const int DATA_PIN = 2;
const int LATCH_PIN = 4;
const int CLOCK_PIN = 3;

const int PIN_DIGIT[3] = {12, 11, 10};
int digit[3] = {0, 0, 0};

int n = 0;
int seg = 0;
int segAnt = 0;

const int NUMS[10] = {252, 96, 218, 242, 102, 182, 190, 224, 254, 246};

void setup() {
    pinMode(DATA_PIN, OUTPUT);
    pinMode(LATCH_PIN, OUTPUT);
    pinMode(CLOCK_PIN, OUTPUT);
    for (int i = 0; i < 3; i++) {
        pinMode(PIN_DIGIT[i], OUTPUT);
    }
    Serial.begin(9600);
}

void loop() {
    if (n >= 999) {
        n = 0;
    } else {
        n++;
    }

    writeNum(n);
    seg = millis() / 100;
    if (seg != segAnt) {
        segAnt = seg;
    }
}

void writeNum(int num) {
    digit[0] = num / 100;
    digit[1] = (num % 100) / 10;
    digit[2] = num % 10;

    for (int i = 0; i < 3; i++) {
        if (i == 0 && digit[i] == 0) continue;
        if (i == 1 && digit[i] == 0 && digit[i-1] == 0) continue;
        ledOut(NUMS[digit[i]], i);
        digits(i);
        delay(300);
    }
}

void digits(int x) {
    for (int i = 0; i < 3; i++) {
        digitalWrite(PIN_DIGIT[i], LOW);
    }
    digitalWrite(PIN_DIGIT[x], HIGH);
}

void ledOut(int num, int dig) {
    shiftOut(DATA_PIN, CLOCK_PIN, LSBFIRST, ~num);
    digitalWrite(LATCH_PIN, LOW);
    digitalWrite(LATCH_PIN, HIGH);
}