// Pin definitions for 74HC595
const int latchPin = 5; // Latch pin (RCLK)
const int clockPin = 6; // Clock pin (SCLK)
const int dataPin = 4;  // Data pin (DS)

// Inverted segment patterns for digits 0-9 for common anode
const byte digitSegments[10] = {
  B11111101, // 0
  B01100000, // 1
  B11011011, // 2
  B11110011, // 3
  B01100110, // 4
  B10110111, // 5
  B10111111, // 6
  B11100000, // 7
  B11111111, // 8
  B11110111  // 9
};

byte rfs =   B11111110; // Blank
byte rfd =   B00000000; // Blank
int i = 0;

#define buzzer 11
#define upButton  A5
#define downButton  A4
#define startButton  A3

void setup() {
 
  // Set buttons as input
  pinMode(upButton, INPUT);
  pinMode(downButton, INPUT);
  pinMode(startButton, INPUT);
 
  // Set 74HC595 pins as output
  pinMode(latchPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
 
  // Clear the screens
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, LSBFIRST, rfs);
  shiftOut(dataPin, clockPin, MSBFIRST, rfd);
  digitalWrite(latchPin, HIGH);
}

void loop() {
  if ((digitalRead(upButton) == HIGH) && (i != 9999)) {
    i++;
    delay(50);
  } else if ((digitalRead(downButton) == HIGH) && (i != 0)) {
    i--;
    delay(50);
  }
  displayNumber(i);
}
 
void displayNumber(int number) {
  for (int digit = 0; digit < 4; digit++) {
    digitalWrite(latchPin, LOW);
    shiftOut(dataPin, clockPin, LSBFIRST, digitSegments[number % 10]);
    shiftOut(dataPin, clockPin, MSBFIRST, 1 << digit);
    digitalWrite(latchPin, HIGH);
    number /= 10;
  }
}