Now, I did that as an exercise, see if I could figure out the parsing and all of that. Great. However, what I need are INTs, not Strings.
A couple corrections. What you need are ints, not strings. Ditch the String class. You will run out of memory that way.
A fixed array of chars that you store c in (and increment an index and add a NULL terminator to) will, overall, use less memory. Each time you encounter a comma, call atoi() to convert the value to an int, and reset index (and put a NULL in the 0th position of the array).