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program main
implicit none
	call menu()
end program main

recursive subroutine menu() !'recursive' is needed if the subroutine or function will call itself either directly or implicit
	integer :: choice
	logical :: valid !A boolean to indicate if the input is valid (.TRUE. or .FALSE.)
	print *, '--------------------'
	print *, '-----Calculator-----'
	print *, '--------------------'
	print *, 'Addition 1'
	print *, 'Subtraction 2'
	print *, 'Multiplication 3'
	print *, 'Division 4'
	print *, 'High precision division 5'
	print *, 'Power 6'
	print *, 'Terminate 0'
	valid = .FALSE.	!Make shure the while loop runs atleast once
	do while (.NOT.valid)
		read *, choice
		valid = .TRUE.
		if (choice == 1) then
			call addition()
		else if (choice == 4) then
			call division()
		else if (choice == 5) then
			call hp_division()
		else if (choice == 6) then
			call power()
		else if (choice == 0) then
			print *, 'Program finished'
		else
			print *, 'False input, please enter valid input: '
			valid = .FALSE.
		end if
	end do
end subroutine menu