int hasCycle(Graph g)
{
   visited = calloc(g->nV,sizeof(int));
   int result = dfsCycleCheck(g, 0, 0);
   free(visited);
   return result;
}

int dfsCycleCheck(Graph g, Vertex v, Vertex prev)
{
   visited[v] = 1;
   Vertex w;
   for (w = 0; w < nV(g); w++) {
      if (hasEdge(v,w)) {
         if (!visited[w])
            return dfsCycleCheck(g, w, v);
         else if (w != prev)
            return 1; // found cycle
      }
   }
   return 0; // no cycle at v
}

// but still has a bug (or at least an assumption)
// what is it? how to fix?