Countdown digit on an Arduino Uno

// Countdown digit: a 74HC595 drives a one-digit seven-segment display.
//
//   74HC595   DS -> pin 4, SHCP (clock) -> pin 5, STCP (latch) -> pin 6
//             Q0 to Q6 -> segments A to G, each through its own 220 ohm
//   display   common cathode, COM -> GND
//
// Eight pins for one digit is a lot of an Uno. Through the 74HC595 it is three
// pins, however many segments there are: the sketch sends one byte, a bit per
// segment, and the latch shows all eight at once.
//
// The table holds one byte per digit, bit 0 for segment A up to bit 6 for G.
// The display counts down from 9 to 0, one number a second, and starts again.

const int DATA = 4;
const int CLOCK = 5;
const int LATCH = 6;

//                    gfedcba
const byte DIGITS[10] = {
    0b00111111,  // 0
    0b00000110,  // 1
    0b01011011,  // 2
    0b01001111,  // 3
    0b01100110,  // 4
    0b01101101,  // 5
    0b01111101,  // 6
    0b00000111,  // 7
    0b01111111,  // 8
    0b01101111,  // 9
};

void show(int digit) {
  digitalWrite(LATCH, LOW);
  shiftOut(DATA, CLOCK, MSBFIRST, DIGITS[digit]);
  digitalWrite(LATCH, HIGH);
}

void setup() {
  pinMode(DATA, OUTPUT);
  pinMode(CLOCK, OUTPUT);
  pinMode(LATCH, OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: countdown digit");
}

void loop() {
  for (int digit = 9; digit >= 0; digit--) {
    show(digit);
    Serial.print("showing ");
    Serial.println(digit);
    delay(1000);
  }
}