Factorial
You are encouraged to solve this task according to the task description, using any language you may know.
The Factorial Function is the product of a sequence n, n-1, n-2...1 starting at the input number to the function.
Write a function to factorialise a number. Solutions can be iterative or recursive (though recursive solutions are generally considered too slow and are mostly used as an exercise in recursion). Support for negative n errors is optional.
References
Ada
<Ada> function Factorial (N : Positive) return Positive is
Result : Positive := N; Counter : Natural := N - 1;
begin
for I in reverse 1..Counter loop
Result := Result * I;
end loop;
return Result;
end Factorial; </Ada>
Python
Iterative
<python>def factorial(n):
z=n
while n>1:
n=n-1
z=z*n
return z
</python>
Recursive
<python>def factorial(n):
z=1
if n>1:
z=n*factorial(n-1)
return z
</python>
ALGOL 68
Iterative
PROC factorial = (INT in n)LONG LONG INT:(
INT n := in n;
LONG LONG INT z := n;
WHILE n>1 DO
n -:= 1;
z *:= n
OD;
z
); ~
Recursive
PROC factorial = (INT n)LONG LONG INT:(
IF n>1 THEN
n*factorial(n-1)
ELSE
1
FI
); ~