Void as an int?

Using Arduino Programming Questions
1

This void prints the rfid value on the lcd screen;

void dump_byte_array(byte *buffer, byte bufferSize) {   
        for (byte x=0; x < bufferSize; x++){
        lcd.print(buffer[x] < 16 ? "0" :""); //value cannot be bigger than 16 digits
          lcd.print(buffer[x], HEX);
    }
       }

When you include the void in the loop();
dump_byte_array(mfrc522.uid.uidByte, mfrc522.uid.size);
its like that, but I wanna store the value it gives out as a int. So I can make name tags for each rfid card. ex;

 if(valueoncard=="81949B75"){ 
    
    lcd.print("Name1");
    
  }else if(valueoncard=="839FA9D5"){ 
    
    lcd.print("Name2");
    
  }else if(dvalueoncard=="938C8F00"){ 
    
    lcd.print("Name3");
    
  }else if(valueoncard=="45E09F2C"){ 
    
    lcd.print("Name4");
    
  }else{
    
    lcd.print("Your card has not been entered into the database. Sorry frown emoticon");
  }

Hope this kinda makes sense. :confused:

Thanks for the help guys!

This is what everything looks like so far, we can make it print the value, but we want it to print out names.

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

LiquidCrystal lcd (7,6,5,4,3,2);

#define RST_PIN         9           // Configurable, see typical pin layout above
#define SS_PIN          10          // Configurable, see typical pin layout above
byte id;
MFRC522 mfrc522(SS_PIN, RST_PIN);   // Create MFRC522 instance.

// Number of known default keys (hard-coded)
// NOTE: Synchronize the NR_KNOWN_KEYS define with the defaultKeys[] array
#define NR_KNOWN_KEYS   8
// Known keys, see: https://code.google.com/p/mfcuk/wiki/MifareClassicDefaultKeys
byte knownKeys[NR_KNOWN_KEYS][MFRC522::MF_KEY_SIZE] =  {
    {0xff, 0xff, 0xff, 0xff, 0xff, 0xff}, // FF FF FF FF FF FF = factory default
    {0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5}, // A0 A1 A2 A3 A4 A5
    {0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5}, // B0 B1 B2 B3 B4 B5
    {0x4d, 0x3a, 0x99, 0xc3, 0x51, 0xdd}, // 4D 3A 99 C3 51 DD
    {0x1a, 0x98, 0x2c, 0x7e, 0x45, 0x9a}, // 1A 98 2C 7E 45 9A
    {0xd3, 0xf7, 0xd3, 0xf7, 0xd3, 0xf7}, // D3 F7 D3 F7 D3 F7
    {0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff}, // AA BB CC DD EE FF
    {0x00, 0x00, 0x00, 0x00, 0x00, 0x00}  // 00 00 00 00 00 00
};

/*
 * Initialize.
 */
void setup() {
  lcd.begin(16, 2);
    lcd.print("Scan a card");
    lcd.setCursor(0,2);
    Serial.begin(9600);         // Initialize serial communications with the PC
    while (!Serial);            // Do nothing if no serial port is opened (added for Arduinos based on ATMEGA32U4)
    SPI.begin();                // Init SPI bus
    mfrc522.PCD_Init();         // Init MFRC522 card
    Serial.println(F("Try the most used default keys to print block 0 of a MIFARE PICC."));
}

/*
 * Helper routine to dump a byte array as hex values to Serial.
 */
void dump_byte_array(byte *buffer, byte bufferSize) {   
 for (byte x=0; x < bufferSize; x++){
        lcd.print(buffer[x] < 16 ? "0" :"");
        lcd.print(buffer[x], HEX);
 }
}

void uids(){
  //You need to find a way to turn the value into an int
  //You've tried including the void and such.
  if(dump_byte_array(mfrc522.uid.uidByte, mfrc522.uid.size)=="81949B75"){ 
    
    lcd.print("Name1");
    
  }else if(dump_byte_array(mfrc522.uid.uidByte, mfrc522.uid.size)=="839FA9D5"){ 
    
    lcd.print("Name2");
    
  }else if(dump_byte_array(mfrc522.uid.uidByte, mfrc522.uid.size)=="938C8F00"){ 
    
    lcd.print("Name3");
    
  }else if(dump_byte_array(mfrc522.uid.uidByte, mfrc522.uid.size)=="45E09F2C"){ 
    
    lcd.print("Name4");
    
  }else{
    
    lcd.print("Your card has not been entered into the database. Sorry frown emoticon");
  }
  
}
*/
void dump_byte_array1(byte *buffer, byte bufferSize) {
    for (byte i = 0; i < bufferSize; i++) {
        //Serial.print(buffer[i] < 0x10 ? " 0" : " ");
        Serial.print(buffer[i] < 16 ? "0" : "");
        //Serial.print(buffer[i], HEX);
    }
}

/*
 * Try using the PICC (the tag/card) with the given key to access block 0.
 * On success, it will show the key details, and dump the block data on Serial.
 *
 * @return true when the given key worked, false otherwise.
 */
boolean try_key(MFRC522::MIFARE_Key *key)
{
    boolean result = false;
    byte buffer[18];
    byte block = 0;
    byte status;
    
    // Serial.println(F("Authenticating using key A..."));
    status = mfrc522.PCD_Authenticate(MFRC522::PICC_CMD_MF_AUTH_KEY_A, block, key, &(mfrc522.uid));
    if (status != MFRC522::STATUS_OK) {
        // Serial.print(F("PCD_Authenticate() failed: "));
        // Serial.println(mfrc522.GetStatusCodeName(status));
        return false;
    }

    // Read block
    byte byteCount = sizeof(buffer);
    status = mfrc522.MIFARE_Read(block, buffer, &byteCount);
    if (status != MFRC522::STATUS_OK) {
        // Serial.print(F("MIFARE_Read() failed: "));
        // Serial.println(mfrc522.GetStatusCodeName(status));
    }
    else {
        // Successful read
        result = true;
        dump_byte_array((*key).keyByte, MFRC522::MF_KEY_SIZE);
        Serial.println();
        // Dump block data
        Serial.print(F("Block ")); lcd.print(block); Serial.print(F(":"));
        dump_byte_array(buffer, 16);
        Serial.println();
    }
    Serial.println();

    mfrc522.PICC_HaltA();       // Halt PICC
    mfrc522.PCD_StopCrypto1();  // Stop encryption on PCD
    return result;
}

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

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

    // Show some details of the PICC (that is: the tag/card)
Serial.print(F("Card UID:"));
dump_byte_array1(mfrc522.uid.uidByte, mfrc522.uid.size);
    dump_byte_array(mfrc522.uid.uidByte, mfrc522.uid.size);
    delay(1000);
    lcd.clear();
    lcd.print("Scan a card");
    lcd.setCursor(0,2);
    //lcd.clear();
    Serial.println();
  
}
2

"void" is the return type of a function and means that nothing is returned to the program segment that calls the function.

"dump_byte_array(byte *buffer, byte bufferSize)" is a function, not a void.

3

Here's a hint. It's not called a void, it's called a function. The word void there means it returns nothing. IF instead of void it were to say int, then it could have a return statement and return an int.

Google "C++ functions" and you'll find several good tutorials.

4

I mean int as in, int led =2;.

5

Right, you want to be able to say,

int valueOnCard = dump_byte_array(mfrc522.uid.uidByte, mfrc522.uid.size);

The question is what number from that function do you want to store there. You can't return an array. If it is 2 bytes you can store it as an int, or 4 bytes in a long. What exactly are we storing here? Either way, the function would have to return something, so it can't say "void" in front of it. It would have to say the type of thing you intend to return from it.

6

The value will be 4 bytes. It will store something like 3F 22 B4 FF and it will check through the predefined stuff to check what it should print.

7

OK. If it's 4 bytes you can store it in a long.

Really, if you've got it in that byte array to send it to this function then you already have it.

But here it is if you want to return it from here.

unsigned long dump_byte_array(byte *buffer, byte bufferSize) {   
  for (byte x=0; x < bufferSize; x++){
    lcd.print(buffer[x] < 16 ? "0" :""); //value cannot be bigger than 16 digits
    lcd.print(buffer[x], HEX);
  }
  
  unsigned long retval = 0;
   // if your numbers come out backwards, change this to 
   //  for (int i = 3; i >= 0; i--) {
  for (int i = 0; i < 4; i++){
    retval = retval << 8;
    retval |= buffer[i];
  }
  return retval;  
}

then in your code you can get it as

unsigned long valueOnCard = dump_byte_array(mfrc522.uid.uidByte, mfrc522.uid.size);

and compare with

if(valueOnCard == 0x81949B75) {
     Serial.println(name1);
}