/in/HW7.cpp: In function 'int returnbook(std::__cxx11::string&, customer*, library*)':
/in/HW7.cpp:99:41: error: unused parameter 'customer' [-Werror=unused-parameter]
 int returnbook(string &bookID,customer *customer,library *library){
                                         ^~~~~~~~
cc1plus: all warnings being treated as errors