! generating a hexadecimal expression
FUNCTION hex( n )

  IMPLICIT NONE
  INTEGER, INTENT(IN) :: n
  INTEGER :: j, nn, nin
  CHARACTER(LEN=8) :: hex
  CHARACTER(LEN=1) :: h(0:15) = (/ '0', '1', '2', '3', '4', '5', &
                                   '6', '7', '8', '9', 'a', 'b', &
                                   'c', 'd', 'e', 'f' /)
  nin = n
  hex = ' '
  DO j = 8, 1, -1
    nn = nin / 16
    hex(j:j) = h(nin-16*nn)    ! (j:j)は引数ではなく文字部分列の記号
    IF ( nn == 0 ) EXIT
    nin = nn
  END DO

END FUNCTION hex
! main
PROGRAM ex8_3

  IMPLICIT NONE
  INTEGER :: i
  CHARACTER(LEN=8) :: hex

  PRINT '(1X, A)', 'Input a positive integer or negative one to stop: '

  DO
    READ *, i
    IF ( i < 0 ) EXIT
    PRINT '(1X, A8)', hex(i)
  END DO

END PROGRAM ex8_3