const int btnMinus = 2;
const int btnPlus = 3;
const int data = 4;
const int latch = 5;
const int clock = 6;

const byte digits[] {
// ABCDEFGDp
// ||||||||
  B11111100, // 0
  B01100000, // 1
  B11011010, // 2
  B11110010, // 3
  B01100110, // 4
  B10110110, // 5
  B10111110, // 6
  B11100000, // 7
  B11111110, // 8
  B11110110, // 9
  B11101110, // A
  B00111110, // B
  B10011100, // C
  B01111010, // D
  B10011110, // E
  B10001110, // F
};

int count;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(btnMinus, INPUT);
  pinMode(btnPlus, INPUT);
  pinMode(data, OUTPUT);
  pinMode(latch, OUTPUT);
  pinMode(clock, OUTPUT);

  digitalWrite(latch, HIGH);

  count = 0;

  Serial.print("Count : ");
  Serial.println(count);

  displayCount();
}

void loop() {
  // put your main code here, to run repeatedly:
  if (digitalRead(btnMinus) == HIGH) {
    if (count <= 0) {
      count = 255;
    } else {
      count--;
    }
    delay(250);
    displayCount();
  }

  if (digitalRead(btnPlus) == HIGH) {
    if (count >= 255) {
      count = 0;
    } else {
      count++;
    }
    delay(250);
    displayCount();
  }
}

void displayCount() {
  Serial.print("Count : ");
  Serial.println(count);
  byte tens = count % 256 / 16;
  byte units = count % 16;
  sendCount(digits[tens], digits[units]);
}

void sendCount(byte tens, byte units) {
  digitalWrite(latch, LOW);
  shiftOut(data, clock, LSBFIRST, units);
  shiftOut(data, clock, LSBFIRST, tens);
  digitalWrite(latch, HIGH);
}