private void Display_Click(object sender, EventArgs e)
{
  int i, sum, digit, num;
  listBox1.Items.Clear();
  for (i = 10000; i <= 99999; i++)
  {
     sum = 0;
     num = i;
     while (num > 0)
     {
        digit = num % 10;
        num = (int)num / 10;
        sum = (sum * 10) + digit;
      }
      if (sum == i) listBox1.Items.Add(i.ToString());
    }
}
