For uploading software, the Arduino has a serial port, and we can use it
to connect the Arduino to other devices, too (in Section 1.6, Compiling
and Uploading Programs, on page 38, you learn how to look up the
serial port your Arduino is connected to). In this section, we will use
it to control Arduino’s status LED using our computer’s keyboard. The
LED should be turned on when you press 1, and it should be turned
off when you press 2. Here’s all the code we need: