class Matrix{
public:
    Matrix(int, int);                       // constructor
    Matrix(const Matrix&);                  // copy constructor

    Matrix& operator+= (const Matrix&);
    Matrix& operator-= (const Matrix&);
    int* operator[] (int) const;

private:
    int rows;
    int cols;
    int** Mat_p;
};

Matrix& Matrix::operator+= (const Matrix& M){
    for (int indexR = 0; indexR < rows; ++indexR)
        for (int indexC = 0; indexC < cols; ++indexC)
            Mat_p[indexR][indexC] += M[indexR][indexC];
}

Matrix& Matrix::operator-= (const Matrix& M){
    for (int indexR = 0; indexR < rows; ++indexR)
        for (int indexC = 0; indexC < cols; ++indexC)
            Mat_p[indexR][indexC] -= M[indexR][indexC];
}