LMS error no operator = matches these operands - c++

Question

So for practice purposes I am creating a library management system using composition, to understand and practice the concept of composition.so i have a book class and a user class. i am composing a pointer of book class in the user class. i am using dma (dynamic memory allocation) for the add function.but i am getting this error that i am unable to debug.
Error (active) E0349 no operator "=" matches these operands PRAcTice
here's the whole code for understanding
#ifndef LMS_H
#define LMS_H
#include <iostream>
#include <string>
using namespace std;
class book {
private:
string bname;
int ISBN;
string author;
string publisher;
public:
book(string n = " ", int i = 0, string a = " ", string p = " ") {
bname = n;
ISBN = i;
author = a;
publisher = p;
}
void setbname(string a) {
bname = a;
}
string getbname() {
return bname;
}
void setisbn(int b) {
ISBN = b;
}
int getisbn() {
return ISBN;
}
void setauthor(string c) {
author = c;
}
string getauthor() {
return author;
}
void setpublisher(string d) {
publisher = d;
}
string getpublisher() {
return publisher;
}
friend ostream & operator << (ostream & COUT, book & rhs);
};
ostream & operator << (ostream & COUT, book & rhs) {
COUT << "Book Name: " << rhs.getbname() << endl;
COUT << "ISBN: " << rhs.getisbn() << endl;
COUT << "Author: " << rhs.getauthor() << endl;
COUT << "Publisher: " << rhs.getpublisher() << endl;
}
class user {
private:
string name;
int id;
string password;
book * b;
int bno;
public:
user(string m = " ", int q = 0, string n = " ", book * bx = NULL, int no = 0) {
name = m;
id = q;
password = n;
b = bx;
}
void setname(string a) {
name = a;
}
string getbname() {
return name;
}
void setid(int b) {
id = b;
}
int getid() {
return id;
}
void setpassword(string c) {
password = c;
}
string getpassword() {
return password;
}
void setbno(int d) {
bno = d;
}
int getisbn() {
return bno;
}
void setbook(book a[]) {
b = new book[bno];
for (int i = 0; i < bno; i++) {
b[i].setbname(a[i].getbname());
b[i].setisbn(a[i].getisbn());
b[i].setauthor(a[i].getauthor());
b[i].setpublisher(a[i].getpublisher());
}
}
book * getbook() {
return b;
}
book * add(book b) {
b = new book[bno + 1];
}
};
#endif // !"LMS_H"

Answer 1

The problem is that the object b on the left hand side of the assignment b = new book[bno + 1]; is of type book while the object on the right hand side is of type book*.
//---v----------------------->type of object b is book
b = new book[bno + 1];
//-------^^^^^^^^^^^^^^^^----type of the resulting object on rhs is book*
That is there is a mismatch in the type on the left hand side and right hand side of the assignment and since there is no overloaded operator= that has parameter of type book and book* you get the mentioned error.
Additionally you're missing return statements inside operator<< and inside add.