ans0902.f90

program main
  implicit none
  character(len=79)  :: filename
  character(len=79)  :: buffer
  integer, parameter :: fileid = 10
  integer i
  integer :: status = 0
  logical alive

  write(*,*) "Filename:"
  read (*,"(A79)") filename
  inquire( file=filename, exist=alive)
  
  if ( alive ) then
    open(unit=fileid, file=filename, &
	     access="sequential", status="old")
    do while(.true.)
      read(unit=fileid, fmt="(A79)", iostat=status ) buffer
      if ( status/=0 ) exit  ! ûÓÐ×ÊÁϾÍÌø³öÑ­»·
	  do i=1, len_trim(buffer)
	    buffer(i:i) = char( ichar(buffer(i:i))-3 )
	  end do
      write(*,"(A70)") buffer
    end do
  else
    write(*,*) TRIM(filename)," doesn't exist."
  end if

  stop
end