Thanks by the answer!

I was so naive trusting in your tests...

For the ones comming after this point: Don't forget 'everything is a lie'! (even this, maybe)

There must be a problem with the tests in c++...
My code can only returns the sum or the product (if/else case).
But the test passing 2 and 2 failed (expected 4, actual 2).
It is not possible! Can you verify this problem for me, please?