const int digit1Pin = 8;
const int digit2Pin = 9;
const int segmentPins[] = {1, 2, 3, 4, 5, 6, 7, 0};

const byte digits[] = {
  B11000000,
  B11111001,
  B10100100,
  B10110000,
  B10011001,
  B10010010,
  B10000010,
  B11111000,
  B10000000,
  B10010000,
};

void setup() {
  pinMode(digit1Pin, OUTPUT);
  pinMode(digit2Pin, OUTPUT);

  for (int i = 0; i < 8; i++) {
    pinMode(segmentPins[i], OUTPUT);
  }
}

void loop() {
  for (int i = 9999; i >= 0; i--) {
    displayNumber(digit1Pin, i / 1000);
    delay(5);
    displayNumber(digit2Pin, (i / 100) % 10);
    delay(5);
  }
}

void displayNumber(int digitPin, int number) {
  digitalWrite(digit1Pin, LOW);
  digitalWrite(digit2Pin, LOW);

  for (int i = 0; i < 8; i++) {
    if (bitRead(digits[number], i)) {
      digitalWrite(segmentPins[i], HIGH);
    }else  {
      digitalWrite(segmentPins[i], LOW);
    }
  }
  digitalWrite(digitPin, HIGH);
}