$//$ Initializes an iterator to the beginning of a tree $($i$.$e$.,$ first in$-$order node$)$

void tree$\_$iterator$\_$begin$($tree$\_$iterator$\_$t$*$ iter, tree$\_$node$\_$t$*$ root$)$

$\{$ typedef struct tree$\_$node $\{$

shape$\_$t$*$ shape; $//$ Shape associated with the node

struct tree$\_$node$*$ left; $//$ Left subtree

struct tree$\_$node$*$ right; $//$ Right subtree

$\}$ tree$\_$node$\_$t;