using System.Globalization;
public static void Main()
string decimalPoint = (amount).ToString();
decimalPoint = decimalPoint.Substring(decimalPoint.IndexOf(".") + 1);
if( decimalPoint.Length > 0)
Console.WriteLine(string.Format(new CultureInfo("en-US"),"{0:C" + decimalPoint.Length +"}", amount));
Console.WriteLine(string.Format(new CultureInfo("en-US"),"{0:C0}", amount));