void dfs()
        {
            Stack * helper_stack = new Stack();
            vertexList[0].wasVisited = true;
            displayVertex(0);
            helper_stack->push(0);

            int v;
            while (!helper_stack->isEmpty()) //while stack is not empty
            {
                getAdjacentUnvisitedVertex(v);
            }
            if (v==(-1))
            {
                helper_stack->pop();
            }
            else
            {
                vertexList[v].wasVisited=true;
                displayVertex(v);
                helper_stack->push(v);
            }
            for(int j=0; j<n_vertices; j++)
                vertexList[j].wasVisited = false;
        }