Else's blog

            if (!Char.IsNumber(e.KeyChar) && !Char.IsPunctuation(e.KeyChar) && !Char.IsControl(e.KeyChar))
            {
                e.Handled = true;
            }
            else if (Char.IsPunctuation(e.KeyChar))
            {
                if (e.KeyChar == '.')
                {
                    if (((TextBox)sender).Text.LastIndexOf('.') != -1)
                    {
                        e.Handled = true;
                    }
                }
                else
                {
                    e.Handled = true;
                }
            }