Why does this code work?

Question

One of the challenges in c++ describes that the output of
std::cout << 1["abc"] << endl;
is 'b', or if you replace the '1' with a '2' the output is 'c' --> so the number indicates the index in the 'array' ["abc"]. But I am not aware that you can declare an array with ["abc"] and access the elements by prepending the index.
So what code will the compiler generate?

Answer 1

Ok, I found the explanation on stackoverflow: https://stackoverflow.com/questions/381542/with-arrays-why-is-it-the-case-that-a5-5a

Answer 2

Anna now you rewrote it, first and third line are regular c++ using the subscript operator to access elements of a regular c++-array. But why does the second line work, this really surprises me.

Answer 3

https://code.sololearn.com/c4KyMv8C5qTs/?ref=app