Перегрузка оператора ()

class Matrix
{
    public:
        Matrix(unsigned int SizeOfMatrix);
        virtual ~Matrix();
       /.../
        int* operator() (unsigned int i, unsigned int j);
 
    private:
        unsigned int size;
        int **PtrToMatrix;
};
 
Matrix::Matrix(unsigned int SizeOfMatrix)
{
    int i,j;
    size=SizeOfMatrix;
    PtrToMatrix = new int *[size];
    for(i=0;i<size;i++)
    {
        PtrToMatrix[i]=new int[size-i];
        for(j=0;j<(size-i);j++)
        {
            PtrToMatrix[i][j]=size-i-j;
        }
    }
}
 
int Matrix::operator() (unsigned int i, unsigned int j)
{
    if( (i>=size) || (j>=size) ) return NULL;
    if(j<=i) return PtrToMatrix[j][i-j];
    else return PtrToMatrix[i][j-i];
}

Matrix a(5);
a(2, 0) = 10;
cout << a(2,5)

int* Matrix::operator() (unsigned int i, unsigned int j)
{
    if( (i>=size) || (j>=size) ) return NULL;
    if(j<=i) return &PtrToMatrix[j][i-j];
    else return &PtrToMatrix[i][j-i];
}
*a(2,0)=10;

int    Matrix::operator() (unsigned int i, unsigned int j) const;
int&   Matrix::operator() (unsigned int i, unsigned int j);

int & Matrix::operator () ( unsigned int i, unsigned int j ) throw( std::out_of_range )
{
   if ( ! ( i < size  && j < size ) ) throw ( std::out_of_range( "Matrix::operator ()" ) );
   return ( PtrToMatrix[i][j] );
}
 
const int & Matrix::operator () ( unsigned int i, unsigned int j ) const throw( std::out_of_range )
{
   if ( ! ( i < size  && j < size ) ) throw ( std::out_of_range( "Matrix::operator ()" )  );
   return ( PtrToMatrix[i][j] );
}