does Arduino analog pins need be declared?

Maybe is a stupid question, ask so because I tested many times, the sketch works well when declared the digit pin only.

for example:
inside void setup:

pinMode(12, INPUT);

digitalWrite(12, HIGH); or what else?
how can know set pin12 HIGH or LOW? if pin12 used for RC receiver signal in?

should I do:
pinMode(A2, INPUT);

digitalWrite(A2, HIGH);
if A2 used for a analog signal input?

Are the pins be used must be declared or better declared?

Thanks

To read a voltage on an analog pin you ‘do not’ need to use pinMode.

pinMode(12, INPUT); // set pin as a digital input pin.
digitalWrite(12, HIGH); // this turns on the internal pull-up resistor on pin 12.

The above two lines are the same as:
pinMode(12, INPUT_PULLUP);

larryd:
pinMode(12, INPUT); // set pin as a digital input pin.
digitalWrite(12, HIGH); // this turns on the internal pull-up resistor on pin 12.

The above two lines are the same as:
pinMode(12, INPUT_PULLUP);

Thank you,

the pin used as input for RC signal, should be set HIGH or LOW?

“the pin used as input for RC signal, ”

Please explain this more.

Perhaps you are looking to read a pin from an RC output. In this case I think you would use -
pinMode(12, INPUT);
digitalRead(12);