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


 
input string "Enter a number:"
set "in" to "('ABS('input')')"
if "in" <= 1 then "one"
set "result" to 1
 
: "factorial"
set "result" to "('result' * 'in')"
dec "in" by 1
if "in" > 1 then "factorial"
* "('result')"
end
 
: "one"
* "1"
end
 