Arduino RFID

#include <SPI.h>
#include <MFRC522.h>

constexpr uint8_t RST_PIN = 9;
constexpr uint8_t SS_PIN = 10;
int ledPin = 7;
MFRC522 mfrc522(SS_PIN, RST_PIN);

void setup() {
    Serial.begin(9600);
    while (!Serial);
    SPI.begin();
  pinMode(ledPin, OUTPUT);
}

void loop() {
    if ( ! mfrc522.PICC_IsNewCardPresent()) {
        return;
    }
    if ( ! mfrc522.PICC_ReadCardSerial()) {
        return;
    }

  digitalWrite(ledPin, HIGH);
  long code=0;
  for (byte i = 0; i < mfrc522.uid.size; i++)
  {
  code=((code+mfrc522.uid.uidByte[i])*10);
  }
   Serial.println(code);
   delay (2000);
   digitalWrite(ledPin, LOW);
}