Type a digit: serial to a 74HC595 display (pins 11, 8 and 12), on an Arduino Uno

// Show a number: type a digit and a 74HC595 puts it on the display.
//
//   74HC595 DS -> pin 11   SH_CP -> pin 8   ST_CP -> pin 12
//   VCC and MR -> 5V   OE and GND -> GND
//   Q0..Q6 -> segments a..g (one 220 ohm on the display's common leg)
//
// Each digit is a byte with a bit per segment, bit 0 for a up to bit 6 for g.
// Serial.read() returns the character typed; subtracting '0' turns the
// character '7' into the number 7, which picks the pattern.

const int ST_CP = 12;
const int SH_CP = 8;
const int DS = 11;

const byte DIGITS[10] = {63, 6, 91, 79, 102, 109, 125, 7, 127, 111};

void write595(byte value) {
  digitalWrite(ST_CP, LOW);
  shiftOut(DS, SH_CP, MSBFIRST, value);
  digitalWrite(ST_CP, HIGH);
}

void setup() {
  pinMode(ST_CP, OUTPUT);
  pinMode(SH_CP, OUTPUT);
  pinMode(DS, OUTPUT);
  write595(DIGITS[0]);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: type a digit from 0 to 9");
}

void loop() {
  if (Serial.available() > 0) {
    char c = Serial.read();
    if (c >= '0' && c <= '9') {
      write595(DIGITS[c - '0']);
      Serial.print("showing ");
      Serial.println(c);
    }
  }
}