don't std::cout << sum the result but instead use return sum; opposed to your return 0;
That's why you'll always get 'Actual: 0' because your functionw ill always return 0 in any case.

Hey there. First things first, this should be marked as a question, not an issue. Issues are for when you think there is something wrong with the problem itself.

To answer your first question, usually you will work with what is given to you in the solution window. Changing what is already there can sometimes break a problem.

If you would like me to take a look at what you currently have, reply with your solution. I won't be able to help you further until then.