Modules containing subroutines and functions in fortran - module

Question

I am learning correct use of subroutine, function and module, below is an simple example, no error occurs while compiling, after executing, the outcome is 4.57187637E-41 rather than pi, I have looked up several references, haven't found out the mistake yet.
module wz
implicit none
private
public :: print_out
real,parameter :: pi = 3.14159
contains
subroutine print_out
implicit none
real :: area
print *, area
end subroutine print_out
function f(x) result(area)
implicit none
real, intent(in):: x
real :: area
area = pi * x ** 2
end function f
end module wz
program test_module
use wz
implicit none
real :: x
x = 1.
call print_out
end program test_module

Answer 1

The value you are printing is area just after declaration and before doing anything with it. You need to pass x to f function, and you can do that via the print_out subroutine:
module wz
implicit none
private
public :: print_out
real,parameter :: pi = 3.14159
contains
subroutine print_out(x)
implicit none
real, intent(in) :: x
real :: area
area = f(x)
print *, area
end subroutine print_out
function f(x) result(area)
implicit none
real, intent(in):: x
real :: area
area = pi * x ** 2
end function f
end module wz
program test_module
use wz
implicit none
real :: x
x = 1.
call print_out(x)
end program test_module