Storing and comparing byte values in C

Question

I have an Arduino Uno setup with a MFRC522 RFID Receiver module. I am attempting to create a verification system in which I use the UID of the card to turn on an LED Here is my current code:

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

#define SS_PIN 10
#define RST_PIN 9
MFRC522 mfrc522(SS_PIN, RST_PIN);   // Create MFRC522 instance.

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

    byte readCard[7] ;
    byte cardCode[7] = E05E987;

Serial.println("Scanned PICC's UID:");
for (int i = 0; i < mfrc522.uid.size; i++) {
    readCard[i] = mfrc522.uid.uidByte[i];
    Serial.print(readCard[i], HEX);
  }
  Serial.println("");


  if (readCard == cardCode){
    Serial.println("Correct Code");
    return;
    }
}

However, When I compile this code I am met with this error:

/root/Arduino/RFID_Check_/RFID_Check_.ino: In function 'void loop()':
RFID_Check_:28: error: 'E05E987' was not declared in this scope
     byte cardCode[7] = E05E987;
                        ^
exit status 1
'E05E987' was not declared in this scope

How can resolve this error? I have tried changing the values inbetween he square brackets to no avail.

Answer 1

You decare an array of 7 bytes. It seems you want to assign it a value; however, the value isn't appropriate for a byte.

To assign a hexadecimal value, you must precede it with 0x so 0xE05E987 would be a proper hexadecimal value.

But that value is too large for a byte. You can assign the values to the array as follows:

byte cardCode[7] = {0xE0, 0x5E, 0x98, 0x07};

Any value not provided will be zero. The above has initialized cardCode[0] through cardCode[3] and has set the remainder to zero.