//Traffic Light Demo with Millis
const int red=2;
const int yellow=3;
const int green=4;

//duration
unsigned long redDuration=5000;
unsigned long yellowDuration=2000;
unsigned long greenDuration=5000;

unsigned long prevMillis=0;
int currentLight=red;

void setup() {
  pinMode(red, OUTPUT);
  pinMode(yellow, OUTPUT);
  pinMode(green, OUTPUT);
}

void loop() 
{
  unsigned long currentMillis=millis();
  if(currentMillis-prevMillis>getDuration(currentLight))
  {
    prevMillis=currentMillis;
    switchLight();
  }

}
//function get duration
unsigned long getDuration(int currentLight)
{
  if(currentLight==red)
  return redDuration;
  else if(currentLight==yellow)
  return yellowDuration;
  else if(currentLight==green)
  return greenDuration;
}

//function Switch Light
void switchLight()
{
  digitalWrite(currentLight, LOW);
  if(currentLight==red){
    currentLight=green;
  }
  else
  if(currentLight==green){
    currentLight=yellow;
  }
  else
  currentLight=red;
  digitalWrite(currentLight,HIGH);
}