// CONNECT CN2 to CN8

constexpr uint8_t dataPin = 4;    //DS
constexpr uint8_t clockPin = 2;   //SHCP
constexpr uint8_t latchPin = 3;   //STCP

uint8_t digits[10] = {
  0b00111111, //0
  0b00000110, //1 
  0b01011011, //2
  0b01001111, //3 
  0b01100110, //4
  0b01101101, //5
  0b01111101, //6
  0b00000111, //7
  0b01111111, //8
  0b01101111  //9
};

void shiftOut(uint8_t value) {
  for (uint8_t i = 0; i < 8; ++i) {
    // Extract the bit to send based on the bit order
    bool bitToSend = (value >> (7 - i)) & 0x01;

    // Send the bit out
    digitalWrite(dataPin, bitToSend);
    digitalWrite(clockPin, HIGH);
    digitalWrite(clockPin, LOW);
  }
}

void displayDigit(int number) {
  shiftOut(digits[number%10]);
  shiftOut(digits[number/10]);
  
  digitalWrite(latchPin, HIGH); 
  digitalWrite(latchPin, LOW);
}

void setup() {

  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
  pinMode(latchPin, OUTPUT);
  
  // set pins low
  digitalWrite(clockPin, LOW);
  digitalWrite(dataPin, LOW);
  digitalWrite(latchPin, LOW);
}

void loop() {
  for(uint8_t i=0; i<99; i++) {
    displayDigit(i);
    delay(300);
  }
}