allow textbox to support numbers and OemMinus only?

allow textbox to support numbers and OemMinus only?

in my code i use this peace of code to validate textbox to support only
numbers
private void card_No_KeyDown(object sender, KeyEventArgs e)
{
nonNumberEntered = false;
// Determine whether the keystroke is a number from the top of the
keyboard.
if (e.KeyCode < Keys.D0 || e.KeyCode > Keys.D9)
{
// Determine whether the keystroke is a number from the keypad.
if (e.KeyCode < Keys.NumPad0 || e.KeyCode > Keys.NumPad9 &&
e.KeyCode == Keys.Oemplus)
{
// Determine whether the keystroke is a backspace.
if (e.KeyCode != Keys.Back)
{
// A non-numerical keystroke was pressed.
// Set the flag to true and evaluate in KeyPress event.
nonNumberEntered = true;
}
}
}
}
private void card_No_KeyPress(object sender, KeyPressEventArgs e)
{
if (nonNumberEntered == true)
{
MessageBox.Show("not allowed");
e.Handled = true;
}
}`, but know i want my textbox to allow OemMinus (-) character ? how
can i do this?