#include <LiquidCrystal_I2C.h> 
#define BTN_A 5
#define BTN_B 3
#define BTN_ACTION 4
#define BTN_CALC 2

LiquidCrystal_I2C lcd(0x27,16,2);

int a = 0;
int b = 0;
int action = 0;
int result = 0;

void setup() {
  lcd.init();
  lcd.clear();        
  lcd.backlight();
  pinMode(BTN_A, INPUT_PULLUP);
  pinMode(BTN_B, INPUT_PULLUP);
  pinMode(BTN_ACTION, INPUT_PULLUP);
  pinMode(BTN_CALC, INPUT_PULLUP);
}

void loop() {
  if(digitalRead(BTN_A)==LOW){
    delay(200); 
    a = a + 1; 
  }

  if(digitalRead(BTN_B)==LOW){
    delay(200); 
    b = b + 1; 
  }

  if(digitalRead(BTN_ACTION)==LOW){
    delay(500); 
    action = action + 1;
    if (action > 3){
      action = 0;
    }
  }

  if(digitalRead(BTN_CALC)==LOW){
    delay(500); 
    lcd.setCursor(0,0);
    if (action == 0){
      result = a + b; 
      lcd.print(String(a) + " + " + String(b) + " = " + String(result));
    }
    if (action == 1){
      result = a - b; 
      lcd.print(String(a) + " - " + String(b) + " = " + String(result));
    }

    if (action == 2){
      result = a * b; 
      lcd.print(String(a) + " * " + String(b) + " = " + String(result));
    }

    if (action == 3){
      if(b > 0){
        result = a / b; 
        lcd.print(String(a) + " / " + String(b) + " = " + String(result));
      } else {
        lcd.print("Error divide 0");
      }
    }
  }

  lcd.setCursor(0,0);
  if (action == 0){
    lcd.print(String(a) + " + " + String(b));
  }
  if (action == 1){
    lcd.print(String(a) + " - " + String(b));
  }
  if (action == 2){
    lcd.print(String(a) + " * " + String(b));
  }
  if (action == 3){
    lcd.print(String(a) + " / " + String(b));
  }

}