0.4 - 0.3 == 0.1是true？？false

你注意过了么？

 

此处的运算结果是false。

 

这个是ruby上给的解释。哈哈，见识了。

 

Float objects have plenty of precision and can approximate 0.1 very well, 
but the fact that this number cannot be represented exactly leads to problems. 
Consider the following simple Ruby expression:

0.4 - 0.3 == 0.1    # Evaluates to false in most implementations

Because of rounding error, the difference between the approximations of 0.4 and 0.3 is 
not quite the same as the approximation of 0.1. This problem is not specific to Ruby: C, 
Java,JavaScript, and all languages that use IEEE-754 floating-point numbers suffer 
from it as well.