void loop(){
  uint16_t i;
  for(i=0; i<strip.numPixels(); i++) {
    uint32_t white = strip.Color(255, 255, 255);
    strip.setPixelColor(i, white);
    strip.show();
    delay(500);

    if (i == strip.numPixels() -1 ){
      all_red();
    }

  }
}

void all_red(){
  uint32_t red = strip.Color(255, 0, 0);
  for(j=0; j<strip.numPixels(); j++){
  strip.setPixelColor(j, red);
  }
  strip.show();