const int LED[] = {11, 10, 9, 8, 7, 6, 5, 4};

void setup() {
  for (int i = 0; i < 8; i++) {
    pinMode(LED[i], OUTPUT);
    digitalWrite(LED[i], HIGH);
  }
}

void loop() {
  static bool clk = 0;
  for (int i = 0; i < 8; i++) {
    digitalWrite(LED[i], i % 2 == clk);
  }
  delay(250);
  clk = !clk;
}