Manas Bhardwaj is totally right!
But at least try to search for yourself.
Ah... you know google? Well, look what it has given to me for you:
http://cybergrouch.blogspot.hu/2012/03/non-recursive-binary-tree-traversal.html[
^]. But don't even dream to give that code as your homework, since your tutor will know, that it is too advanced for you. Still, you can compile and debug/trace it, and see how it works.