10.1.3 Return Statements Versus System Feedback

We mentioned back in Chapter 3 that drawing a line or printing text to the computer’s monitor doesn't count as "function output." That's because function output is done via the return keyword, and we can only return data that way. So, for example, "Make a red circle appear on the monitor” isn’t data; it’s a command. As such, there's a distinction between function output, which is just data that the computer passes around to itself, and system feedback, which is the manipulation of the computer’s peripheral devices to give information to a human user.