If I want a copy of the string, I've got to whip out my week 1 skills of just iterating with a four loop from left to right and make copies of those characters.

我需要那个字符串的一个拷贝，我使用,第一周的技巧，从左到右做四次迭代,然后复制这4个字符。

哈佛公开课 - 计算机科学课程节选

Well, this question mark becomes an O, this question mark becomes an O, and then the loop terminates 0 1 2 because it's iterating from zero to N so that's zero, 1, 2 and the length of the string is 3 so the loop terminates, but I remember that I needed to have this special sentinel value so I'm just going to put it there manually.

嗯，这个问号变成了，这个问号变成了0，然后循环结束了,以为迭代从0到N，那就是，字符串的长度是3，然后循环就结束了，但是我记得我需要这个特殊的标记值,所以需要手动的加上它。

哈佛公开课 - 计算机科学课程节选