Detect decimal separator

Solution:

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    char a = Convert.ToChar(Thread.CurrentThread.CurrentCulture.NumberFormat.NumberDecimalSeparator);
    if (e.KeyChar == a)
    {
        e.Handled = true;
        textBox1.Text = "0";
    }
}

That way, when you hit . or , you will have a 0 in your TextBox.

EDIT:

If you want to insert a 0 everytime you hit the decimal separator, this is the code:

char a = Convert.ToChar(CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator);
if (e.KeyChar == a)
{
    e.KeyChar = '0';
}

Actually you should be using

CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator

instead of

CultureInfo.CurrentUICulture.NumberFormat.NumberDecimalSeparator

Using the second one gives you the OS default settings, which might be different then user Regional Locales for particular user account logged to this PC.

Credits to berhir and Grimm for pointing out the [docs]

You shouldn't use a while loop, I think it will freeze the application, use if instead, the problem might be here