#define yellow 4
#define red 5
#define blue 6

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(yellow, OUTPUT);
  pinMode(red, OUTPUT);
  pinMode(blue, OUTPUT);
int i = 0;
  while (i < 10) {
    int k=i%3;
    Serial.print("i = ");Serial.print(i);
    Serial.print("   k(i%3) = ");Serial.println(k);
    switch(k)
    {
      case 0:{
        digitalWrite(yellow, HIGH);
        delay(500);
        digitalWrite(yellow, LOW);
        delay(500);
      }
      break;
      case 1:{
        digitalWrite(red, HIGH);
        delay(500);
        digitalWrite(red, LOW);
        delay(500);
      }
      break;
      case 2:{
        digitalWrite(blue, HIGH);
        delay(500);
        digitalWrite(blue, LOW);
        delay(500);
      }
      break;
    }
    i++;
  }
  }


void loop() {
  // put your main code here, to run repeatedly:

}