Use NumberFormatInfo to format a number : NumberFormatInfo : Development Class C# Source Code

    



using System;
using System.Globalization;
public class MainClass {
    public static void Main() {

        NumberFormatInfo f = new NumberFormatInfo();
        f.CurrencySymbol = "$$";
        Console.WriteLine(3.ToString("C", f));          // $$ 3.00

    }
}