Trying to access the next character with &c might give you a bad memory address because it's getting the address of the reference variable c and not necessarily the next character in the string.

You are right. I probably thought that one of the variables could have been 0, but the description mentions that the given numbers are in the range from 1 to 10.

Its great math but a bad 8 kyu question. In my opinion 8 kyu questions should be aimed to 10 year old kids with a Programming book at hand.

This gives the line "she made a mistake" a whole other meaning. Good Job.