How can I say "Code not found"?

If you've uncommented the red line, then I can't see what else can possibly be null here so you you'll need to try and indentify the offending line with the debugger.

Just one point though. Is the 'code' column a numeric or char based column in the database?

If it's numeric, then you won't need the surrounding single quotes in the SELECT query.

 

First of all, if you uncomment the red line, does the code build OK?

If it does, are you getting a null reference exception when you try to run it and are you able to pinpoint, using the debugger, on which line the exception occurs?

please let see what I do. I have this message: Object reference not set to an instance of an object

Notice that I've placed the declarations for the variables sqlCon and read at the top of the method. They shouldn't be declared again within the try statement or you'll get the compiler error you're now getting - they should simply be assigned to.

If you're sure that "Code" is the only column which might not be found, you could do this:

private void btnSearch_Click(object sender, EventArgs e)
{
   SqlConnection sqlCon = null;
   SqlDataReader read= null;
 
   try
   {
      string connectionString = @"Data Source=localhost\sqlexpress;Initial Catalog=master;Integrated Security=True";
      sqlCon = new SqlConnection(connectionString);
      sqlCon.Open();
      string commandString = "select code, product, stocks from  searching where code='" + code.Text + "'";
      SqlCommand sqlCmd = new SqlCommand(commandString, sqlCon);
      read = sqlCmd.ExecuteReader();

      while (read.Read())
      {
         code.Text = read["code"].ToString();
         product.Text = read["product"].ToString();
         Stocks.Text = read["stocks"].ToString();
      }
   }
   catch(IndexOutOfRangeException)
   {
      MessageBox.Show("Code not found. Thanx!");
   }
   catch(Exception ex)
   {
      MessageBox.Show(ex.Message);
   } 
   finally
   {
      read.Close();    
      sqlCon.Close();
   }
}