program t03
  implicit none
  real::x
  integer::i,n
  character(16)::form = '(x,i2,"! = ",i9)'
  call rms(2.0,4.0,x)
  print'(a,f5.2)',"The rms is",x
  do i = -20,20
   if (is_perfect_square(i)) print*,i,"is a perfect square"
  end do
  do i = 0,12
   print form,i,factorial(i)
  end do


 contains

  subroutine rms(x,y,z)
   implicit none
   real, intent(in)::x,y
   real, intent(out)::z
   z = sqrt((x**2+y**2)/2)
  end subroutine rms

  logical function is_perfect_square(n)
   implicit none
   integer,intent(in)::n
   is_perfect_square = n >= 0 .and. nint(sqrt(real(abs(n))))**2 == n
  end function is_perfect_square

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
! The type of a function can be declared in the header line.  This !
! alternative method is shown as a comment line below.             !
! If this alternative is used, delete the header line and also the !
! line that specificies integer type for the result identifier.    !
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

! recursive integer function factorial(n) result(fact)
  recursive function factorial(n) result(fact)
   implicit none
   integer,intent(in)::n
   integer::fact
   if (n < 0) then
    print 10, "Error in function factorial: negative argument not allowed"
10  format(a)
   else if (n == 0) then
    fact = 1
   else
    fact = n * factorial(n-1)
   end if
  end function factorial
 
 end program t03