#define N_GPIO 5
const uint8_t pins[N_GPIO] = {2, 3, 4, 5, 13};
const bool    mode[N_GPIO] = {INPUT, INPUT, OUTPUT, OUTPUT, OUTPUT};

void setup() {
  for(uint8_t i=0; i<N_GPIO; i++){
    pinMode(pins[i], mode[i]);
  }
}

void loop() {
  static uint32_t blinkTime = millis();
  if(millis() - blinkTime > 500){
    blinkTime = millis();
    digitalWrite(pins[4], !digitalRead(pins[4]));
  }
}