main.cpp

#include "Arduino.h"
#include "HardwareSerial.h"

#define outputA 6
#define outputB 7

const int pin = 13;

const int counter = 0; 
const int aState;
const int aLastState; 

 void setup() { 
   pinMode (outputA,INPUT);
   pinMode (outputB,INPUT);

   Serial.begin (9600);
   // Reads the initial state of the outputA
   aLastState = digitalRead(outputA);
 }

void loop() { 
  aState = digitalRead(outputA); // Reads the "current" state of the outputA
  // If the previous and the current state of the outputA are different, that means a Pulse has occured
  if (aState != aLastState){
    // If the outputB state is different to the outputA state, that means the encoder is rotating clockwise
    if (digitalRead(outputB) != aState) {
      counter ++;
    } else {
      counter --;
    }
    Serial.print("Position: ");
    Serial.println(counter);
  }
  aLastState = aState; // Updates the previous state of the outputA with the current state
}

int main(void)
{
	init();

	setup();

	for (;;) {
		loop();
	}

	return 0;
}