const int bcdPins[4][4] = {
  {22, 24, 26, 28},  // BCD IC A
  {30, 32, 34, 36},  // BCD IC B
  {38, 40, 42, 44},  // BCD IC C
  {46, 48, 50, 52}   // BCD IC D
};

const int start_stop = 10;
const int increment = 11;
const int decrement = 12;

int counterValue = 0; // Stores counter
boolean isCounting = false;

void setup() {
  for (int i = 0; i < 4; ++i) {
    for (int j = 0; j < 4; ++j) {
      pinMode(bcdPins[i][j], OUTPUT);
    }
  }

  pinMode(start_stop, INPUT);
  pinMode(increment, INPUT);
  pinMode(decrement, INPUT);

  displayCounter();
}

void loop() {
  int startStopState = digitalRead(start_stop);
  int incrementState = digitalRead(increment);
  int decrementState = digitalRead(decrement);

  if (startStopState == HIGH) {
    isCounting = !isCounting;
    delay(250); // Debouncing delay
  }

  if (isCounting || incrementState == HIGH || decrementState == HIGH) {
    counterValue = (counterValue + (isCounting ? 1 : (incrementState == HIGH ? 1 : -1)) + 10000) % 10000;
    displayCounter();
    delay(250); // Debouncing delay
  }

  delay(100);
}

void displayDigit(int digit, int bcdPins[4]) {
  for (int i = 0; i < 4; ++i) {
    digitalWrite(bcdPins[i], (digit >> i) & 0x01);
  }
}

void displayCounter() {
  int ones = counterValue % 10;
  int tens = (counterValue / 10) % 10;
  int hundreds = (counterValue / 100) % 10;
  int thousands = counterValue / 1000;

  displayDigit(ones, bcdPins[0]);
  displayDigit(tens, bcdPins[1]);
  displayDigit(hundreds, bcdPins[2]);
  displayDigit(thousands, bcdPins[3]);
}