How to convert int to const int to assign array size on stack?

Question

I am trying to allocate a fixed size on stack to an integer array

#include
using namespace std;

int main(){

    int n1 = 10;
          


        

Answer 1

How should I typecast n1 to treat it as a const int?

You cannot, not for this purpose.

The size of the array must be what is called an Integral Constant Expression (ICE). The value must be computable at compile-time. A const int (or other const-qualified integer-type object) can be used in an Integral Constant Expression only if it is itself initialized with an Integral Constant Expression.

A non-const object (like n1) cannot appear anywhere in an Integral Constant Expression.

Have you considered using std::vector<int>?

[Note--The cast is entirely unnecessary. Both of the following are both exactly the same:

const int N = n1;
const int N = const_cast<const int&>(n1);

--End Note]

Answer 2

Only fixed-size arrays can be allocated that way. Either allocate memory dynamically (int* foo = new int[N];) and delete it when you're done, or (preferably) use std::vector<int> instead.

(Edit: GCC accepts that as an extension, but it's not part of the C++ standard.)