Arduino interfacing with Calculator

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

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};
byte colPins[COLS] = {3, 2, A2, A3};

// Created instances
Keypad myKeypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);
LiquidCrystal lcd(13, 12, 11, 10, 9, 8); // Initialize the LCD on these pins

boolean firstNumState = true;
String firstNum = "";
String secondNum = "";
float result = 0.0;
char operatr = ' ';

const int squareButtonPin = A0; // Connect 'Square' button to analog pin A0
const int cubeButtonPin = A1;  // Connect 'Cube' button to analog pin A1

void setup() {
  lcd.begin(16, 2);
  lcd.setCursor(0, 0);
  lcd.print("Arduino Calculator");
  lcd.setCursor(0, 1);
  lcd.print("by Your Name");
  delay(1000);
  lcd.clear();
  clr();

  pinMode(squareButtonPin, INPUT_PULLUP);
  pinMode(cubeButtonPin, INPUT_PULLUP);
}

void loop() {
  char newKey = myKeypad.getKey();

  if (newKey != NO_KEY && (newKey == '1' || newKey == '2' || newKey == '3' || newKey == '4' || newKey == '5' || newKey == '6' || newKey == '7' || newKey == '8' || newKey == '9' || newKey == '0')) {

    if (firstNumState == true) {
      firstNum = firstNum + newKey;
      lcd.print(newKey);
    }
    else {
      secondNum = secondNum + newKey;
      lcd.print(newKey);
    }
  }

  if (newKey != NO_KEY && (newKey == '+' || newKey == '-' || newKey == '*' || newKey == '/')) {
    if (firstNumState == true) {
      operatr = newKey;
      firstNumState = false;
      lcd.setCursor(15, 0);
      lcd.print(operatr);
      lcd.setCursor(5, 1);
    }
  }

  if (newKey != NO_KEY && newKey == '=') {
    if (operatr == '+') {
      result = firstNum.toFloat() + secondNum.toFloat();
    }

    if (operatr == '-') {
      result = firstNum.toFloat() - secondNum.toFloat();
    }

    if (operatr == '*') {
      result = firstNum.toFloat() * secondNum.toFloat();
    }

    if (operatr == '/') {
      result = firstNum.toFloat() / secondNum.toFloat();
    }

    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print(firstNum);
    lcd.print(operatr);
    lcd.print(secondNum);
    lcd.setCursor(0, 1);
    lcd.print("=");
    lcd.print(result);
    firstNumState = true;
  }

  if (newKey != NO_KEY && newKey == 'C') {
    clr();
  }

  if (digitalRead(squareButtonPin) == LOW) {
    // 'Square' button is pressed
    float num = firstNum.toFloat();
    float square = num * num;
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Square of ");
    lcd.print(num);
    lcd.setCursor(0, 1);
    lcd.print("is");
    lcd.setCursor(5, 1);
    lcd.print(square);
    delay(2000);
    clr();
  }

  if (digitalRead(cubeButtonPin) == LOW) {
    // 'Cube' button is pressed
    float num = firstNum.toFloat();
    float cube = num * num * num;
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Cube of ");
    lcd.print(num);
    lcd.setCursor(0, 1);
    lcd.print("is");
    lcd.setCursor(5, 1);
    lcd.print(cube);
    delay(2000);
    clr();
  }
}

void clr() {
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("1st: ");
  lcd.setCursor(12, 0);
  lcd.print("op ");
  lcd.setCursor(0, 1);
  lcd.print("2nd: ");
  lcd.setCursor(5, 0);
  firstNum = "";
  secondNum = "";
  result = 0;
  operatr = ' ';
}