#include <Adafruit_NeoPixel.h>

int N_LED = 40;
int din = 12;
Adafruit_NeoPixel ring = Adafruit_NeoPixel(N_LED, din);

void setup() {
  ring.begin();
}

void loop() {
  for (int i = 0; i < N_LED; i++) {
    if (i < 10) {
      ring.setPixelColor(i, ring.Color(255, 0, 0));
    } else if (i < 20) {
      ring.setPixelColor(i, ring.Color(0, 255, 0));
    } else if (i < 30) {
      ring.setPixelColor(i, ring.Color(0, 0, 255));
    } else {
      ring.setPixelColor(i, ring.Color(255, 255, 255));
    }

    ring.show();
    delay(1000);
  }
}