答案是0,不断地变换小数点位置就可以了.
40.3×123.123123-0.123×40340.3403
=40.3×123.123123-123×40.3403403
=40.3×(123+0.123123)-123×（40.3+0.0403403）
消掉40.3×123后重复类似操作