/in/ex4.cpp: In member function 'virtual int bookInventory::searchBook(const string&) const':
/in/ex4.cpp:13:18: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     for(int i=0;i<numBooks;i++)
                 ~^~~~~~~~~
/in/ex4.cpp: In member function 'virtual void bookInventory::setBook(const Book&, int)':
/in/ex4.cpp:21:15: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     else if(ID<=numBooks)
             ~~^~~~~~~~~~
/in/ex4.cpp: In member function 'virtual Book bookInventory::viewBook(int) const':
/in/ex4.cpp:28:17: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     if(ID<=0||ID>numBooks) throw Exception("Invalid book ID.");
               ~~^~~~~~~~~
/in/ex4.cpp: In member function 'virtual void bookInventory::removeBook(int)':
/in/ex4.cpp:33:17: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     if(ID<=0||ID>numBooks) throw Exception("Invalid book ID.");
               ~~^~~~~~~~~
/in/ex4.cpp:34:21: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     for(int i=ID-1;i<numBooks;i++)
                    ~^~~~~~~~~
/in/ex4.cpp: In member function 'virtual void bookInventory::printInventory() const':
/in/ex4.cpp:41:18: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     for(int i=0;i<numBooks;i++){
                 ~^~~~~~~~~
/in/ex4.cpp: In member function 'void library::borrowBook(int)':
/in/ex4.cpp:53:17: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     if(ID<=0||ID>numBooks) throw Exception("Invalid book ID.");
               ~~^~~~~~~~~
/in/ex4.cpp: In member function 'void library::returnBook(int)':
/in/ex4.cpp:59:17: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     if(ID<=0||ID>numBooks) throw Exception("Invalid book ID.");
               ~~^~~~~~~~~
/in/ex4.cpp: In member function 'void library::listBorrowed() const':
/in/ex4.cpp:66:18: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     for(int i=0;i<numBooks;i++)
                 ~^~~~~~~~~
cc1plus: all warnings being treated as errors
/in/compile/Makefile:26: recipe for target 'ex4.o' failed
make: *** [ex4.o] Error 1