string aa="SELECT MAX(CONVERT(int, SUBSTRING(tab_mc, 5, 3))) FROM t_xt_table";
  cc=sql.ExecuteScalar(aa).ToString().Trim();
  if(cc=="")
  {
  temp1="user" +1;
  }
  else

  {
  bb=Convert.ToInt32(cc) + 1;
  temp1="user" + bb;  }