Overloading subscript operator [ ] for 2-d arrays

Array2D_AOOPS.cpp

#include <iostream>
#include <cstddef>

using namespace std;

template <typename T>
class Array2D {
    public:
        Array2D(size_t nr, size_t nc) : n_rows(nr), n_cols(nc), data(new T[n_rows*n_cols]) {}
        ~Array2D() { delete [] data; }
    private:
        class Helper {
                friend class Array2D;
            private:
                Helper(Array2D *array, size_t i_) : the_array(array), i(i_) {}
            public:
                T &operator[](size_t j) {
                    if (j >= the_array->n_cols) { cout << "OOR2" << endl; }
                    return *(the_array->data + i*the_array->n_cols + j);
                }
            private:
                Array2D *the_array;
                const size_t i;
        };
      //  friend class Helper;
    public:
        Helper operator[](size_t i) {
            if (i >= n_rows) { cout << "OOR1" << endl; }
            return Helper(this, i);
        }
    private:
        const size_t n_rows, n_cols;
        T *data;
};

int
main() {

    Array2D<int> a(3, 4);

    a[1][2] = 1234;
    cout << a[1][2] << endl;
    a[5][0] = 1;
    a[0][5] = 1;
}