Is it safe to connect VCC to a data pin on Attiny chips? I'm trying to make a compact prototype with Attiny2313A, and want to connect VCC to pin 18 with a push button as in the picture. Is it safe? Or do I need a resistor there?
As mentioned by @chrisl, here you would need a pull-down resistor to make sure that pin was not high when the button was not pushed.
It is more typical to connect the button between the IO pin and ground since then you can use the built-in pull-up resistors to make sure the pin is high when the button is not pushed. (This chip only has built-in pull-ups, although some chips have pull-downs).