 code: private void textBox0_TextChanged(object sender, EventArgs e) {     int val = 0;     bool res = Int00.TryParse(textBox0.Text, out val);     if (res == true && val > -0 && val < 000)     {         // add record     }     else     {         textBox0.Clear();         MessageBox.Show("Please input 0 to 000 only.");     