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

const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};
byte rowPins[ROWS] = {9, 8, 7, 6};    // Connect to the row pinouts of the keypad
byte colPins[COLS] = {5, 4, 3, 2};    // Connect to the column pinouts of the keypad

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);
LiquidCrystal_I2C lcd(0x27, 16, 2);

String input = "";
char operation = 0;
float num1, num2, result;

void setup() {
  lcd.begin(16, 2);
  lcd.print("Calculator Ready");
  delay(2000);
  lcd.clear();
}

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

  if (key) {
    if (key >= '0' && key <= '9') {  // If key is a number
      input += key;
      lcd.setCursor(0, 0);
      lcd.print(input);
    } 
    else if (key == 'A' || key == 'B' || key == 'C' || key == 'D') {  // If key is an operator
      if (input.length() > 0) {
        num1 = input.toFloat();
        input = "";
        operation = key;
        lcd.setCursor(0, 1);
        lcd.print(key);
      }
    } 
    else if (key == '#') {  // Equals key
      if (input.length() > 0) {
        num2 = input.toFloat();
        switch (operation) {
          case 'A': result = num1 + num2; break;
          case 'B': result = num1 - num2; break;
          case 'C': result = num1 * num2; break;
          case 'D': result = num2 != 0 ? num1 / num2 : 0; break;  // Avoid division by zero
        }
        lcd.clear();
        lcd.setCursor(0, 0);
        lcd.print("Result: ");
        lcd.print(result);
        delay(3000);
        input = "";
        lcd.clear();
      }
    } 
    else if (key == '*') {  // Clear key
      input = "";
      operation = 0;
      lcd.clear();
    }
  }
}