Question

Only constants can be used to declare the size of automatic and static
arrays. Not using a constant for this purpose is a compilation error.

Says Pearson.

However, following works fine. According to Pearson, it should not work (I think). Can you help me to understand this?

#include <iostream>
using namespace std;

int main()
{
    int in;
    cin >> in;
    int a[in];

    a[4] = 412;
    int i = 0;
    while(i<5){
    cout << i << ":" << a[i] << endl;
    i++;
    }
}

Answer 1

That’s an extension to C++ that’s found in the GNU compiler, but it doesn’t conform to the C++ standard. If you compile your code using g++ -std=c++98, the compiler should complain.