! square root
PROGRAM ex5_7

  IMPLICIT NONE
  REAL :: r, x, d = 0.000005E0

  PRINT '(1X, A)', 'Input a real number: '
  READ *, r

  IF ( r > 0 ) THEN
    x = r                               ! 初期値は0以外なら何でもよい。
    DO WHILE( ABS( x ** 2 - r ) > d )
      x = 0.5E0 * ( x + r / x )
    END DO
    PRINT '(F8.5)', x
  END IF

END PROGRAM ex5_7