#define SET1(r,b) r|=1<<b
#define SET0(r,b) r&=~(1<<b)
#define TEST(r,b) (r&(1<<b))

#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16,2);

int num = 0;
bool activeLCD;
bool vosiel;
bool vosiel1;

void setup(){
  Serial.begin(9600);
  
  lcd.init();
  lcd.backlight();
  
  SET1(PORTB, 0);
  SET1(PORTB, 1);
  
  SET1(PCMSK0, PCINT0);
  SET1(PCMSK0, PCINT1);
  
  SET1(PCICR, PCIE0);
  SET1(SREG, 7);
  
  vosiel = TEST(PINB, 0);
  vosiel1 = TEST(PINB, 1);
  
  lcd.print("Zadaj cislo!");
}

void loop(){
  if(Serial.available()){
    //String pismeno = Serial.readStringUntil('+');
    num = Serial.parseInt();
    Serial.println("Zadal si: "+String(num));
    lcd.clear();
    lcd.print(num);
  }
  
  if(activeLCD == true){
    activeLCD = false;
  	lcd.clear();
    lcd.print(num);
  }
  
  vosiel = TEST(PINB, 0);
  vosiel1 = TEST(PINB, 1);
}

ISR(PCINT0_vect){
  if(TEST(PINB, 0) == 0 && vosiel != 0){
  	num++;
    activeLCD = true;
  }
    
  if(TEST(PINB, 1) == 0 && vosiel1 != 0){
  	num--;
    activeLCD = true;
  }
}