Fortran 95 source code to compute the factorial.

factorial.f95

!****************************************************
! 階乗計算
!
! date          name            version
! 2018.08.20    mk-mode.com     1.00 新規作成
!
! Copyright(C) 2018 mk-mode.com All Rights Reserved.
!****************************************************
!
program fact_main
  implicit none
  integer n

  do n = 0, 20
    write (*,'(I3,3X,I20)') n, fact(n)
  enddo

  stop
contains
  ! 階乗計算
  !
  ! :param  integer n
  ! :return integer fact
  integer(kind=8) recursive function fact(n)
    implicit none
    integer, intent(IN) :: n
    integer :: i

    fact = 1
    do i = 1, n
      fact = fact * i
    enddo
    return
  end function fact
end program fact_main