Calculate the Factorial of an Integer in C#

It could be done using Recursive Lambda Expression, for example,

class Program
{
    static Func<int, int> Factorial = x => x < 0 ? -1 : x == 1 || x == 0 ? 1 : x * Factorial(x - 1);

    static void Main(string[] args)
    {
        Console.WriteLine(Factorial(5));
    }
}

(The code is based on the References sites.) From the above code, Factorial is variable of type Func<int,int> which is holding a anonymous method. So following line of code...

 x => x < 0 ? -1 : x == 1 || x == 0 ? 1 : x * Factorial(x - 1)

...is the anonymous method and is equivalent to:

int Factorial( int x ){
  if( x<0){
     return -1;
  }else if( x==1 || x==0 )
  {
     return 1;
  }else{
     return x* Factorial(x-1);
  }
}

It is also possible to generate a Factorial for a number without recursion, for example, the following code block will calculate without the recursive method call:

private static int Factorial(int i)
{
    int result = i < 0 ? -1 : i == 0 || i == 1 ? 1 : 1;
    if (i > 0)
        Enumerable.Range(1, i).ToList<int>().ForEach(element => result = result * element);
    return result;
}

and also using Aggregate function of Linq:

private static int Factorial(int i)
{
    return i < 0 ? -1 : i == 0 || i == 1 ? 1 : Enumerable.Range(1, i).Aggregate((counter, value) => counter * value);
}

(initial idea to use Aggregate function found in here[^].) References [1] http://msdn.microsoft.com/en-us/library/0yw3tz5k(VS.80).aspx[^] [2] http://en.wikipedia.org/wiki/Recursion[^] [3] Factorial Simplified using lambda[^] [4] http://stackoverflow.com/questions/1426715/factorial-of-n-numbers-using-c-lambda[^] [5] http://blogs.msdn.com/b/madst/archive/2007/05/11/recursive-lambda-expressions.aspx[^] :)