! 例題 5-4  平均値と標準偏差 ［途中で抜ける（EXIT）］
PROGRAM ex5_4

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

  DO n = 1, 1000
    PRINT *, '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

    w = w + mark
    v = v + mark ** 2
  END DO

  n = n - 1
  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