This should be an easy problem but...
I need to format a currency for display (string) in C#
The currency in question will have its own rules such as the sym
To work with a textbox, try the following:
textBox2.Text = "Rp" + (textBox1.Text = string.Format(System.Globalization.CultureInfo.GetCultureInfo("id-ID"), "{0:#,##0.00}", double.Parse(textBox1.Text)));