Accessing an array out of bounds gives no error, why?

I am assigning values in a C++ program out of the bounds like this:

#include <iostream>
using namespace std;
int main()
{
    int array[2];
    array[0] = 1;
    array[1] = 2;
    array[3] = 3;
    array[4] = 4;
    cout << array[3] << endl;
    cout << array[4] << endl;
    return 0;
}

The program prints 3 and 4. It should not be possible. I am using g++ 4.3.3

Here is compile and run command

$ g++ -W -Wall errorRange.cpp -o errorRange
$ ./errorRange
3
4

Only when assigning array[3000]=3000 does it give me a segmentation fault.

If gcc doesn’t check for array bounds, how can I be sure if my program is correct, as it can lead to some serious issues later?

I replaced the above code with

vector<int> vint(2);
vint[0] = 0;
vint[1] = 1;
vint[2] = 2;
vint[5] = 5;
cout << vint[2] << endl;
cout << vint[5] << endl;

and this one also produces no error.