736: Mainline

Because add works on header objects, add is a member function of the header class. Because add adds a pointer to a new railroad_car object, provided as an ordinary argument, add must have a parameter that is declared to be a pointer to a railroad_car object. Because there is to be no return value, add's return type is void:

class header {
  public:  link *first_link_pointer;
           header ( ) {
             first_link_pointer = NULL;
           }
           void add (railroad_car *new_element) {  
             ...                                   
           }                                       
           ... 
};