Solution 2
recursive subroutine factorial(n, factorial_n) ! Dummy arguments integer, intent(in) :: n real, intent(out) :: factorial_n ! Determine whether further recursion is required select case(n) case(0) ! Recursion has reached the end factorial_n = 1.0 case(1:) ! Recursive call(s) required ! to obtain (n-1)! call factorial(n-1, factorial_n) case default ! n is negative - return zero as an error indicator factorial_n = 0.0 end subroutine factorial