const int ledPins[] = {0,1,2,3}; 
static int arr[5];
const int numleds= 4;


void setup() {
  for(int i=0;i<numleds;i++) {
    pinMode(ledPins[i], OUTPUT);
    digitalWrite(ledPins[i],LOW);
  }
}
void loop() {
  
  for (int i = 1; i <= 15; i++) {
    binaryLED(i);

    delay(1000);
  }
  delay(2000);
}
void binaryLED(int num) {
  for (int i = 0; i<4;i++) {
    arr[i]=num%2;
    num=num/2;
    if(arr[i]==1)

       digitalWrite(ledPins[i],HIGH);
    else

    digitalWrite(ledPins[i],LOW);
  }
}