! mean and standard deviation
PROGRAM ex5_4

  IMPLICIT NONE
  INTEGER :: n = 0, mark
  REAL :: w = 0.0E0, v = 0.0E0, mean, sd

  DO
    PRINT '(1X, A)', '点数（整数：終了は負の数）は？'
    READ *, mark

    IF ( mark < 0 ) EXIT        ! これでループを抜ける。
    n = n + 1
    w = w + mark
    v = v + mark ** 2
  END DO

  IF ( n > 0 ) THEN
    mean = w / n
    sd = SQRT( v / n - mean ** 2 )
    PRINT '(1X, "平均点   = ", F5.1)', mean
    PRINT '(1X, "標準偏差 = ", F5.1)', sd
  END IF

  PRINT '(1X, "生徒総数 = ", I5)', n

END PROGRAM ex5_4