So I'm trying to make a simple calculator. The user can only input the numbers by the buttons on the form or by the numpad. This is the code I have:

```
private void Form1_KeyDown(object sender, KeyEventArgs e)
    {
        string key = "";

        switch (e.KeyCode)
        {
            case (Keys.NumPad1):
                key = "1";
                break;
            case (Keys.NumPad2):
                key = "2";
                break;
            default:
                break;
        }

        txt_string.Text = txt_string.Text + key;
    }

```

If I make a breakpoint on the `KeyDown` function and press the Numpad keys (and every other keys) the program doesnt even comes to that breakpoint.

Do I have to change something on my Form to detect the Keys?