My program is almost done. However, when trying the second and third option the program returns to the main menu instead of calling the next function. The only function working properly is the cashier, and that is because it does not open another function, it keeps using a loop or exiting the program.
I just messed around with it a little. If you select "Inventory Database Module" it pulls up the inventory database as expected, but then all of the function calls from there do nothing but print a single line.
lookUpBook(), addBook(), editBook(), and deleteBook() do nothing but print a single string.
Is this as intended or did you forget to add function calls?
Same thing in report. The if block under the comment "respond to the user's selection" only prints out a single line.
EDIT: On an unrelated note, if this is your full code I don't think mainmenu.h is actually doing anything.