Calculator_Sunil_Singh_Serial_Monitor

#include <Keypad.h>

#include <Wire.h>

#include <LiquidCrystal_I2C.h>

// Keypad configuration

const byte ROWS = 4, COLS = 4;

char keys[ROWS][COLS] = {

  {'1','2','3','+'},

  {'4','5','6','-'},

  {'7','8','9','*'},

  {'C','0','=','/'}

};

byte rowPins[ROWS] = {9,8,7,6};

byte colPins[COLS] = {5,4,3,2};

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

// LCD configuration

LiquidCrystal_I2C lcd(0x27, 16, 2);

// Calculator variables

String input = "";

float num1 = 0, num2 = 0;

char operatorSymbol = ' ';

bool resultShown = false;

bool enteringSecondOperand = false;

void setup() {

  Serial.begin(9600);

  lcd.init();

  lcd.backlight();

  lcd.setCursor(0, 0);

  lcd.print("Calculator");

  delay(1000);

  lcd.clear();

  Serial.println("Setup complete — ready.");

}

void loop() {

  char key = keypad.getKey();

  if (key != NO_KEY) {

    Serial.print("Key pressed: ");

    Serial.println(key);

    if (resultShown) {

      lcd.clear();

      resultShown = false;

      Serial.println("LCD cleared (after showing result).");

    }

    if (isdigit(key) || key == '.') {

      input += key;

      Serial.print("Building number: ");

      Serial.println(input);

      if (enteringSecondOperand) {

        lcd.setCursor(String(num1).length() + 1 + input.length() - 1, 0);

      } else {

        lcd.setCursor(input.length() - 1, 0);

      }

      lcd.print(key);

    }

    else if (key == '+' || key == '-' || key == '*' || key == '/') {

      num1 = input.toFloat();

      operatorSymbol = key;

      input = "";

      enteringSecondOperand = true;

      lcd.setCursor(String(num1).length(), 0);

      lcd.print(operatorSymbol);

      Serial.print("First operand: ");

      Serial.println(num1);

      Serial.print("Operator: ");

      Serial.println(operatorSymbol);

    }

    else if (key == '=') {

      num2 = input.toFloat();

      input = "";

      enteringSecondOperand = false;

      Serial.print("Second operand: ");

      Serial.println(num2);

      float result = 0;

      switch (operatorSymbol) {

        case '+': result = num1 + num2; break;

        case '-': result = num1 - num2; break;

        case '*': result = num1 * num2; break;

        case '/': result = num1 / num2; break;

        default:

          lcd.setCursor(0, 1);

          lcd.print("Error");

          delay(1000);

          lcd.clear();

          Serial.println("Error: invalid operator.");

          return;

      }

      lcd.setCursor(0, 1);

      lcd.print("Result: ");

      lcd.print(result);

      resultShown = true;

      Serial.print("Result displayed: ");

      Serial.println(result);

    }

    else if (key == 'C') {

      input = "";

      num1 = num2 = 0;

      operatorSymbol = ' ';

      enteringSecondOperand = false;

      resultShown = false;

      lcd.clear();

      Serial.println("Cleared all inputs.");

    }

  }

}