So the double quote says here comes the input.

双引号代表在这里填上想要输入的东西。

哈佛公开课 - 计算机科学课程节选

Someone-- or someone had to implement, had to write a tool called printf that itself takes input between quotes and produces as output some characters on the screen.

需要有人去实现，这个printf函数,以双引号间的信息为输入,输出相应字母到屏幕上。

哈佛公开课 - 计算机科学课程节选