A TextBox Which Accept Only String in C#

public form()

{
    initializeComponent();
    textbox.text.keypress + = new keypressEventHandler(text.box_keypress);
}

 Now drag and down a textbox and click on "Keypress event" 

private void textbox_keypress(obj sender, event e)

{
    char pressedkey = e.keychar;
    if(char.IsLetter(pressedkey)||char.IsSeparator(PressedKey)||char.IsPunction(pressedKey))
    {
        e.handled = false;
    }
    else
    e.handled = true;
}