Entering the length of an array value?

Question

C++ / C#

Need it but it doesn't work

const int n;
cin >> n;
int arr[n];

Answer 1

The way you want to define an array is called VLA (Variable Length Array).
This joke only appeared in C99 and later. There are none in C++.
But even in C programs, not all compilers support them, for example, in MSVC, in my opinion, they have not yet been implemented. True, Microsoft does not claim full support for C standards.
So in C++, as already mentioned in the comments, use either dynamic arrays or std::vector.