! counting a, b, c ,...
PROGRAM ex7_5

  IMPLICIT NONE
  INTEGER :: freq(0:27) = 0, code(255) = 0, i, ichi
  CHARACTER :: abc*53, input*80
  LOGICAL :: mask(0:27)

  abc = " ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"

  ! make a code table
  ! 空白とアルファベット以外は code = 0 とする
  DO ichi = 1, 53
    IF ( ichi <= 27 ) THEN
      code( ICHAR( abc(ichi:ichi) ) ) = ichi
    ELSE
      code( ICHAR( abc(ichi:ichi) ) ) = ichi - 26    ! 小文字の処理
    END IF
  END DO

  ! sentence input and count frequency of each characters
  DO
    PRINT '(1X, A)', "Write a sentence shorter than 80 characters: "
    READ '(A)', input
    IF ( input == "" ) EXIT
    DO i = 1, LEN_TRIM(input)
      ichi = code( ICHAR( input(i:i) ) )
      freq(ichi) = freq(ichi) + 1
    END DO
  END DO

  ! array sorting with use of mask
  freq(0) = 0; mask = ( freq > 0 )         ! 論理配列式とその代入
  DO WHILE( COUNT(mask) > 0 )              ! freq > 0 での最大値を調べる
    ichi = SUM( MAXLOC( freq, mask ) ) - 1 ! MAXLOC は要素数１の配列(注)
    PRINT '(5X, A1, " : ", I5)', abc(ichi:ichi), freq(ichi)
    mask(ichi) = .FALSE.
  END DO

  PRINT '(1X, "total = ", I5)', SUM( freq )

END PROGRAM ex7_5