I've been doing the same! It certainly helps for strings. Pointer block diagrams (like K&R use) seem to help too. Mostly what melts their brains is the idea that an identifier can be "in two places at once" - for example, you can have a variable x declared in some scope and a function one of whose arguments is named x, and those are two different things.
Try explaining the concept of "scope", starting with nested blocks. It does require some practice. I suggest not unnecessarily reusing identifiers associated with different objects.
