Arduino expected ')' before '{' token

Question

 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?

• StarCat: 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.
• ocrdu: I’m voting to close this question because it's a trivial syntax error question.

Answer 1

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.

• Tingkai Yan: Thank you very much, Michel.
• Juraj: 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: they will reject a syntax error question. it is off-topic on SO
• Juraj: to ask a question for every syntax error is not a way to learn codding. a codding course is a much better way
• Michel Keijzers: @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.