const int numLEDs = 4;
const int GPIO_Pins[] = {0,1,2,3};
const int blinkRate = 500;
static bool flag = 1;
void setup() {
  // put your setup code here, to run once:
  for (int led=0;led<numLEDs;led++)
  {
    pinMode(GPIO_Pins[led],OUTPUT);
  }
}
void loop() {
  // put your main code here, to run repeatedly:
  for(int led=0;led<numLEDs;led++)
  {
    controlLEDs(led,flag);
  }
  delay(blinkRate);
  flag = !flag;
}
  void controlLEDs(int led, bool state)
  {
    if(state==1)
      digitalWrite(GPIO_Pins[led], HIGH);
    else
      digitalWrite(GPIO_Pins[led],LOW);
  }