Definitions

   The factorial of   0   (zero)   is defined as being   1   (unity).
   The   Factorial Function   of a positive integer,    n,    is defined as the product of the sequence:
                 n,   n-1,   n-2,   ...   1 



Task

Write a function to return the factorial of a number.

Solutions can be iterative or recursive.

Support for trapping negative    n    errors is optional.



Related task

   Primorial numbers


import "/fmt" for Fmt
import "/big" for BigInt
 
class Factorial {
    static iterative(n) {
        if (n < 2) return BigInt.one
        var fact = BigInt.one
        for (i in 2..n.toSmall) fact = fact * i
        return fact
    }
 
    static recursive(n) {
        if (n < 2) return BigInt.one
        return n * recursive(n-1)
    }
}
 
var n = BigInt.new(24)
Fmt.print("Factorial(%(n)) iterative -> $,s", Factorial.iterative(n))
Fmt.print("Factorial(%(n)) recursive -> $,s", Factorial.recursive(n))