// declare the graph object
//
DiGraph<Char> graph(DstrBase::USER);

// perform the required assignments
//
Char* chr_a = new Char(L'a');
GraphVertex<Char>* vertex_a = graph.insertVertex(chr_a);
graph.insertArc(graph.getStart(), vertex_a, true);

Char* chr_b = new Char(L'b');
GraphVertex<Char>* vertex_b = graph.insertVertex(chr_b);
graph.insertArc(graph.getStart(), vertex_b, true);

Char* chr_c = new Char(L'c');
GraphVertex<Char>* vertex_c = graph.insertVertex(chr_c);
graph.insertArc(graph.getStart(), vertex_c, true);

Char* chr_d = new Char(L'd');
GraphVertex<Char>* vertex_d = graph.insertVertex(chr_d);
graph.insertArc(graph.getStart(), vertex_d, true);                     
      
// connect two vertices using the insertArc method
//
graph.insertArc(vertex_a,vertex_d, false, (float)0.7);
graph.insertArc(vertex_b, vertex_d, false, (float)0.9);
graph.insertArc(vertex_c, vertex_d, false, (float)3.7);
graph.insertArc(vertex_d, graph.getTerm(), true);

// clean up allocated memory
//
graph.clear(Integral::FREE);

  // declare the graph object
  //
  DiGraph<Long> index_graph;

  // first read the graph that defines the connections
  //
  if (!index_graph.read(sof_a, graph_tag_a)) {
    return Error::handle(name(), L"readRecipeGraph", Error::READ, __FILE__,
			 __LINE__, Error::WARNING);
  }

  SingleLinkedList<Long> node_indices(DstrBase::USER);
  SingleLinkedList< Triple< Pair<Long, Long>, Float, Boolean> > topo;
  index_graph.get(node_indices, topo);

  // sanity check -- the nodes should be consecutive integers
  //
  long count = 0;
  for (boolean m = node_indices.gotoFirst(); m; m = node_indices.gotoNext()) {
    if (node_indices.getCurr()->ne(count++)) {
      return Error::handle(name(), L"readRecipeGraph", ERR, __FILE__, 
                           __LINE__);
    }
  }

  // boolean values to represent if the node has parents
  //
  boolean no_parents[count];  

  for (long i = 0; i < count; i++)
      no_parents[i] = true; // initialization to no parents
  
  // iterate over all vertices in the list to test if a node has parents
  //
  for (boolean more = topo.gotoFirst(); more;  more = topo.gotoNext()) {

    // retrieve the destination vertex position of the current arc
    // the node located in second place always has parents
    //
    Long dst_pos = topo.getCurr()->first().second();
    no_parents[(long)dst_pos] = false;
  }

  for (long i = 0; i < count; i++)
    {
      if(no_parents[i] == true)
	printf("node #%ld : (**no** parent)\n", i);
      else
	printf("node #%ld : (parents exist)\n", i);
    }  

------------------------------
Input file for above code:
@ DiGraph<Long> 0 @
weighted = true;
vertices =
        {0, {0}},
        {1, {1}},
        {2, {2}},
        {3, {3}},
        {4, {4}},
        {5, {5}},
        {6, {6}},
        {7, {7}};
arcs =
        {0, 2, 0},
        {1, 3, 0},
        {2, 4, 0},
        {3, 4, 1},
        {4, 5, 0},
        {6, 7, 0},
        {7, 4, 2};

--------------------------------
This is the output:

node #0 : (**no** parent)
node #1 : (**no** parent)
node #2 : (parents exist)
node #3 : (parents exist)
node #4 : (parents exist)
node #5 : (parents exist)
node #6 : (**no** parent)
node #7 : (parents exist)