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

// Initialize the LCD with the address of the I2C chip
LiquidCrystal_I2C lcd(0x27, 16, 2);

// Define the keypad
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}; // Connect to the row pinouts of the keypad
byte colPins[COLS] = {5, 4, 3, 2}; // Connect to the column pinouts of the keypad

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

String input = ""; // String to store user input
float num1 = 0;
float num2 = 0;
char op;

void setup() {
  // Initialize the LCD
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0,0);
  lcd.print("Calculator:");
}

void loop() {
  char key = keypad.getKey(); // Read the keypad
  
  if (key) { // If a key is pressed
    if (key == 'C') { // Clear input
      input = "";
    } else if (key == '=') { // Calculate result
      lcd.clear();
      lcd.setCursor(0,0);
      lcd.print(input);
      lcd.setCursor(0,1);
      lcd.print("=");
      calculateResult();
      delay(2000);
      lcd.clear();
      lcd.setCursor(0,0);
      lcd.print("Calculator:");
    } else { // Append pressed key to input
      input += key;
    }
    lcd.setCursor(0,1);
    lcd.print(input);
  }
}

void calculateResult() {
  int pos = input.indexOfAny("+-*/"); // Find operator position
  if (pos != -1) {
    num1 = input.substring(0, pos).toFloat(); // Extract first number
    op = input[pos]; // Extract operator
    num2 = input.substring(pos + 1).toFloat(); // Extract second number
    float result = 0;
    switch(op) {
      case '+':
        result = num1 + num2;
        break;
      case '-':
        result = num1 - num2;
        break;
      case '*':
        result = num1 * num2;
        break;
      case '/':
        if (num2 != 0) {
          result = num1 / num2;
        } else {
          lcd.setCursor(0,1);
          lcd.print("Error: Div by 0");
          return;
        }
        break;
    }
    lcd.setCursor(0,1);
    lcd.print(result);
  }
}