You've got a loop, you've got a condition and a boolean to check if he's touching the edge, and some statements to tell him to shout or to actually turn around.

我们有一个循环，通过一个条件和一个布尔值来判断,是否触到了边缘，还有一些语句,让它回头并咆哮。

哈佛公开课 - 计算机科学课程节选