! 例題 8-3  16進数変換をする外部関数 ［外部関数 ］
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 )    ! 左辺は文字部分列の記号
    IF ( nn == 0 ) EXIT
    nin = nn
  END DO

END FUNCTION hex

! main
PROGRAM ex8_3

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

  PRINT *, '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