It should be in the arguments of the function.

when you click on TRAIN you get the kata trainer, where the declaration for the function odd_or_even is provided:

#include <string>
#include <vector>

std::string odd_or_even(const std::vector<int> &arr)
{
    return ""; // your code here
}

...and you write your code between the curly braces in place of the line that says, "your code here"

So this is my first problem to solve on this website and I know how to solve it
but I just dont understand where i should write the solution.

any tips ?