In C++ books, array bound must be constant expression, but why the following code works?

Question

#include 
using namespace std;

int main(){
    int n=10;
    int a[n];

    for (int i=0; i

        

Answer 1

That is C99 feature that allows VLA (variable length array).

Compile it with g++ -pedantic, I'm sure that wouldn't compile.

Answer 2

This a a C99 feature called VLA which some compilers also allow in C++. It's allocation on stack, just as it would be with int a[10].