#include <Keypad.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

const byte ROWS = 4; 
const byte COLS = 4; 

char hexaKeys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};

byte rowPins[ROWS] = {9, 8, 7, 6}; 
byte colPins[COLS] = {5, 4, 3, 2}; 
Keypad customKeypad = Keypad(makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS);
LiquidCrystal_I2C lcd(0x27, 16, 2);

int num1;
int num2;
char ch;
String wrt = "";
bool wrtres = true;
bool input = true;
bool num1i = false;
bool num2i = false;
bool chi = false;
int res;
char currmode;

void setup() {
  Serial.begin(9600);
  lcd.init();
  lcd.backlight();
}

void loop() {
  char keypad = customKeypad.getKey();
  lcd.setCursor(1, 0);
  lcd.print(num1);
  lcd.print("    ");
  lcd.setCursor(6, 0);
  lcd.print(ch);
  lcd.print("    ");
  lcd.setCursor(12, 0);
  lcd.print(num2);
  lcd.print("    ");
  lcd.setCursor(2, 1);
  lcd.print("= ");
  lcd.print(res);
  lcd.print("           ");
  if(keypad){
    if(!num1i && !num2i && !chi){
      if(keypad >= '0' && keypad <= '9'){
        wrt += keypad;
        num1 = wrt.toInt();
      }
      else{
        switch(keypad){
          case 'A':
            ch = '+';
            chi = true;
            num1i = true;
            wrt = "";
            break;
          case 'B':
            ch = '-';
            chi = true;
            num1i = true;
            wrt = "";
            break;
          case 'C':
            ch = '*';
            chi = true;
            num1i = true;
            wrt = "";
            break;
          case 'D':
            ch = '/';
            chi = true;
            num1i = true;
            wrt = "";
            break;
        }
      }
    }
    else if(num1 && chi && !num2i){
      if(keypad >= '0' && keypad <= '9'){
        wrt += keypad;
        num2 = wrt.toInt();
      }
      else{
        switch(keypad){
          case '#':
            switch(ch){
              case '+':
                res = num1 + num2;
                num2i = true;
                wrt = "";
                break;
              case '-':
                res = num1 - num2;
                num2i = true;
                wrt = "";
                break;
              case '*':
                res = num1 * num2;
                num2i = true;
                wrt = "";
                break;
              case '/':
                res = num1 / num2;
                num2i = true;
                wrt = "";
                break;
            }
            break;

        }

      }
    }
    switch(keypad){
      case '*':
        num2i = false;
        num1i = false;
        chi = false;
        num1 = 0;
        num2 = 0;
        ch = ' ';
        res = 0;
        break;
    }
  }
  Serial.println(keypad);
}