You have my sympathy. I must have wasted an hour or more last night before I took the trouble to Google "Arduino struct" and found out about the need for a .h file from the Playground article.
[ rant]
I really detest the way C/C++ requires this sort of fragmentation of the program code. I was trying to figure out the logic of another program and I was constantly jumping between three different files.
I don't mind having different parts of the logic in different files as that generally makes the files shorter and easier to follow. But having to put different parts of the same piece of logic in different files is ridiculous. [ /rant].
...R