program main

  open(11, file='file.dat', status='replace')
  write(11, *) 'aaa'

  call write_string()

  close(11)

!--------------------------------------------------------------
!
!--------------------------------------------------------------
contains
subroutine write_string()
  implicit none

  write(11, *) 'bbb'
end subroutine write_string
!--------------------------------------------------------------
!
!--------------------------------------------------------------
end program main