Default digital/analog pin state - input or output? (do unused pins need to be grounded to prevent floating inputs)

[sterretje]

@billybob884

So should I set all unused pins to 'output' mode so they don't need to be pulled high/low?

Setting an unused pin to output if not needed is, in my opinion, dangerous. If you short the pin by accident, you can damage it.

If you don't want them to float, use INPUT_PULLUP. Else leave them.