Grumpy_Mike:
In this case if you remove that iteration loop you do not need the variable reader at all, so it shouldn’t be in the code.
When you say the iteration loop, are you meaning the 'for' loop, and by 'you do not need the variable reader at all' you mean, maybe i should have declared this at the start, because anything that has reader in i.e (mfrc522[reader].PICC_ReadCardSerial()) wants reader to be understood, and without it, i get errors too.