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


const max_size = 10
 
fn factorial_i() {
  mut facs := [0].repeat(max_size + 1)
  facs[0] = 1
  println('The 0-th Factorial number is: 1')
  for i := 1; i <= max_size; i++ {
    facs[i] = i * facs[i - 1]
    num := facs[i]
    println('The $i-th Factorial number is: $num')
  }
}
 
fn main() {
	factorial_i()
}