LED bar graph on pins 3 to 12, on an Arduino Uno

// An LED bar graph: ten bars on pins 3 to 12, one lit at a time.
//
//   pins 3..12 -> 220 ohm each -> the bar graph's ten anodes
//   the ten cathodes -> GND
//
// The pin numbers live in an array, so one for loop can visit them all.
// show(n) lights bar n and turns the other nine off; calling it for 0 to 9
// and back again makes the light run up the graph and down.

const int COUNT = 10;
const int PINS[COUNT] = {3, 4, 5, 6, 7, 8, 9, 10, 11, 12};

void show(int lit) {
  for (int i = 0; i < COUNT; i++) digitalWrite(PINS[i], i == lit ? HIGH : LOW);
  delay(100);
}

void setup() {
  for (int i = 0; i < COUNT; i++) pinMode(PINS[i], OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: LED bar graph on pins 3 to 12");
}

void loop() {
  for (int i = 0; i < COUNT; i++) show(i);
  for (int i = COUNT - 1; i >= 0; i--) show(i);
}