Moving dot - FastLED

void loop()
{
    // Move a single dot along a strip

    for(int led_number = 0; led_number < NUM_LEDS; led_number++)
    {
        // Turn our current led ON, then show the leds
        leds[led_number] = CRGB::Red;

        // Show the leds (only one of which is has a color set, from above
        // Show turns actually turns on the LEDs
        FastLED.show();

        // Wait a little bit - this will dictate speed
        delay(30);

        // Now set our current led back to black,
        // but we wont show that until the next loop around.
        leds[led_number] = CRGB::Black;
    }