#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 20, 4);

#define ENCODER_CLK 2
#define ENCODER_DT   3
#define ENCODER_SW  4

int counter = 0;

void setup() {
  //  Initialize LCD
  lcd.init();
  lcd.backlight();

  //  Initialize encoder pins
  pinMode (ENCODER_CLK, INPUT);
  pinMode(ENCODER_DT, INPUT);
  pinMode (ENCODER_SW, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt (ENCODER_CLK), readEncoder, FALLING);
}

void readEncoder() {
  int dtValue =  digitalRead(ENCODER_DT);
  if (dtValue == HIGH) {
    counter++; // Clockwise
  }
  if (dtValue == LOW) {
    counter--; // Counterclockwise
  }
}

// Get the counter value, disabling interrupts.
// This make sure readEncoder() doesn't change the value
// while we're reading it.
int getCounter() {
  int result;
  noInterrupts();
  result = counter;
  interrupts();
  return result;
}

void resetCounter() {
  noInterrupts();
  counter = 0;
  interrupts();
}

void loop() {
  lcd.setCursor(3, 0);
  lcd.print("Counter:");
  lcd.setCursor(7, 1);
  lcd.print(getCounter());
  lcd.print("               ");

if (digitalRead(ENCODER_SW) == LOW) {
  resetCounter();
  }
}