How do compilers treat variable length arrays

Question

This might seem like a beginner\'s question, but I am interested in the way that a compiler normally creates arrays of variable-dimensions, like in the following program.

Answer 1

int main(){
  int n;
  std::cin>>n;
  int a[n];
}

This is not legal C++. G++ accepts Variable Length Array's as an extension but VLAs are not part of the C++ standard. They are part of the C99 standard which GCC supports(I am not sure to what extent) but MSVC doesn't.