void setup() {
  pinMode(0, INPUT_PULLUP);  // declaring GPIO0 as an INPUT pin.
  pinMode(2, OUTPUT); // declaring GPIO2 as an OUTPUT pin.
}

void loop() {
  // we use if() function to compare the GPIO0 reading state with the LOW state.
  // if the GPIO0 reading is LOW, light ON the LED on GPIO2 with LOW state.
  // else means, the GPIO0 reading is HIGH, light OFF the LED on GPIO2 with HIGH state. 
  int pbstatus = digitalRead(0);
  
  if (pbstatus == LOW) digitalWrite(2, HIGH);
  else digitalWrite(2, LOW);
}