Memory math game on an LCD and an IR remote, on an Arduino Uno

// Memory math: a sum flashes on the LCD for two seconds, then you key in the
// answer on the IR remote from memory.
//
//   LCD RS -> pin 2   E -> A3   D4 -> pin 8   D5 -> pin 7   D6 -> A2   D7 -> pin 4
//   IR receiver OUT -> pin 12
//   RGB LED red -> pin 9, green -> pin 6, blue -> pin 5, each through 220 ohm
//   passive buzzer -> pin 3
//
// Press 1, 2 or 3 on the remote to pick a level:
//   1  remember a number
//   2  remember an addition and work it out
//   3  remember a multiplication and work it out
// Each round has five questions. Type the answer with the number keys, then:
//   VOL-     (the "+" key on the simulated handset) to send it
//   EQ       (the "100+" key) to rub out the last digit
//   ST/REPT  (the "200+" key) to clear the line
// Both handsets send the same codes; only the printing on the keys differs.

#define DECODE_NEC
#include <IRremote.hpp>
#include <LiquidCrystal.h>

LiquidCrystal lcd(2, A3, 8, 7, A2, 4);  // RS, E, D4, D5, D6, D7

const int RECEIVER_PIN = 12;
const int RED_PIN = 9;
const int GREEN_PIN = 6;
const int BLUE_PIN = 5;
const int BUZZER = 3;
const int QUESTIONS = 5;

const byte KEY_OK = 0x15;
const byte KEY_BACK = 0x19;
const byte KEY_CLEAR = 0x0D;
const byte DIGIT_KEYS[10] = {0x16, 0x0C, 0x18, 0x5E, 0x08, 0x1C, 0x5A, 0x42, 0x52, 0x4A};

void showTyped();

int level = 0;
int question = 0;
int score = 0;
long answer = 0;
char typed[8];
int typedLength = 0;

void color(int r, int g, int b) {
  analogWrite(RED_PIN, r);
  analogWrite(GREEN_PIN, g);
  analogWrite(BLUE_PIN, b);
}

// The remote's next key press, or -1 if none (repeats are ignored).
int nextKey() {
  if (!IrReceiver.decode()) return -1;
  bool repeat = IrReceiver.decodedIRData.flags & IRDATA_FLAGS_IS_REPEAT;
  int command = IrReceiver.decodedIRData.command;
  IrReceiver.resume();
  return repeat ? -1 : command;
}

int digitOf(int key) {
  for (int d = 0; d < 10; d++) {
    if (DIGIT_KEYS[d] == key) return d;
  }
  return -1;
}

void showMenu() {
  level = 0;
  color(0, 0, 60);
  lcd.clear();
  lcd.print("Memory math");
  lcd.setCursor(0, 1);
  lcd.print("Level 1, 2 or 3?");
  Serial.println("pick a level: 1, 2 or 3");
}

void ask() {
  long a, b;
  lcd.clear();
  lcd.print("Q");
  lcd.print(question + 1);
  lcd.print(" remember:");
  lcd.setCursor(0, 1);
  if (level == 1) {
    answer = random(1000, 100000);
    lcd.print(answer);
  } else if (level == 2) {
    a = random(10, 1000);
    b = random(10, 1000);
    answer = a + b;
    lcd.print(a);
    lcd.print(" + ");
    lcd.print(b);
  } else {
    a = random(2, 100);
    b = random(2, 100);
    answer = a * b;
    lcd.print(a);
    lcd.print(" x ");
    lcd.print(b);
  }
  Serial.print("question ");
  Serial.println(question + 1);
  delay(2000);
  typedLength = 0;
  typed[0] = '\0';
  showTyped();
}

void showTyped() {
  lcd.clear();
  lcd.print("Your answer:");
  lcd.setCursor(0, 1);
  lcd.print(typed);
}

void check() {
  long given = atol(typed);
  lcd.clear();
  if (typedLength > 0 && given == answer) {
    score++;
    lcd.print("Right!");
    color(0, 160, 0);
    tone(BUZZER, 880, 300);
    Serial.println("right");
  } else {
    lcd.print("Not quite. It was");
    lcd.setCursor(0, 1);
    lcd.print(answer);
    color(160, 0, 0);
    tone(BUZZER, 110, 500);
    Serial.println("wrong");
  }
  delay(1500);
  color(0, 0, 0);
  question++;
  if (question < QUESTIONS) {
    ask();
    return;
  }
  lcd.clear();
  lcd.print("Round over");
  lcd.setCursor(0, 1);
  lcd.print("Score: ");
  lcd.print(score);
  lcd.print(" of 5");
  Serial.print("score ");
  Serial.println(score);
  for (int i = 0; i < score; i++) {
    tone(BUZZER, 523 + 131 * i, 150);
    delay(200);
  }
  delay(2000);
  showMenu();
}

void setup() {
  pinMode(RED_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  pinMode(BLUE_PIN, OUTPUT);
  Serial.begin(9600);
  lcd.begin(16, 2);
  IrReceiver.begin(RECEIVER_PIN);
  randomSeed(analogRead(A0));
  Serial.println("Mokxi Uno: memory math on the IR remote.");
  showMenu();
}

void loop() {
  int key = nextKey();
  if (key < 0) return;
  int d = digitOf(key);
  if (level == 0) {
    if (d >= 1 && d <= 3) {
      level = d;
      question = 0;
      score = 0;
      Serial.print("level ");
      Serial.println(level);
      ask();
    }
    return;
  }
  if (d >= 0 && typedLength < 7) {
    typed[typedLength++] = '0' + d;
    typed[typedLength] = '\0';
    showTyped();
  } else if (key == KEY_BACK && typedLength > 0) {
    typed[--typedLength] = '\0';
    showTyped();
  } else if (key == KEY_CLEAR) {
    typedLength = 0;
    typed[0] = '\0';
    showTyped();
  } else if (key == KEY_OK) {
    check();
  }
}