This code checks 10 and 11 digital pins of rotary encoder and add or subtract from counter variable.

Encoder checking Arduino

int counter = 0;
bool R, L, END, ROT;
bool A, B;
bool ff, tf, ft, tt;
bool mode = true;

void setup() {
	pinMode(10, INPUT_PULLUP);
	pinMode(11, INPUT_PULLUP);
}

void loop() {
	A = digitalRead(10);
	B = digitalRead(11);

	ff = !A && !B;
	tf = A && !B;
	ft = !A && B;
	tt = A && B;
  
	if(ft && !(END || R || L)) R = true;
	if(tf && !(END || R || L)) L = true;

	if(ff && (R || L)) R = L = END = false;

	if(tf && R) {
		R = false;
		END = ROT = true;
	}
	if(ft && L) {
		L = ROT = false;
		END = true;
	}

	if(tt && END) R = L = END = false;
	if(ff && END) {
		END = false;
		if(ROT) counter += 1;
		else counter -= 1;
	}
}