//calculator program
#include <LiquidCrystal.h>
#include <Keypad.h>

LiquidCrystal lcd(13, 12, 11, 10, 9, 8);

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] = {7, 6, 5, 4}; // Rows 0 to 3
byte colPins[COLS] = {3, 2, 1, 0}; // Columns 0 to 3

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

int operand1 = 0;
int operand2 = 0;
char operation;
bool calculating = false;

void setup() {
  lcd.begin(16, 2);
  lcd.print("Calculator:");
}

void loop() {
  char key = keypad.getKey();
  
  if (key != NO_KEY) {
    if (key == 'C') {
      clearCalculator();
    } else if (key >= '0' && key <= '9') {
      if (!calculating) {
        operand1 = operand1 * 10 + (key - '0');
        lcd.setCursor(0, 1);
        lcd.print(operand1);
      } else {
        operand2 = operand2 * 10 + (key - '0');
        lcd.setCursor(8, 1);
        lcd.print(operand2);
      }
    } else if (key == '+' || key == '-' || key == '*' || key == '/') {
      operation = key;
      lcd.setCursor(7, 1);
      lcd.print(operation);
      calculating = true;
    } else if (key == '=') {
      float result = 0;
      switch(operation) {
        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: Div by 0");
            delay(2000);
            clearCalculator();
            break;
          }
          break;
      }
      lcd.setCursor(0, 1);
      lcd.clear();
      lcd.print(result);
      delay(5000);
      clearCalculator();
    }
  }
}

void clearCalculator() {
  operand1 = 0;
  operand2 = 0;
  operation = ' ';
  calculating = false;
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Calculator:");
}