Add example on tree

example/ex-tree.c

@@ -0,0 +1,39 @@
+#include <stdio.h>
+#include "m-tree.h"
+
+TREE_DEF(tree, int)
+
+// Compute sum of the tree using iterator and a pre-order walk
+static int tree_sum_iter(tree_t t)
+{
+  int s = 0;
+  for(tree_it_t it = tree_it(t); !tree_end_p(it); tree_next(&it)) {
+    s += *tree_cref(it);
+  }
+  return s;
+}
+
+// Compute sum of the tree using recursive call
+static int tree_sum_recur(tree_it_t it)
+{
+  if (tree_end_p(it))
+    return 0;
+  if (tree_leaf_p(it))
+    return *tree_cref(it);
+  assert( tree_degree(it) == 2);
+  return *tree_cref(it) + tree_sum_recur(tree_down(it)) + tree_sum_recur(tree_right(tree_down(it)));
+}
+
+int main(void)
+{
+  tree_t t;
+  tree_init(t);
+  tree_it_t r = tree_set_root(t, 1);
+  tree_it_t l = tree_insert_child(r, 2);
+  tree_insert_child(r, 5);
+  tree_insert_child(l, 3);
+  tree_insert_child(l, 4);
+  printf("sum = %d vs %d\n", tree_sum_iter(t), tree_sum_recur(tree_it(t)));
+  tree_clear(t);
+  return 0;
+}