// roll no 31
void setup() {
pinMode(4, OUTPUT);
pinMode(8, OUTPUT);
pinMode(12, OUTPUT);
}

void loop() {

digitalWrite(4, HIGH); // red on
digitalWrite(8, LOW); // yellow off
digitalWrite(12, LOW); // green off
delay(500);
digitalWrite(4, LOW); // red off
digitalWrite(8, LOW); // yellow off
digitalWrite(12, HIGH); // green on
delay(500);
digitalWrite(4, LOW); // red off
digitalWrite(8, HIGH); // yellow on
digitalWrite(12, LOW); // green off
delay(500);
}