// Segment pins: a, b, c, d, e, f, g
int segPins[7] = {3, 4, 5, 6, 7, 8, 9};

volatile int counter = 0;  // must be volatile for interrupt

// 7-segment patterns for digits 0–9 (Common Cathode)
byte digits[10][7] = {
  {1,1,1,1,1,1,0}, // 0
  {0,1,1,0,0,0,0}, // 1
  {1,1,0,1,1,0,1}, // 2
  {1,1,1,1,0,0,1}, // 3
  {0,1,1,0,0,1,1}, // 4
  {1,0,1,1,0,1,1}, // 5
  {1,0,1,1,1,1,1}, // 6
  {1,1,1,0,0,0,0}, // 7
  {1,1,1,1,1,1,1}, // 8
  {1,1,1,1,0,1,1}  // 9
};

void setup() {
  // Set segment pins as output
  for (int i = 0; i < 7; i++) {
    pinMode(segPins[i], OUTPUT);
  }

  // Button pin with internal pull-up
  pinMode(2, INPUT_PULLUP);

  // Attach interrupt on pin 2
  attachInterrupt(digitalPinToInterrupt(2), countUp, FALLING);
}

void loop() {
  displayDigit(counter);

  // Simulate delay (interrupt still works!)
  delay(1000);
}

// Interrupt Service Routine (ISR)
void countUp() {
  counter++;
  if (counter > 9) counter = 0;
}

// Function to display digit
void displayDigit(int num) {
  for (int i = 0; i < 7; i++) {
    digitalWrite(segPins[i], digits[num][i]);
  }
}