Add preorder traversal example

Octree/examples/Octree/Octree_build_from_Point_set.cpp

@@ -27,7 +27,7 @@ int main(int argc, char **argv) {
     std::cerr << "Error: cannot read file" << std::endl;
     return EXIT_FAILURE;
   }
-  std::cout << "loaded " << points.number_of_points() << " points" << std::endl;
+  std::cout << "loaded " << points.number_of_points() << " points\n" << std::endl;
 
   // Create an octree from the points
   Octree octree(points, points.point_map());

Octree/examples/Octree/Octree_traversal_preorder.cpp

@@ -0,0 +1,45 @@
+#include <fstream>
+#include <iostream>
+
+#include <CGAL/Simple_cartesian.h>
+#include <CGAL/Octree.h>
+#include <CGAL/Octree/IO.h>
+#include <CGAL/Point_set_3.h>
+#include <CGAL/Point_set_3/IO.h>
+
+// Type Declarations
+typedef CGAL::Simple_cartesian<double> Kernel;
+typedef Kernel::Point_3 Point;
+typedef CGAL::Point_set_3<Point> Point_set;
+typedef Point_set::Point_map Point_map;
+typedef CGAL::Octree::Octree<Point_set, Point_map> Octree;
+
+int main(int argc, char **argv) {
+
+  // Point set will be used to hold our points
+  Point_set points;
+
+  // Load points from a file.
+  std::ifstream stream((argc > 1) ? argv[1] : "data/cube.pwn");
+  stream >> points;
+  if (0 == points.number_of_points()) {
+
+    std::cerr << "Error: cannot read file" << std::endl;
+    return EXIT_FAILURE;
+  }
+  std::cout << "loaded " << points.number_of_points() << " points\n" << std::endl;
+
+  // Create an octree from the points
+  Octree octree(points, points.point_map());
+
+  // Build the octree
+  octree.refine();
+
+  // Print out the octree using preorder traversal
+  for (auto &node : octree.walk<CGAL::Octree::Traversal::Preorder>()) {
+
+    std::cout << node << std::endl;
+  }
+
+  return EXIT_SUCCESS;
+}