#include <Keypad.h>
#include <LiquidCrystal.h>

LiquidCrystal lcd(41, 53, 51, 49, 47, 45, 43);

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] = {52, 50, 48, 46}; // connect to the row pinouts of the keypad
byte colPins[COLS] = {44, 42, 40, 38}; // connect to the column pinouts of the keypad

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

String inputBuffer = ""; // buffer to store input
float operand1 = 0;
float operand2 = 0;
char operatorSymbol = '\0';

void setup() {
  pinMode(38, INPUT);
  pinMode(40, INPUT);
  pinMode(42, INPUT);
  pinMode(44, INPUT);
  pinMode(46, INPUT);
  pinMode(48, INPUT);
  pinMode(50, INPUT);
  pinMode(52, INPUT);

  pinMode(41, OUTPUT);
  pinMode(43, OUTPUT);
  pinMode(45, OUTPUT);
  pinMode(47, OUTPUT);
  pinMode(49, OUTPUT);
  pinMode(51, OUTPUT);
  pinMode(53, OUTPUT);

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

void loop() {
  char key = keypad.getKey();
  
  if (key != NO_KEY) {
    lcd.print(key);
    
    if (isdigit(key)) {
      // If it's a digit or '.', add it to the buffer
      inputBuffer += key;
    } else if (key == '+' || key == '-' || key == '*' || key == '/') {
      // If it's an operator, handle it accordingly
      if (inputBuffer != "") {
        operand1 = inputBuffer.toFloat();
        operatorSymbol = key;
        inputBuffer = "";
      }
    } else if (key == '=') {
      // If it's '=', handle the calculation
      if (inputBuffer != "") {
        operand2 = inputBuffer.toFloat();
        inputBuffer = "";
        float result;

        switch (operatorSymbol) {
          case '+':
            result = operand1 + operand2;
            break;
          case '-':
            result = operand1 - operand2;
            break;
          case '*':
            result = operand1 * operand2;
            break;
          case '/':
            if (operand2 != 0) {
              result = operand1 / operand2;
            } else {
              lcd.clear();
              lcd.print("Error: Division by zero");
              delay(2000);
              lcd.clear();
              return;
            }
            break;
          default:
            result = 0;
        }

        lcd.clear();
        lcd.print("Result: ");
        lcd.setCursor(0, 1);
        lcd.print(result);
        delay(2000);
        lcd.clear();
      }
    } else if (key == 'C') {
      // If it's 'C', clear the buffer and the display
      inputBuffer = "";
      operand1 = 0;
      operand2 = 0;
      operatorSymbol = '\0';
      lcd.clear();
    }
  }
}