template<typename vertex>
class directed_graph
{
    private:
            std::vector<std::vector<bool> > adj_matrix;
            size_t size;
            int num_of_vertices;

    public:
            void add_vertex(const vertex&);
            void add_edge(const vertex&, const vertex&);
}


template <typename vertex>
void directed_graph<vertex>::add_vertex(const vertex& u)
{
int newVertexNumber = num_of_vertices;
num_of_vertices++;

for(int i = 0; i<num_of_vertices; i++)
{
    adj_matrix[i][newVertexNumber] = false;
    adj_matrix[newVertexNumber][i] = false;
}

newVertexNumber = u;

}


template <typename vertex>
void directed_graph<vertex>::add_edge(const vertex& u, const vertex& v)
{
 if ((u >= 0) && (u < size) && (v >= 0) && (v < size) && (u != v))
     {
    adj_matrix[u][v] = true;
    adj_matrix[v][u] = true;
 }
}