Like tuxdev said, it is better to use 0,1,2,3.
Then what he says about base 4 being nice, he means that you can easily convert to a base 4 number representation.
Consider (for example) a 3-digit base 4 number:
In hex representation that is: 0x1B, bin: 01 1011
Add one to that number, using your normal '+' function: you get 0x1C (01 1100)
Convert that back to base 4:
Now because number are represented binary in your computer, the easiest way to convert hex to quaternary is:
digit = new_number & 0x3 //leaves only the rightmost bits
new_number = new_number shr 2 //move to the next digit
until nr_digits >= max_digits;
How to string all those digits together I leave happily to you. Above code is not syntactically correct but you get the idea.
Any chance to implement those DNA strings and create a dino?