I want the function, which is a little tool, a line of code I can include in my own programs and generally those tools live in sections two or three of the manual.

我想要一个函数，那是一个小工具，在我程序中可以包含的一行代码,通常这些工具在手册的第二节,或第三节。

哈佛公开课 - 计算机科学课程节选

So a function is just a little tool.

对，就是函数。

哈佛公开课 - 计算机科学课程节选

The standard library, that first line of code, it's not strictly necessary but any time you use a function, a tool that someone else wrote that lives in that so called library, you do need that include line as we'll see.

标准库函数--第一行代码，严格来说，不是每次都要写的，但是一旦你调用某个别人写，的函数，而这个函数又恰巧位于标准库里面,你就要像我们看到的这样，把它include进去。

哈佛公开课 - 计算机科学课程节选

Well, for a thing called main which itself is a function but a function I wrote, a tool I am writing at the moment not like printf which someone else wrote long ago, I have to say where does main start, where does main end, and I do that by using these curly braces.

至于这个名曰main的函数,由我们自己写的函数，也是一个工具,只不过由我们自己编写，而不是像printf那样已经由前人写好了,我们必须要说明main在哪开始，在哪结束，这样我们就要用到大括号了。

哈佛公开课 - 计算机科学课程节选