Using const int as array size

Question

Why am I able to use a locally declared const int as the size of an array declaration but am not allowed to do the same with a const int passed as

Answer 1

Array size should be known at compile time.

const int with local variables may do not work neither if the value is not known at compile time as:

void f2(){
  const int dim = bar();
  int nums[dim];  // error
}

In Both case, const int tells that the value doesn't change, not that is it known at compile time.