Well, my point is that the code he really wants to start with, to which I linked, does not appear to use "String"s so it would appear they are entirely unnecessary in the first place. 
I am trying to make it simple. That code provides all the functionality of easily adding and removing multiple tags/ cards as well as the basic validation of the correct card. It has some extra stuff to operate a servo as the actuator which can be adapted as required. 