myArray[N] where N = 1,000,000 returns an error whereas myArray[1,000,000] doesn't

Question

File extension: .cpp

I have the following code:

int main() {
    int N; cin >> N;
    int myArray[N];
    return 0;
}

I get an error when I'm trying to run that program if I input N as 1,000,000. However, when I set myArray[N] to myArray[1000000], it doesn't. Why does this happen?

Answer 1

int myArray[N]; is not valid in C++. This behavior was introduced in C99 but never in C++, possibly because it causes a lot of ugly stuff to happen behind the scenes in order to make it work, and it would make the generated code less efficient as a result. In fact this feature was even reversed in C11 where its support is merely optional and not mandatory anymore. Use std::vector<int> instead, or any similar standard container of your choice.