#include <LiquidCrystal.h>
int rs = 7;
int en = 8;
int d4 = 9;
int d5 = 10;
int d6 = 11;
int d7 = 12;

float firstNum;
float secondNum;
float answer;

LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

String op;

void setup() {
  // put your setup code here, to run once:
  lcd.begin(16, 2);
  Serial.begin(9600);
}

void loop() {
  lcd.setCursor(0, 0);
  lcd.print("Input 1st number");
  Serial.println("Write here: ");
  while(Serial.available() == 0){}
  firstNum = Serial.parseFloat();
  lcd.clear();

  lcd.setCursor(0, 0);
  lcd.print("Input 2nd number");
  Serial.println("Write here: ");
  while(Serial.available() == 0){}
  secondNum = Serial.parseFloat();
  lcd.clear();

while(true){
    lcd.setCursor(0, 0);
    lcd.print("Input (+ - / *)");
    Serial.println("Write here: ");
    while(Serial.available() == 0){}
    op = Serial.readString();
    lcd.clear();

    if(op == "+"){
      answer = firstNum + secondNum;
      break;
    } else if(op == "-") {
      answer = firstNum - secondNum;
      break;
    } else if (op == "*"){
      answer = firstNum * secondNum;
      break;
    } else if(op == "/"){
      answer = firstNum / secondNum;
      break;
    } else {
      Serial.println("Input not recognised. Please try again.");
    } 
  }

  lcd.setCursor(0, 0);
  lcd.print(firstNum + op + secondNum + " = " + answer);
  lcd.setCursor(0, 1);
  lcd.print("Thank you");
  delay(5000);
  lcd.clear();
}