数组访问越界

#include <iostream>

using namespace std;

int main() {
    int num_array[5];

    for (int idx = -1; idx <= 5; idx++) // out of bounds
        num_array[idx] = idx * idx;

    for (int idx = -1; idx <= 5; idx++) // out of bounds
        cout << "num_array[" << idx << "] = " << num_array[idx] << endl;

    return 0;
}