Trailer cards describes the reserved variable
thisread, which keeps track of which cards have been read in during the current read, and
allread, which keeps track of all cards read in for the current record. Other reserved variables associated with reading in data:
Set to true when the last record in the file has been read or, in the case of trailer cards, the last read of the last record has occurred.
Stores the number of records read in so far.
Counts the number of cards read so far.