class Book{
  //field: isbnNo, title, price;
  //string *autherPtr; int authorNo;
public:
  //write default constructor
  //add other necessary member functions...
  //declare necessary friend functions...
  friend istream& operator>>(istream, Book&);
  bool operator<(float f){ ... }
  void operator+=(int x){...}
  float operator+(Book b){     }
  friend float operator+(float, Book);

};

//need to overload >> operator to allow chaining
//Should ask info for all the fields from user

//need to overload << operator to allow chaining
//Should display all the fields of the object iff
//the default values are replaced with user input

int main(){
  int n, i; cout<<"How many books? "; cin>>n;
  Book bookArr[n]; //an array of Book objects

  int noOfAuthors = populateBooks(bookArr, n);
  //write this global function
  //This function will replace the default values (set by constructor) of
  //n Books by using cin>>BookObject format in a loop. Finally it returns
  //total number of authors of all books of the array.

  cout<<”No of authors of all books is: “<<noOfAuthors<<endl;
  cout << “Detail of the books are: “ << endl;
  for(i=0; i<n ;i++) cout << bookArr[i] << endl;
  int index = getBookIndexWithLowestPrice(bookArr, n);
  int x; cout<<"% to increase lowest price: "; cin>>x;

  if(bookArr[index]<500.0) bookArr[index] += x;
  //bookArr[index] is a book and if it’s
  //price is <500 taka, then += will increase
  //the book’s price by x%. Write necessary
  //operator functions ( < , += )

  Book b1, b2, b3, b4; cin>>b1>>b2>>b3>>b4;

  //overload ‘+’ operator twice.
  //‘+’ means adding price, not books
  cout<<( (b1+b2+b3+b4 > 5000.0)
    ? "Customer is given 10% discount."
    : " customer is given 5% discount."
  ) << endl;
  return 0;
}
----------------------
//global
istream& operator>>(istream& in, Book& b){
      cin>>b.isbn; getline(in, b.title);
      ....
      cin>>authorNo;
      autherPtr = new string[authorNo];
      loop: authorNo times{
	 getline(in,autherPtr[i]);
      }
      return in;
}

int populateBooks(Book arr[] , int size ){
	int totalAuthNo=0;
	loop: size times{
		//arr[i].setBookInfo();
		cin>>arr[i];
		totalAuthNo += arr[i].getAuthorNo();
	}
	return totalAuthNo ;
}





b1+b2+b3+b4 > 5000.0

b1+b2 -> object+object return a float (say sum)

sum + b3