Numeric TextBox

Question

Im new to programming and I dont know very much about but I\'m making a calculator, and i want to use a textbox that only acepts numbers and decimals, and when the user past

Answer 1

        if ("1234567890".IndexOf(e.KeyChar.ToString()) > 0)
        {
            e.Handled = false;
        }
        else
        {
            e.Handled = true;
        }