C#

using System;
using System.Runtime.InteropServices;
 
class DetectDevice
{
  static void Main()
  {
    int id = CeGetDeviceId();
    if (id == 0)
      Console.WriteLine("Device not connected.");
    else if (id == -1)
      Console.WriteLine("Quest device connected.");
    else
      Console.WriteLine("Device ID: " + id);
  }
 
  [DllImport("ceutil.dll")]
  static extern int CeGetDeviceId();
}

private double factorial(double f)
{
    double num = Math.Floor(f);
    if(num < 0)
    {
        return -1;
    }
    if(num == 0)
    {
        return 1;
    }
    else
    {
        return (num * factorial(num - 1));
    }
}

public static BigInteger factorial( int n )
{
   BigInteger result = new BigInteger(1);
   for( int i = 1; i <= n; i++ )
      result = result * i;
   return result;
}
... And later, in Main(): 
Console.WriteLine("factorial of 170  = " + factorial(170) );