// BCD IC A (ones digit)
const int bcdA_A = 22;
const int bcdA_B = 24;
const int bcdA_C = 26;
const int bcdA_D = 28;

// BCD IC B (tens digit)
const int bcdB_A = 30;
const int bcdB_B = 32;
const int bcdB_C = 34;
const int bcdB_D = 36;

// BCD IC C (hundreds digit)
const int bcdC_A = 38;
const int bcdC_B = 40;
const int bcdC_C = 42;
const int bcdC_D = 44;

// BCD IC D (thousands digit)
const int bcdD_A = 46;
const int bcdD_B = 48;
const int bcdD_C = 50;
const int bcdD_D = 52;

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

int counterValue = 0; 
boolean isCounting = false;
boolean lastActionIncrement = true; 
void setup() {
  // BCD IC A (ones digit)
  pinMode(bcdA_A, OUTPUT);
  pinMode(bcdA_B, OUTPUT);
  pinMode(bcdA_C, OUTPUT);
  pinMode(bcdA_D, OUTPUT);

  // BCD IC B (tens digit)
  pinMode(bcdB_A, OUTPUT);
  pinMode(bcdB_B, OUTPUT);
  pinMode(bcdB_C, OUTPUT);
  pinMode(bcdB_D, OUTPUT);

  // BCD IC C (hundreds digit)
  pinMode(bcdC_A, OUTPUT);
  pinMode(bcdC_B, OUTPUT);
  pinMode(bcdC_C, OUTPUT);
  pinMode(bcdC_D, OUTPUT);

  // BCD IC D (thousands digit)
  pinMode(bcdD_A, OUTPUT);
  pinMode(bcdD_B, OUTPUT);
  pinMode(bcdD_C, OUTPUT);
  pinMode(bcdD_D, OUTPUT);

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

  displayCounter();
}

void loop() {
  if (digitalRead(start_stop) == HIGH) {
    if (!isCounting) {
      // Start counting
      isCounting = true;
    } else {
      // Stop counting
      isCounting = false;
    }
    delay(200); 
  }

  if (isCounting) {
    if (lastActionIncrement) {
      counterValue++;
      if (counterValue > 9999) {
        counterValue = 0; 
      }
    } else {
      counterValue--;
      if (counterValue < 0) {
        counterValue = 9999; 
      }
    }
    displayCounter();
    delay(200); 
  }

  
  if (digitalRead(increment) == HIGH && !isButtonHeld(increment)) {
    lastActionIncrement = true; 
    if (!isCounting) {
      counterValue++;
      if (counterValue > 9999) {
        counterValue = 0; 
      }
      displayCounter();
    }
    delay(200); 
  }

 
  if (digitalRead(decrement) == HIGH && !isButtonHeld(decrement)) {
    lastActionIncrement = false; 
    if (!isCounting) {
      counterValue--;
      if (counterValue < 0) {
        counterValue = 9999; 
      }
      displayCounter();
    }
    delay(200); 
  }
}


bool isButtonHeld(int buttonPin) {
  
  int holdThreshold = 1000; 
  int holdDelay = 50; 
  int holdCount = holdThreshold / holdDelay;

  for (int i = 0; i < holdCount; i++) {
    delay(holdDelay);
    if (digitalRead(buttonPin) == LOW) {
      return false;
    }
  }
  return true;
}

void displayCounter() {
 
  int ones = counterValue % 10;
  int tens = (counterValue / 10) % 10;
  int hundreds = (counterValue / 100) % 10;
  int thousands = (counterValue / 1000) % 10;
  
switch (ones) {
    case 0:
        digitalWrite(bcdA_A, LOW);  
        digitalWrite(bcdA_B, LOW);  
        digitalWrite(bcdA_C, LOW);  
        digitalWrite(bcdA_D, LOW);  
        break;

    case 1:
        digitalWrite(bcdA_A, HIGH);  
        digitalWrite(bcdA_B, LOW);  
        digitalWrite(bcdA_C, LOW);  
        digitalWrite(bcdA_D, LOW); 
        break;

    case 2:
        digitalWrite(bcdA_A, LOW);  
        digitalWrite(bcdA_B, HIGH);  
        digitalWrite(bcdA_C, LOW);  
        digitalWrite(bcdA_D, LOW); 
        break;

    case 3:
        digitalWrite(bcdA_A, HIGH);  
        digitalWrite(bcdA_B, HIGH);  
        digitalWrite(bcdA_C, LOW);  
        digitalWrite(bcdA_D, LOW);  
        break;

    case 4:
        digitalWrite(bcdA_A, LOW);  
        digitalWrite(bcdA_B, LOW);  
        digitalWrite(bcdA_C, HIGH);  
        digitalWrite(bcdA_D, LOW);  
        break;

    case 5:
        digitalWrite(bcdA_A, HIGH);  
        digitalWrite(bcdA_B, LOW);  
        digitalWrite(bcdA_C, HIGH);  
        digitalWrite(bcdA_D, LOW); 
        break;

    case 6:
        digitalWrite(bcdA_A, LOW);  
        digitalWrite(bcdA_B, HIGH);  
        digitalWrite(bcdA_C, HIGH);  
        digitalWrite(bcdA_D, LOW);  
        break;

    case 7:
        digitalWrite(bcdA_A, HIGH);  
        digitalWrite(bcdA_B, HIGH);  
        digitalWrite(bcdA_C, HIGH);  
        digitalWrite(bcdA_D, LOW); 
        break;

    case 8:
        digitalWrite(bcdA_A, LOW); 
        digitalWrite(bcdA_B, LOW);  
        digitalWrite(bcdA_C, LOW);  
        digitalWrite(bcdA_D, HIGH);  
        break;

    case 9:
        digitalWrite(bcdA_A, HIGH);  
        digitalWrite(bcdA_B, LOW);  
        digitalWrite(bcdA_C, LOW);  
        digitalWrite(bcdA_D, HIGH); 
        break;
  }

  // Display tens digit
  switch (tens) {
    case 0:
        digitalWrite(bcdB_A, LOW);  
        digitalWrite(bcdB_B, LOW);  
        digitalWrite(bcdB_C, LOW);  
        digitalWrite(bcdB_D, LOW);  
        break;

    case 1:
        digitalWrite(bcdB_A, HIGH);  
        digitalWrite(bcdB_B, LOW);  
        digitalWrite(bcdB_C, LOW);  
        digitalWrite(bcdB_D, LOW); 
        break;

    case 2:
        digitalWrite(bcdB_A, LOW);  
        digitalWrite(bcdB_B, HIGH);  
        digitalWrite(bcdB_C, LOW);  
        digitalWrite(bcdB_D, LOW); 
        break;

    case 3:
        digitalWrite(bcdB_A, HIGH);  
        digitalWrite(bcdB_B, HIGH);  
        digitalWrite(bcdB_C, LOW);  
        digitalWrite(bcdB_D, LOW);  
        break;

    case 4:
        digitalWrite(bcdB_A, LOW);  
        digitalWrite(bcdB_B, LOW);  
        digitalWrite(bcdB_C, HIGH);  
        digitalWrite(bcdB_D, LOW);  
        break;

    case 5:
        digitalWrite(bcdB_A, HIGH);  
        digitalWrite(bcdB_B, LOW);  
        digitalWrite(bcdB_C, HIGH);  
        digitalWrite(bcdB_D, LOW); 
        break;

    case 6:
        digitalWrite(bcdB_A, LOW);  
        digitalWrite(bcdB_B, HIGH);  
        digitalWrite(bcdB_C, HIGH);  
        digitalWrite(bcdB_D, LOW);  
        break;

    case 7:
        digitalWrite(bcdB_A, HIGH);  
        digitalWrite(bcdB_B, HIGH);  
        digitalWrite(bcdB_C, HIGH);  
        digitalWrite(bcdB_D, LOW); 
        break;

    case 8:
        digitalWrite(bcdB_A, LOW); 
        digitalWrite(bcdB_B, LOW);  
        digitalWrite(bcdB_C, LOW);  
        digitalWrite(bcdB_D, HIGH);  
        break;

    case 9:
        digitalWrite(bcdB_A, HIGH);  
        digitalWrite(bcdB_B, LOW);  
        digitalWrite(bcdB_C, LOW);  
        digitalWrite(bcdB_D, HIGH); 
        break;
  }

  // Display hundreds digit
  switch (hundreds) {
    case 0:
        digitalWrite(bcdC_A, LOW);  
        digitalWrite(bcdC_B, LOW);  
        digitalWrite(bcdC_C, LOW);  
        digitalWrite(bcdC_D, LOW);  
        break;

    case 1:
        digitalWrite(bcdC_A, HIGH);  
        digitalWrite(bcdC_B, LOW);  
        digitalWrite(bcdC_C, LOW);  
        digitalWrite(bcdC_D, LOW); 
        break;

    case 2:
        digitalWrite(bcdC_A, LOW);  
        digitalWrite(bcdC_B, HIGH);  
        digitalWrite(bcdC_C, LOW);  
        digitalWrite(bcdC_D, LOW); 
        break;

    case 3:
        digitalWrite(bcdC_A, HIGH);  
        digitalWrite(bcdC_B, HIGH);  
        digitalWrite(bcdC_C, LOW);  
        digitalWrite(bcdC_D, LOW);  
        break;

    case 4:
        digitalWrite(bcdC_A, LOW);  
        digitalWrite(bcdC_B, LOW);  
        digitalWrite(bcdC_C, HIGH);  
        digitalWrite(bcdC_D, LOW);  
        break;

    case 5:
        digitalWrite(bcdC_A, HIGH);  
        digitalWrite(bcdC_B, LOW);  
        digitalWrite(bcdC_C, HIGH);  
        digitalWrite(bcdC_D, LOW); 
        break;

    case 6:
        digitalWrite(bcdC_A, LOW);  
        digitalWrite(bcdC_B, HIGH);  
        digitalWrite(bcdC_C, HIGH);  
        digitalWrite(bcdC_D, LOW);  
        break;

    case 7:
        digitalWrite(bcdC_A, HIGH);  
        digitalWrite(bcdC_B, HIGH);  
        digitalWrite(bcdC_C, HIGH);  
        digitalWrite(bcdC_D, LOW); 
        break;

    case 8:
        digitalWrite(bcdC_A, LOW); 
        digitalWrite(bcdC_B, LOW);  
        digitalWrite(bcdC_C, LOW);  
        digitalWrite(bcdC_D, HIGH);  
        break;

    case 9:
        digitalWrite(bcdC_A, HIGH);  
        digitalWrite(bcdC_B, LOW);  
        digitalWrite(bcdC_C, LOW);  
        digitalWrite(bcdC_D, HIGH); 
        break;
  }

  // Display thousands digit
  switch (thousands) {
    case 0:
        digitalWrite(bcdD_A, LOW);  
        digitalWrite(bcdD_B, LOW);  
        digitalWrite(bcdD_C, LOW);  
        digitalWrite(bcdD_D, LOW);  
        break;

    case 1:
        digitalWrite(bcdD_A, HIGH);  
        digitalWrite(bcdD_B, LOW);  
        digitalWrite(bcdD_C, LOW);  
        digitalWrite(bcdD_D, LOW); 
        break;

    case 2:
        digitalWrite(bcdD_A, LOW);  
        digitalWrite(bcdD_B, HIGH);  
        digitalWrite(bcdD_C, LOW);  
        digitalWrite(bcdD_D, LOW); 
        break;

    case 3:
        digitalWrite(bcdD_A, HIGH);  
        digitalWrite(bcdD_B, HIGH);  
        digitalWrite(bcdD_C, LOW);  
        digitalWrite(bcdD_D, LOW);  
        break;

    case 4:
        digitalWrite(bcdD_A, LOW);  
        digitalWrite(bcdD_B, LOW);  
        digitalWrite(bcdD_C, HIGH);  
        digitalWrite(bcdD_D, LOW);  
        break;

    case 5:
        digitalWrite(bcdD_A, HIGH);  
        digitalWrite(bcdD_B, LOW);  
        digitalWrite(bcdD_C, HIGH);  
        digitalWrite(bcdD_D, LOW); 
        break;

    case 6:
        digitalWrite(bcdD_A, LOW);  
        digitalWrite(bcdD_B, HIGH);  
        digitalWrite(bcdD_C, HIGH);  
        digitalWrite(bcdD_D, LOW);  
        break;

    case 7:
        digitalWrite(bcdD_A, HIGH);  
        digitalWrite(bcdD_B, HIGH);  
        digitalWrite(bcdD_C, HIGH);  
        digitalWrite(bcdD_D, LOW); 
        break;

    case 8:
        digitalWrite(bcdD_A, LOW); 
        digitalWrite(bcdD_B, LOW);  
        digitalWrite(bcdD_C, LOW);  
        digitalWrite(bcdD_D, HIGH);  
        break;

    case 9:
        digitalWrite(bcdD_A, HIGH);  
        digitalWrite(bcdD_B, LOW);  
        digitalWrite(bcdD_C, LOW);  
        digitalWrite(bcdD_D, HIGH); 
        break;
  }
}