Something

#include<iostream>
#include<string>

using namespace std;

// Book Class
class Book{
   protected:
      string title;
      string publicationYear;
      string author;
   public:
      
      Book(const string title, const string pubYear, const string author);
      void displayValues();
};
// Book Constructor
Book::Book(const string title, const string pubYear, const string author)
{
    this->title = title;
    this->publicationYear = pubYear;
    this->author = author;
}
// displayValue function
void Book::displayValues() 
{
    cout<<"Title: "<<title<<" Year: "<<publicationYear<<" Author: "<<author<<endl;
}

// BookInventory Class
class BookInventory : public Book{
                    friend BookInventory operator+(BookInventory, int);
                    public:
                           BookInventory(const string title, const string pubYear, const string author, int totInv); // constructor
                           void displayValues(); // overloaded function
                    protected:
                           int totalInventory;
      };
BookInventory::BookInventory(const string title, const string pubYear, const string author, int totInv) : Book(title, pubYear, author)
{
    this->totalInventory = totInv;                           
}
void BookInventory::displayValues()
{
    cout<<"Title: "<<title<<" Year: "<<publicationYear<<" Author: "<<author<< " Inventory: " << totalInventory << endl;                      
}
BookInventory operator+(BookInventory book, int invAdd) // this probably wont work....
{
    int total;
    total = book.totalInventory + invAdd;  
}
int main()
{
    BookInventory book1 = BookInventory("C++ Programming Guide", "2006", "Milton Jones",10);
    book1.displayValues();
    cout<<"Adding 10 to inventory."<<endl;
    book1 = book1 + 10;
    book1.displayValues();
   
    cout<<"Subtracting 10 from inventory."<<endl;
    //book1 = book1 - 10;
    book1.displayValues();
    system("pause");
    return 0;
}