I think it would be very helpful if you first polished this code with the following:

1. Comments - what is each section/loop doing, in exact words? Break it down for both yourself and the reader.
2. Fuller variable names - iterators like 'i' and 'j' are fine, but 'ct' and 'cWord' could be named to better communicate what their purposes are, e.g. 'count' and 'result'
3. Consistency - Don't use both one-line ifs and bracketed ifs! Ideally I like brackets everywhere but to each their own. The code should be consistent in its style for ease of reading.

Closing the question, it seems you finally solved it.

Again, the problem is in your if condition, not with negative numbers.

I don't really know the best ways for C++, but with the given C++ template you can do something simple, like:

static long findMissing(std::vector<long> list) {
  std::cout << "List: ";
  for (int i = 0; i < list.size(); i++) std::cout << list[i] << ", ";
  std::cout << "\n";
  return list[0];
}

Don't print stuff in tests suite, print it in your function. For C++ you should know about std::cout.

Well, now you see your code isn't right, so fix it. I've already told you where to look.

Assert::That(findMissing(std::vector<long>{1, 5, 7}), Equals(3));

And with this one?

Don't just make up inputs, test with them, and call it a day. Check the actual inputs, and test these in your VS.

No idea, are you testing it there with the same input values that are used here?

Assert::That(findMissing(std::vector<long>{1, 3, 7}), Equals(5));

Your if condition seems to be true for all the elements of the serie.

Not a kata issue, please use Question label when the problem is in your code:

C++ Completions 1628

Read this: https://github.com/codewars/codewars.com/wiki/Troubleshooting-your-solution#how-do-i-post-to-a-kata-discourse

Your if condition is wrong.

The tests are ok, with different items it means you can't use the same number (for instance the same 2 that is in the position 0) as your code does. Your code is returning {0, 0}.

It's not returning only {0,0} there is a test (the last sample test) that your code fails, and that's because your loops are wrong.

target will always be the sum of two different items from that array

Check this too: https://github.com/codewars/codewars.com/wiki/Troubleshooting-your-solution

For problems with your code use Questionnot Issue label.