If you are using the main C++ distribution of wxWidgets, Feel free to ask any question related to wxWidgets development here. This means questions regarding to C++ and wxWidgets, not compile problems.
Rather than using numbers I suggest using wxDateTime::Jan, wxDateTime::Feb, etc. because there is no guarantee that wxDateTime::Jan will always equal 0. You can also easily add directly to wxDateTime::Jan if you need to iterate through or specifiy arbitrary months.