Guess the number: IR remote and an I2C LCD, on an Arduino Uno

// Guess the number: the board thinks of a number, the remote guesses it.
//
//   IR receiver OUT -> pin 2   VCC -> 5V   GND -> GND
//   I2C LCD GND -> GND   VCC -> 5V   SDA -> A4   SCL -> A5
//
// Type up to two digits on the remote, then press PLAY/PAUSE to guess. The
// display shows the range the number is in, which closes in after every
// guess. Press CH (the middle button of the top row) to start a new game.
//
// Click buttons on the remote on the canvas.

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// The simulated remote speaks NEC, so only that decoder is compiled in.
#define DECODE_NEC
#include <IRremote.hpp>

// The remote's buttons by the command each one sends.
const char *keyOf(uint8_t command) {
  switch (command) {
    case 0x16: return "0";
    case 0x0C: return "1";
    case 0x18: return "2";
    case 0x5E: return "3";
    case 0x08: return "4";
    case 0x1C: return "5";
    case 0x5A: return "6";
    case 0x42: return "7";
    case 0x52: return "8";
    case 0x4A: return "9";
    case 0x45: return "CH-";
    case 0x46: return "CH";
    case 0x47: return "CH+";
    case 0x44: return "PREV";
    case 0x40: return "NEXT";
    case 0x43: return "PLAY/PAUSE";
    case 0x07: return "VOL-";
    case 0x15: return "VOL+";
    case 0x09: return "EQ";
    case 0x19: return "100+";
    case 0x0D: return "200+";
    default: return "";
  }
}

const int RECEIVER = 2;

LiquidCrystal_I2C lcd(0x27, 16, 2);
int target = 0;
int lower = 0;
int upper = 99;
int guess = 0;
int digits = 0;

void showRange(const char *line) {
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print(line);
  lcd.setCursor(0, 1);
  lcd.print(lower);
  lcd.print(" < ? < ");
  lcd.print(upper);
}

void newGame() {
  target = random(1, 99);
  lower = 0;
  upper = 99;
  guess = 0;
  digits = 0;
  showRange("Guess Number!");
  Serial.println("new game: a number from 1 to 98");
}

void setup() {
  Serial.begin(9600);
  lcd.init();
  lcd.backlight();
  randomSeed(analogRead(A0));
  IrReceiver.begin(RECEIVER, ENABLE_LED_FEEDBACK);
  Serial.println("Mokxi Uno: guess the number with the remote");
  newGame();
}

void loop() {
  if (!IrReceiver.decode()) return;
  bool repeat = IrReceiver.decodedIRData.flags & IRDATA_FLAGS_IS_REPEAT;
  const char *key = keyOf(IrReceiver.decodedIRData.command);
  IrReceiver.resume();
  if (repeat || key[0] == '\0') return;

  if (strcmp(key, "CH") == 0) {
    newGame();
  } else if (key[0] >= '0' && key[0] <= '9' && key[1] == '\0') {
    if (digits < 2) {
      guess = guess * 10 + (key[0] - '0');
      digits++;
    }
    lcd.clear();
    lcd.print("Your guess: ");
    lcd.print(guess);
  } else if (strcmp(key, "PLAY/PAUSE") == 0 && digits > 0) {
    Serial.print("guess ");
    Serial.println(guess);
    if (guess == target) {
      lcd.clear();
      lcd.print("You got it!");
      lcd.setCursor(0, 1);
      lcd.print("It was ");
      lcd.print(target);
      Serial.println("correct!");
    } else {
      if (guess > target && guess < upper) upper = guess;
      if (guess < target && guess > lower) lower = guess;
      showRange(guess > target ? "Too big" : "Too small");
    }
    guess = 0;
    digits = 0;
  }
}