You see to want all integers so turning them from integers to strings and back again looks logical...
Then you can use +1 to increment the integers...
BUT if you wanted 'combined references' you can use say:
data = "A01"
Then later increment the string thus:
data.next!
which gives "A02"
The Ruby method .next increments strings, so x="A"; x.next!; x; "B" etc... .next returns the string incremented but leaves the original reference unchanged, adding the ! as in .next! also increments the reference itself.