Serial monitor drives eight LEDs (74HC595) on an Arduino Uno

// The serial monitor as a remote control: type 0 to 7 to light an LED.
//
//   74HC595 DS (pin 14)    -> Uno pin 12   (data)
//   74HC595 SHCP (pin 11)  -> Uno pin 9    (clock)
//   74HC595 STCP (pin 12)  -> Uno pin 11   (latch)
//   74HC595 VCC and MR -> 5V      GND and OE -> GND
//   Q0 to Q7 -> eight LEDs, each through 220 ohm to GND
//
// Serial.read() takes one character off what you typed. The characters '0' to
// '7' are not the numbers 0 to 7 but codes 48 to 55, so the sketch subtracts
// '0' to turn one into the other. Type x to put every LED out.
//
// Type into the box under the serial monitor and press Enter.

const int DATA_PIN = 12;
const int CLOCK_PIN = 9;
const int LATCH_PIN = 11;

byte leds = 0;

void show(byte value) {
  digitalWrite(LATCH_PIN, LOW);
  shiftOut(DATA_PIN, CLOCK_PIN, MSBFIRST, value);  // bit 0 lands on Q0
  digitalWrite(LATCH_PIN, HIGH);
}

void setup() {
  pinMode(DATA_PIN, OUTPUT);
  pinMode(CLOCK_PIN, OUTPUT);
  pinMode(LATCH_PIN, OUTPUT);
  show(leds);
  Serial.begin(9600);
  Serial.println("Enter an LED number, 0 to 7, or x to clear");
}

void loop() {
  if (Serial.available() == 0) return;
  char ch = Serial.read();
  if (ch >= '0' && ch <= '7') {
    int led = ch - '0';
    bitSet(leds, led);
    show(leds);
    Serial.print("Turned on LED ");
    Serial.println(led);
  } else if (ch == 'x' || ch == 'X') {
    leds = 0;
    show(leds);
    Serial.println("Cleared");
  }
}