const byte ledPin1 = 2;
const byte ledPin2 = 3;
const byte ledPin3 = 4;
const byte ledPin4 = 5;

void setup() {
  pinMode(ledPin1, OUTPUT);
  pinMode(ledPin2, OUTPUT);
  pinMode(ledPin3, OUTPUT);
  pinMode(ledPin4, OUTPUT);
}

void displayBinary(byte number) {
  byte number_change = number;
  
  digitalWrite(ledPin1, number_change % 2);
  number_change = number_change / 2;
  
  digitalWrite(ledPin2, number_change % 2);
  number_change = number_change / 2;
  
  digitalWrite(ledPin3, number_change % 2);
  number_change = number_change / 2;
  
  digitalWrite(ledPin4, number_change % 2);
}

void loop() {
  for(byte counter = 0; counter < 16; counter++) {
    displayBinary(counter);
    delay(1000);
  }
}