I just want to make mention of this in case there's ever doubt, generally parentheses do solve your problem as an arithmetic but do realize this is some lower level details we'll come back to over time.

是想告诉大家如果你对某些式子的前后运算关系不确定，就加上括号,这都是一些小细节,我们以后还是会再提到的。

哈佛公开课 - 计算机科学课程节选