Starting and stopping a sketch.

Projects Programming
4

PieterP:

    PushButton(uint8_t pin) // Constructor (executes when a PushButton object is created)

: pin(pin) { // remember the push button pin
      pinMode(pin, INPUT_PULLUP); // enable the internal pull-up resistor
    }

You should not place hardware related setup (like pinMode) in a constructor.
It could be run before the Arduino's init function, so it may not work.

Such initializations belong to a function often called begin() called from setup,
which is guaranteed to be run after init.