My assumption is, that if I declare a pin as input, it is also grounded.
You don't need the resistor
question about connecting two digital pins (Output and Input)
My assumption is, it isn't grounded.
Why do I have to declare a pin as output or input at all?Because you can read and write to an input and output pin... :|
Note that the pullup resistors provide enough current to dimly light an LED
In all tutorials the guys are using a resister (10kOhm) against electric noise.
It doesn't provide the "full" current...