#define num_changing_leds 2

uint8_t red_led = 11;
uint8_t green_led = 2;
uint8_t yellow_led = 7;
uint8_t changing_leds[num_changing_leds] = {red_led, green_led};
uint8_t index_cur = 0;

void setup() {
  pinMode(red_led, OUTPUT);
  pinMode(green_led, OUTPUT);
  pinMode(yellow_led, OUTPUT);
}

void loop() {
  digitalWrite(yellow_led, LOW);
  digitalWrite(changing_leds[index_cur], HIGH);
  delay(10000);
  digitalWrite(changing_leds[index_cur], LOW);
  digitalWrite(yellow_led, HIGH);
  delay(2000);
  index_cur = (index_cur + 1) % num_changing_leds;
}