I'm suprised that std::cout << arr.end(); does not print the integer index of +1 of the array. I think it's for 2 reasons.
1 - arr.end() returns a const expr, which is actually indexed +1 from the last element in the array.
2 - As it's a constant we can't alter it's position.
Am I right? I know how to return values from certain elements in the array. I'm struggling with existing libraries atm. I know their benefits, but struggling with existing libraries atm.
I can't understand your question. Of course you can't change where end() points. Why would you want to? It looks like you might actually want something like this:
1 2 3 4 5 6 7 8 9 10
#include <algorithm>
#include <array>
#include <iostream>
int main()
{
std::array<int,6> arr{ 13, 90, 99, 5, 40, 80 };
auto found = std::find(arr.begin(), arr.end(), 15);
std::cout << std::distance(arr.begin(), found) << '\n'; // prints 6
}