factorial en c#

this is an algorithm that is able to return a factorial number,
algoritmo para generar un factorial de un numero


using System;
namespace  factorial
{
public class program
{
static void Main()
{
double num;
            Console.WriteLine("digite numero");
num = double.Parse(Console.ReadLine());
            Console.WriteLine("el factorial\n"+ program.factorial(num));
            Console.Read();
}

static double factorial(double num)

{
double  f=1;
for(int i =1;i <= num; i++)
f =f*i;
return f;
}

static double factorialrec(double numero)
{
if (numero ==1)
return 1;
else
return numero*factorialrec(numero-1);
}

}
}