a = a -= a * a首先计算 a * a = 3 * 3 = 9然后 a -= 9,相当于 a = a - 9,即 a = 3 - 9 = -6所以 a = -6a = a -= a *= a首先计算 a * a = 3 * 3 = 9然后 a *= 9,相当于 a = a * 9,即 a = 3 * 9 = 27最后 a -= 27,相当于 a = a - 27,即 a = 27 - 27 = 0所以 a = 0