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Input and Output

Comic by xkcd.

The term "i/o" stands for input/output. In the context of writing programs, i/o refers to anything in our code that interacts with the "outside world." And "outside world" just means anything that's not stored in our application's memory (like variables).

Examples of I/O

Reading from or writing to a file on the hard drive
Accessing the internet
Reading from or writing to a database
Even simply printing to the console!!

All i/o is a form of "side effect."

Assignment

In Doc2Doc, we frequently need to change the casing of some text. For example:

TitleCase

Every Day Once A Day Give Yourself A Present

LowerCase

every day once a day give yourself a present

UpperCase

EVERY DAY ONCE A DAY GIVE YOURSELF A PRESENT

There's an issue in the convert_case function; our test suite can't test its behavior because it's printing to the console (eww, a side effect) instead of returning a value. Fix the function so that it returns the correct value instead of printing it.