The type names in the function declarations need to be pasted with the ##Titem
term too:
#define DO_LIST_HEADER(Titem,MAX) typedef struct {\
int count;\
Titem array[MAX];\
} TOrderedList##Titem;\
\
void initialize_list##Titem(TOrderedList##Titem *list);\
int insert_item##Titem(TOrderedList##Titem *list, Titem item);\
int retrieve_ith##Titem(const TOrderedList##Titem *list, int i, Titem *item);\
int number_of_items##Titem(const TOrderedList##Titem *list);\
int list_empty##Titem(const TOrderedList##Titem *list);