0 
 for (byte i = 0; i < mfrc522.uid.size; i++)
  {
    Serial.print(mfrc522.uid.uidByte{i} < 0x10 ? " 0" : " ");
    Serial.print(mfrc522.uid.uidByte{i}, HEX);
    content.concat(String(mfrc522.uid.uidByte{i} < 0x10 ? " 0" : " "));
    content.concat(String(mfrc522.uid.uidByte{i}, HEX));
  }

I use this code to get UID of an RFID card, but the error "expected ')' before '{' token" comes out. Does anybody know how to solve this problem?

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  • 2
    This is a simple C(++) error and not Arduino-specific. To address array elements you should use square brackets ([, ]) instead of curly brackets. Replace all instances of {i} with [i] and you will be good to go.
    – StarCat
    Nov 23, 2020 at 9:31
  • 3
    I’m voting to close this question because it's a trivial syntax error question.
    – ocrdu
    Nov 23, 2020 at 12:52

1 Answer 1

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Welcome to this site, next time use ctrl-k to align your code.

The problem is in:

Serial.print(mfrc522.uid.uidByte{i} < 0x10 ? " 0" : " ");

To get the value of an array, use [i], not {i}, thus

Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");

(similar to other lines).

To give some additional hints:

  • Try to prevent duplicated code by storing the byte into a variable. Now you can use uidValue in the subsequent lines.

    uint8_t uidValue = mfrc522.uid.uidByte[i];

  • Store 0x10 inside a constant.

So you get:

const uint8_t MAX_HEX_SINGLE_DIGIT_VALUE 0x0F;

for (byte i = 0; i < mfrc522.uid.size; i++)
{
    uint8_t uid_byte = mfrc522.uid.uidByte[i];
    Serial.print(uid_byte < LOW_VALUE <= MAX_HEX_SINGLE_DIGIT_VALUE ? " 0" : " ");
    Serial.print(uid_byte, HEX);
    content.concat(String(uid_byte < MAX_HEX_SINGLE_DIGIT_VALUE ? " 0" : " "));
    content.concat(String((uid_byte, HEX));
  }

I assume the Serial lines are only for debugging, otherwise you can combine them too.

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  • 1
    Thank you very much, Michel.
    – Tingkai Yan
    Nov 23, 2020 at 9:32
  • 3
    Michel, if you answer a syntax error question, then at least without syntax errors. I thought you agreed that syntax error questions shouldn't be answered.
    – Juraj ♦
    Nov 23, 2020 at 12:26
  • 2
    they will reject a syntax error question. it is off-topic on SO
    – Juraj ♦
    Nov 23, 2020 at 12:31
  • 1
    to ask a question for every syntax error is not a way to learn codding. a codding course is a much better way
    – Juraj ♦
    Nov 23, 2020 at 17:57
  • 1
    @Juraj .. However, at least instead of answering a duplicate question could be found. Although I hope if the OP stays interested he will do a course, or at least find out how C(++) syntax works.
    – Michel Keijzers
    Nov 23, 2020 at 21:05

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