
      Regex regex = new Regex("(?<=\\[)\\d+(?=\\])");
      Match m = regex.Match(str);
      int pid;
      if (!m.Success)
      {
        pid = int.Parse("[" + regex.Match(str).Value + "]");
      }
      return int.Parse(regex.Match(str).Value);
    }
    catch
    {
      return 0;
    }
  }