byte digits[] = {0x7e, 0x30, 0x6d, 0x79, 0x33, 0x5b, 0x5f, 0x70, 0x7f, 0x7b};

int dataPin = 2;
int clockPin = 3;
int latchPin = 4;
int cathode1 = 5;
int cathode2 = 6;
int cathode3 = 7;

void setup() {
  // put your setup code here, to run once:
pinMode(dataPin, OUTPUT);
pinMode(clockPin, OUTPUT);
pinMode(latchPin, OUTPUT);
pinMode(cathode1, OUTPUT);
pinMode(cathode2, OUTPUT);
pinMode(cathode3, OUTPUT);

}

void loop() {
  // put your main code here, to run repeatedly:
   int num = 321;
      
      digitalWrite(latchPin, LOW);
      shiftOut(dataPin, clockPin, MSBFIRST, digits[num % 10]);
      digitalWrite(latchPin, HIGH);
      digitalWrite(cathode1, LOW);
      digitalWrite(cathode2, HIGH);
      digitalWrite(cathode3, HIGH);
      delay(10);

      digitalWrite(latchPin, LOW);
      shiftOut(dataPin, clockPin, MSBFIRST, digits[(num/10) % 10]);
      digitalWrite(latchPin, HIGH);
      digitalWrite(cathode1, HIGH);
      digitalWrite(cathode2, LOW);
      digitalWrite(cathode3, HIGH);
      delay(10);
      
      digitalWrite(latchPin, LOW);
      shiftOut(dataPin, clockPin, MSBFIRST, digits[(num/100) % 10]);
      digitalWrite(latchPin, HIGH);
      digitalWrite(cathode1, HIGH);
      digitalWrite(cathode2, HIGH);
      digitalWrite(cathode3, LOW);
      delay(10);
   
}