What you have just learned in Chapter 4 are the most elementary operations we can do in Arduino: controlling digital output and reading digital input. If Arduino were some sort of human language, those would be two letters of its alphabet. Considering that there are just five letters in this alphabet, you can see how much more work we have to do before we can write Arduino poetry.
Now that you’ve learned how to use a pushbutton, you should know that there are many other very basic sensors that work according to the same principle:
Just like a pushbutton, but doesn’t automatically change state when released
A switch that opens when the temperature reaches a set ...