Простой калькулятор на Arduino + клавиатура 4×4 + LCD 1602 I2C

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

LiquidCrystal_I2C lcd(0x27,16,2);  // адрес найдите сканером I2C

const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
  {'1','2','3','+'},
  {'4','5','6','-'},
  {'7','8','9','*'},
  {'C','0','=','/'}
};
byte rowPins[ROWS] = {9,8,7,6};
byte colPins[COLS] = {5,4,3,2};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

float num1 = 0, num2 = 0, result = 0;
char action = 0;
bool finished = false;

void setup() {
  lcd.init();
  lcd.backlight();
  lcd.print("Простой кальк.");
  delay(2000);
  lcd.clear();
}

void loop() {
  char key = keypad.getKey();

  if (key) {
    if (key >= '0' && key <= '9') {
      if (!action) num1 = num1 * 10 + (key - '0');
      else       num2 = num2 * 10 + (key - '0');
      showInput();
    }

    if (key == '+' || key == '-' || key == '*' || key == '/') {
      action = key;
      showInput();
    }

    if (key == '=') {
      calculate();
      finished = true;
      showResult();
    }

    if (key == 'C') {
      num1 = num2 = result = 0;
      action = 0;
      finished = false;
      lcd.clear();
    }
  }
}

void showInput() {
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print(num1);
  if (action) lcd.print(action);
  if (action) lcd.print(num2);
}

void calculate() {
  switch(action) {
    case '+': result = num1 + num2; break;
    case '-': result = num1 - num2; break;
    case '*': result = num1 * num2; break;
    case '/': result = num1 / num2; break;
  }
}

void showResult() {
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print(num1);
  lcd.print(action);
  lcd.print(num2);
  lcd.print("=");
  lcd.setCursor(0,1);
  lcd.print(result, 2);
}