byte led[] = { 2, 3, 4, 5, 6, 7 };
byte current_led = 0;

void setup() {
  Serial.begin(9600);

  // put your setup code here, to run once:
  for (byte i = 0; i < sizeof(led); i++) {
    pinMode(led[i], OUTPUT);
  }

  Serial.println("--------------:" + String(sizeof(led)));
}


void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(led[current_led], HIGH);
  delay(50);

  current_led++;
  if (current_led > sizeof(led) - 1  ) {
    current_led = 0;
    for (byte i = 0; i < sizeof(led); i++) {
      digitalWrite(led[i], LOW);
    }
    delay(200);

    Serial.println("==========================");
  }

  Serial.println("led:" + String(led[current_led]));
}