通常我们用符号s来表示弧长。

So, the usual notation that we will have is for arc length.

youdao

其种类很多，但基本的理念是在变量名的开始添加一个标记以表示其类型（例如，所有无符号长型变量都以 ul 开头）。

There are lots of flavors of this, but the basic idea is that you put a tag at the beginning of a variable name saying what type it is. (So all unsigned long variables begin with ul, etc.)

youdao

我不知道为何要用s来表示弧长，这只是一个常用的符号。

I'm not quite sure how you get an out of this, but it's the usual notation.

youdao