Trial and error in C/C++

nfc-scanner.ino

/*
 * MFRC522 - Library to use ARDUINO RFID MODULE KIT 13.56 MHZ WITH TAGS SPI W AND R BY COOQROBOT.
 * The library file MFRC522.h has a wealth of useful info. Please read it.
 * The functions are documented in MFRC522.cpp.
 *
 * Based on code Dr.Leong   ( WWW.B2CQSHOP.COM )
 * Created by Miguel Balboa (circuitito.com), Jan, 2012.
 * Rewritten by Søren Thing Andersen (access.thing.dk), fall of 2013 (Translation to English, refactored, comments, anti collision, cascade levels.)
 * Released into the public domain.
 *
 * Sample program showing how to read data from a PICC using a MFRC522 reader on the Arduino SPI interface.
 *----------------------------------------------------------------------------- empty_skull
 * Aggiunti pin per arduino Mega
 * add pin configuration for arduino mega
 * http://mac86project.altervista.org/
 ----------------------------------------------------------------------------- Nicola Coppola
 * Pin layout should be as follows:
 * Signal     Pin              Pin               Pin			Pin
 *            Arduino Uno      Arduino Mega      SPARK			MFRC522 board
 * ---------------------------------------------------------------------------
 * Reset      9                5                 ANY (D2)		RST
 * SPI SS     10               53                ANY (A2)		SDA
 * SPI MOSI   11               51                A5				MOSI
 * SPI MISO   12               50                A4				MISO
 * SPI SCK    13               52                A3				SCK
 *
 * The reader can be found on eBay for around 5 dollars. Search for "mf-rc522" on ebay.com.
 */

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

#define SS_PIN SS
#define RST_PIN D2

char *lastCardID;
char *newCardID;

MFRC522 mfrc522(SS_PIN, RST_PIN);	// Create MFRC522 instance.

void setup() {
	Serial.begin(9600);	// Initialize serial communications with the PC

	mfrc522.setSPIConfig();

	mfrc522.PCD_Init();	// Init MFRC522 card
	Serial.println("Scan PICC to see UID and type...");
}

void loop() {
	// Look for new cards
	if ( ! mfrc522.PICC_IsNewCardPresent()) {
		return;
	}

	// Select one of the cards
	if ( ! mfrc522.PICC_ReadCardSerial()) {
		return;
	}

	// Dump debug info about the card. PICC_HaltA() is automatically called.
	//mfrc522.PICC_DumpToSerial(&(mfrc522.uid));

	// Dump UID
	Serial.print("Card UID:");
	newCardID = "";
	for (byte i = 0; i < mfrc522.uid.size; i++) {
		//Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
		//Serial.print(mfrc522.uid.uidByte[i], HEX);
		newCardID += mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ";
		newCardID += mfrc522.uid.uidByte[i], HEX;
		Serial.printf("%s", newCardID);
	}
	/*
	if (lastCardID != newCardID) {
		lastCardID = newCardID;
		Serial.print(newCardID);
	}
	*/
	Serial.println();
}