Question

Here is a simple code of defining an array. I noticed this code will work(compile and run) under Linux(OpenSue,gcc compiler), but it will not work under Windows system. The compiler gave error prompt. Does anybody know the reason? Thanks!

#include <iostream>
using namespace std;

int main()
{
    int N;
    cin>>N;
    int ar[N];
    ar[0]=0;
    cout<<"ar[0]= "<<ar[0]<<endl;
    return 0;
}

Answer 1

The code isn’t valid C++ since C++ does not allow declaring a (stack-allocated) array with a variable size as you do. The reason for this is that C++ offers better mechanisms of declaring dynamically sized arrays, using the std::vector class from its standard library:

#include <iostream>
#include <vector>

using namespace std;

int main()
{
    int N;
    cin >> N;
    vector<int> ar(N);
    ar[0] = 0;
    cout << "ar[0] = " << ar[0] << endl;
    return 0;
}

g++ (the compiler you used on Linux) by default allows this through a compiler extension.