! hexadecimal notation
PROGRAM ex7_1

  IMPLICIT NONE
  INTEGER :: dec, i
  CHARACTER(LEN=1)::h(0:15) = (/ '0','1','2','3','4','5','6','7', &
                                 '8','9','a','b','c','d','e','f' /)
  CHARACTER(LEN=8) :: hex

  ext: DO
    hex = ' '
    PRINT '(1X, A)', 'Input a positive integer, or 0 to stop: '
    READ *, dec
    IF ( dec <= 0 ) EXIT ext
    hxd: DO i = 0, 7
      hex(8-i:8-i) = h(MOD( dec, 16 ))
      dec = dec / 16
      IF ( dec == 0 ) EXIT hxd
    END DO hxd
    PRINT '(1X, A8)', hex
  END DO ext

END PROGRAM ex7_1