/in/ex4.cpp: In member function 'virtual int bookInventory::searchBook(const string&) const':
/in/ex4.cpp:16:18: 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:25:22: 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::removeBook(int)':
/in/ex4.cpp:48:23: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     for(int i = ID-1;i<numBooks-1;i++){
                      ~^~~~~~~~~~~
/in/ex4.cpp: In member function 'virtual void bookInventory::printInventory() const':
/in/ex4.cpp:57:18: 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:71:28: error: statement has no effect [-Werror=unused-value]
     books[ID-1].isAvailable==false;
     ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
/in/ex4.cpp: In member function 'void library::returnBook(int)':
/in/ex4.cpp:77:28: error: statement has no effect [-Werror=unused-value]
     books[ID-1].isAvailable==true;
     ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
/in/ex4.cpp: In member function 'void library::listBorrowed() const':
/in/ex4.cpp:82:18: 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