Three-digit voltmeter on an Arduino Uno

// Three-digit voltmeter: a potentiometer's wiper on A0, shown as 0.00 to 5.00
// on a bare three-digit display that the sketch multiplexes.
//
//   segments A B C D E F G DP -> pins 2 to 9, each through its own 220 ohm
//   digits DIG1 DIG2 DIG3     -> pins 10, 11 and 12
//   potentiometer             -> 5V, A0 (the wiper), GND
//
// Common cathode: a digit is on while its common is LOW. The point after the
// first digit is that digit's DP segment.

const uint8_t SEGMENT_PINS[8] = {2, 3, 4, 5, 6, 7, 8, 9};
const uint8_t DIGIT_PINS[3] = {10, 11, 12};
const uint8_t FONT[10] = {0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x6F};
const uint8_t POINT = 0x80;

int hundredths = 0;  // the voltage in hundredths of a volt
unsigned long lastRead = 0;

void showDigit(uint8_t which, uint8_t pattern) {
  for (uint8_t i = 0; i < 3; i++) digitalWrite(DIGIT_PINS[i], HIGH);
  for (uint8_t s = 0; s < 8; s++) digitalWrite(SEGMENT_PINS[s], (pattern >> s) & 1);
  digitalWrite(DIGIT_PINS[which], LOW);
  delay(4);
}

void setup() {
  for (uint8_t i = 0; i < 8; i++) pinMode(SEGMENT_PINS[i], OUTPUT);
  for (uint8_t i = 0; i < 3; i++) {
    pinMode(DIGIT_PINS[i], OUTPUT);
    digitalWrite(DIGIT_PINS[i], HIGH);
  }
}

void loop() {
  if (millis() - lastRead >= 100) {
    lastRead = millis();
    // 1023 is 5.00 V: scale the reading to hundredths, rounded.
    hundredths = (int)((analogRead(A0) * 500L + 511) / 1023);
  }
  showDigit(0, FONT[hundredths / 100] | POINT);
  showDigit(1, FONT[(hundredths / 10) % 10]);
  showDigit(2, FONT[hundredths % 10]);
}