void a0_pin_state() {
  Serial.println(digitalRead(A0));
}

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(A0,INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(A0), a0_pin_state, CHANGE);
}

void loop() {

  // put your main code here, to run repeatedly:
  //Serial.println("");
  //Serial.println(digitalRead(A0));
  //Serial.println(analogRead(A0));
  delay(100);
}