const int numLEDs = 4;
const int GPIO_Pins[] = {2, 6, 10, 14};
const int runRate = 500;
void setup() {
for (int led = 0; led < numLEDs; led++) {
pinMode(GPIO_Pins[led], OUTPUT);
}
} 
void loop() {
controlLEDs(runRate);
}
void controlLEDs(int runRate) {
// Blink the first 2 LEDs while the last 2 are off
for (int led = 0; led < numLEDs / 2; led++) {
digitalWrite(GPIO_Pins[led], HIGH);
} 

delay(runRate);
for (int led = 0; led < numLEDs / 2; led++) {
digitalWrite(GPIO_Pins[led], LOW);
}
delay(runRate);
// Blink the last 2 LEDs while the first 2 are off
for (int led = numLEDs / 2; led < numLEDs; led++) {
digitalWrite(GPIO_Pins[led], HIGH);
}
delay(runRate);
for (int led = numLEDs / 2; led < numLEDs; led++) {
digitalWrite(GPIO_Pins[led], LOW);
}
delay(runRate); 
}