Reading values from an array - arrays

Question

I am trying to read an RFID tag and compare the RFID number with a array which I have already there. In my code, the comparing is not working properly. It always gives output as both 'Found' and 'Not found'. Can any one help me on this?
The two RFID numbers that I want to read are: 37376B34 and 7AA29B1A. These two are only for testing. I'm going to store about 20 RFID numbers in the array and check.
My code:
#include <SPI.h>
#include <MFRC522.h>
#define SS_PIN 10
#define RST_PIN 9
MFRC522 mfrc522(SS_PIN, RST_PIN); // Create MFRC522 instance.
int readsuccess;
byte readcard[4];
char str[32] = "";
String StrUID;
char* myTags[] = {"9FF4375C","37376B34","7AA29B1A","1B7D5223","9FF4375C"};
void setup() {
Serial.begin(9600); // Initialize serial communications with the PC
SPI.begin(); // Init SPI bus
mfrc522.PCD_Init(); // Init MFRC522 card
}
// --------------------------------------------------------------------
void loop() {
readsuccess = getid();
if (readsuccess) {
Serial.println(StrUID);
delay(1000);
}
for (int i = 0; i < 5; i++) {
if (StrUID == myTags[i]) {
Serial.println("Found");
return;
} else {
Serial.println("Not Found");
}
}
}
// --------------------------------------------------------------------
int getid() {
if (!mfrc522.PICC_IsNewCardPresent()) {
return 0;
}
if (!mfrc522.PICC_ReadCardSerial()) {
return 0;
}
for (int i=0; i<4; i++) {
readcard[i] = mfrc522.uid.uidByte[i]; //storing the UID of the tag in readcard
array_to_string(readcard, 4, str);
StrUID = str;
}
mfrc522.PICC_HaltA();
return 1;
}
// --------------------------------------------------------------------
void array_to_string(byte array[], unsigned int len, char buffer[]) {
for (unsigned int i = 0; i < len; i++) {
byte nib1 = (array[i] >> 4) & 0x0F;
byte nib2 = (array[i] >> 0) & 0x0F;
buffer[i * 2 + 0] = nib1 < 0xA ? '0' + nib1 : 'A' + nib1 - 0xA;
buffer[i * 2 + 1] = nib2 < 0xA ? '0' + nib2 : 'A' + nib2 - 0xA;
}
buffer[len * 2] = '\0';
}

Answer 1

Data type byte in Arduino is just unsigned char in c++. Since the data that you read from the reader are in bytes, so it is possible to directly compare it with myTags without the need of using String object or even the array to string conversion. You can do the comparison with C++ memcmp() function.
const char* myTags[] = {"9FF4375C","37376B34","7AA29B1A","1B7D5223","9FF4375C"};
byte myReading[4] = {0x9f,0xf4,0x37,0x5c};
for (int i = 0; i < 5; i++) {
if (memcmp(myTags[i], myReading, sizeof(myReading)) == 0) {
Serial.println("Found");
return;
} else {
Serial.println("Not Found");
}
}