program testoptargs
implicit none
interface
  subroutine testopt(one,two,three,four,five)
    integer, intent(in) :: one,two
    integer, intent(out) :: three
    real, intent(in), optional :: four
    real, intent(out), optional :: five
  end subroutine testopt
end interface
integer :: iout
real :: rout

write(6,"(/)")
call testopt(1,2,iout)                        ! call w/o optional args
write(6,"('After main call testopt(1,2,iout): iout=',i4)") iout

write(6,"(/)")
call testopt(1,2,iout,5.,rout)
write(6,"('After main call testopt(1,2,iout,5.,rout): iout=',i4,' rout=',f10.2)") &
  iout,rout

end program testoptargs
!-----------------------------------------------------------------------
subroutine testopt(one,two,three,four,five)
implicit none
integer, intent(in) :: one,two
integer, intent(out) :: three
real, intent(in), optional :: four
real, intent(out), optional :: five

three = one + two
write(6,"('testopt: one=',i4,' two=',i4,' three=',i4,' present(four)=',l1,' present(five)=',l1)") &
  one,two,three,present(four),present(five)

end subroutine testopt