#include<Keypad.h>
#include<LiquidCrystal_I2C.h>
const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
  {'1', '2', '3', '+'},
  {'4', '5', '6', '-'},
  {'7', '8', '9', '.'},
  {'*', '0', '=', '/'}
};

byte rowPins[ROWS] = {9, 8, 7, 6};
byte colPins[COLS] = {5, 4, 3, 2};
Keypad myKeypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);
LiquidCrystal_I2C lcd(0x27, 20, 4);
int sw = 10;
boolean num1State = true;
String num1 = "";
String num2 = "";
float result ;
char op = ' ';

void setup() {
  pinMode(sw, INPUT_PULLUP);
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("ALI Calculator");
  delay(1000);
  Serial.begin(9600);
  clr();
}

void loop() {
  char Key = myKeypad.getKey();
  if (Key != NO_KEY && (Key == '.' || Key == '1' || Key == '2' || Key == '3' || Key == '4' || Key == '5' || Key == '6' || Key == '7' || Key == '8' || Key == '9' || Key == '0')) {

    if (num1State == true) {
      num1 += Key; //num2 =num + Key;

      lcd.print(Key);
    }
    else {
      num2 += Key;//num2 =num + Key;

      lcd.print(Key);
    }
  }
  if (Key != NO_KEY && (Key == '+' || Key == '-' || Key == '*' || Key == '/')) {
    if (num1State == true) {
      op = Key;
      num1State = false;
      lcd.setCursor(0, 1);
      lcd.print(op);
      lcd.setCursor(0, 2);
    }
  }
  if (Key != NO_KEY && Key == '=') {
    if (op == '+') {
      result = num1.toFloat() + num2.toFloat();
    }

    if (op == '-') {
      result = num1.toFloat() - num2.toFloat();
    }

    if (op == '*') {
      result = num1.toFloat() * num2.toFloat();
    }

    if (op == '/') {
      result = num1.toFloat() / num2.toFloat();
    }
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print(num1);
    lcd.print(op);
    lcd.print(num2);
    lcd.setCursor(0, 1);
    lcd.print("=");
    lcd.setCursor(0, 2);
    lcd.print(result);
    num1State = true;
  }
  int val = digitalRead(sw);
  delay(100);
  if (val == 1) {
    clr();
  }
}
void clr() {
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("");
  lcd.setCursor(0, 1);
  lcd.print("");
  lcd.setCursor(0, 2);
  lcd.print("");
  lcd.setCursor(0, 0);
  num1 = "";
  num2 = "";
  result = 0;
  op = ' ';
}