Example of Sequencing 3 LEDs with nested arrays

sequencerArray.ino

int tempo = 250; // just the delay in milliseconds at the end of loop
int tracks = 3;
int trackPins[] = {
  12, 11, 10
};

int measure = 4;
int sequences[][4] = {
  { 1, 0, 1, 0 },
  { 1, 0, 0, 0 },
  { 1, 1, 1, 1 }
};

unsigned long counter = 0;

void setup() {
  for (int i = 0; i < tracks; i++) {
    pinMode(trackPins[i], OUTPUT);
  }
}

void loop() {
  int beat = counter % measure;
  for (int i = 0; i < tracks; i++) {
    if (sequences[i][beat]) {
      hit(trackPins[i]);
    }
  }

  counter++;
  delay(tempo);
}

void hit(int pin) {
  digitalWrite(pin, HIGH);
  delay(20);
  digitalWrite(pin, LOW);
}