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

// LCD setup
LiquidCrystal_I2C lcd(0x27, 16, 2);

// Keypad setup
const byte ROWS = 4; // four rows
const byte COLS = 4; // four columns
char keys[ROWS][COLS] = {
  {'1', '2', '3', '+'},
  {'4', '5', '6', '-'},
  {'7', '8', '9', '*'},
  {'C', '0', '=', '/'}
};
byte rowPins[ROWS] = {2, 4, 5, 0}; // connect to the row pinouts of the keypad
byte colPins[COLS] = {25, 26, 27, 32}; // connect to the column pinouts of the keypad
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

float num1 = 0;
float num2 = 0;
char operation = ' ';

void setup() {
  lcd.init();
  lcd.backlight();
  lcd.setCursor(2,0);
  lcd.print(" Calculator!");
  delay(5000);
  lcd.clear();
}

void loop() {
  char key = keypad.getKey();
  
  if (key) {
    if (key >= '0' && key <= '9') {
      lcd.print(key);
      if (operation == ' ') {
        num1 = num1 * 10 + (key - '0');
      } else {
        num2 = num2 * 10 + (key - '0');
      }
    } else if (key == 'C') {
      lcd.clear();
      num1 = 0;
      num2 = 0;
      operation = ' ';
    } else if (key == '=' && operation != ' ') {
      float result = 0;
      switch (operation) {
        case '+': result = num1 + num2; break;
        case '-': result = num1 - num2; break;
        case '*': result = num1 * num2; break;
        case '/': 
          if (num2 != 0) result = num1 / num2; 
          else lcd.print("Err"); // Handle division by zero
          break;
      }
      lcd.print(" = ");
      lcd.print(result);
      num1 = result; // Allow chaining operations
      num2 = 0;
      operation = ' ';
    } else {
      operation = key; // Save the operation
      lcd.print(" ");
      lcd.print(operation);
    }
  }
}