oop – expected ‘,’ or ‘…’ before ‘&=’ token (C++)

I am trying to learn c++ and I have come across an exercise that is giving me quite a bit of trouble. The compiler is giving me a number of errors, in particular the following:

expected ',' or '...' before '&=' token
         Book(int=0, const string&=" ", const string&=" ", int=0, const string&=" ", double=0.0);

Could you help me? I enclose my code.

//Book.h This is the base class

#ifndef BOOK_H
#define BOOK_H

#include <iostream>
#include <string>
#include <stdexcept>
#include <sstream>
#include <vector>
#include <algorithm>
#include "Date.h"
using std::cout;
using std::cin;
using std::endl;
using std::string;
using std::ostringstream;
using std::invalid_argument;
using std::out_of_range;
using std::vector;
using std::sort;

class Book{
    public:    
        //Costruttore
        Book(int=0, const string&=" ", const string&=" ", int=0, const string&=" ", double=0.0);
        virtual ~Book()=default;
        //Funzioni Set
        void setId(int);
        void setAuthors(const string&);
        void setTitle(const string&);
        void setYear(int);
        void setPosition(const string&);
        void setValue(double);
        //Funzioni Get
        int getId() const;
        string getAuthors() const;
        string getTitle() const;
        int getYear() const;
        string getPosition() const;
        double getValue() const;
        //Funzione Stampa
        virtual void print() const;
        //Overloading di operatori utili per l'ordinamento
        bool operator<(const Book& sec) const;

    protected:
        int book_id, year;
        string authors, title, position;
        double value;

};

#endif

//Book.cpp, implementation of Book.h
#include "Book.h"

//Costruttore
Book::Book(int id, const string& aut, const string& t, int y, const string& pos, double val){
    setId(id);
    setAuthors(aut);
    setTitle
    setYear(y);
    setPosition(pos);
    setValue(val);
}

//Funzioni SET
void Book::setId(int id){
    book_id=id;
}

void Book::setAuthors(const string& aut){
    authors=aut;
}

void Book::setTitle(const string& t){
    title=t;
}

void Book::setYear(int y){
    if(y<=0 || y>2022)
        out_of_range("L'anno deve essere compreso fra 1 e 2022");
    else
        year=y;
}

void Book::setPosition(const string& pos){
    position=pos;
}

void Book::setValue(double val){
    if(val<0)
        out_of_range("Il valore deve essere maggiore o uguale a 0.");
    else
        value=val;
}

//Funzioni GET
int Book::getId() const{
    return this->book_id;
}

string Book::getAuthors() const{
    return this->authors;
}

string Book::getTitle() const{
    return this->title;
}

int Book::getYear() const{
    return this->year;
}

string Book::getPosition() const{
    return this->position;
}

double Book::getValue() const{
    return this->value;
}

//Funzione STAMPA
void Book::print() const{
    cout<<"Nome Libro: "<<getTitle()<<
    "nAutori: "<<getAuthors()<<
    "nID: "<<getId()<<
    "nAnno di pubblicazione: "<<getYear()<<
    "nPosizione in libreria: "<<getPosition()<<
    "nValore: "<<getValue()<<"$"<<endl;
}

/*
Overloading <
La traccia ci chiede di ordinare per autore, se l'autore
coincide allora bisogna ordinare per anno di pubblicazione.
*/
bool Book::operator<(const Book& sec) const{
    if(authors==sec.authors) return this->year<sec.year;
    else return this->authors<sec.authors;
}


//Borrow.h This is the derived class
#ifndef BORROW_H
#define BORROW_H
#include "Book.h"


class Borrow : public Book{
    public:
        //Dovrà avere due costruttori, uno con data di restituzione standard (30 giorni dopo la data di prestito)...
        Borrow(int, const string&, const string&, int, const string&, double, const Date&);
        virtual ~Borrow()=default;
        //Funzioni SET
        void setDueDate(const Date&);
        //Funzioni GET
        Date getDueDate() const;

        //...L'altro con data di resituzione diversa
        //Borrow(const Book&, Date, Date);
        //Operatore < per l'ordinamento
        //bool operator<(const Borrow&) const;
        //Funzione per la stampa, sarà un override poiché è già presente nella classe base

        virtual void print() const override;

    protected:
        Date collectDate; //Giorno in cui il libro viene preso in prestito
        Date dueDate;     //Giorno in cui il libro deve essere restituito
};

//Borrow.cpp
#include "Borrow.h"

Borrow::Borrow(int id, const string& aut, const string& t, int y, const string& pos, double val, const Date& dat){
    collectDate=dat;
    setDueDate(dat);
}

void Borrow::setDueDate(const Date& dat){
    for(int i=0; i<30; i++){
        dat++;
    }
    dueDate=dat;
}
/*
Borrow::Borrow(const Book& b, Date datOne, Date datTwo){

    collectDate=datOne;
    dueDate=datTwo;
}
*/

void Borrow::print() const{
    
    cout<<"Preso in prestito il: "<<collectDate<<endl;
    cout<<"Da restituire il: "<<getDueDate()<<endl;
}

Date Borrow::getDueDate() const{
    return dueDate;
}

//Makefile
CC=g++
CFLAGS=-std=c++11
DEPS= Book.h Borrow.h Date.h
OBJ= Book.o Borrow.o Date.o main.o

%.o: %.cpp $(DEPS)
    $(CC) -c -o $@ $< $(CFLAGS)
esegui: $(OBJ)
    $(CC) -o $@ $^ $(CFLAGS)
clean: $(OBJ)
    rm -f *.exe *.o

//Compiler error
In file included from Book.cpp:1:0:
Book.h:24:33: error: expected ',' or '...' before '&=' token
         Book(int=0, const string&=" ", const string&=" ", int=0, const string&=" ", double=0.0);
                                 ^~
Book.h:24:9: error: default argument missing for parameter 2 of 'Book::Book(int, std::__cxx11::string)'
         Book(int=0, const string&=" ", const string&=" ", int=0, const string&=" ", double=0.0);
         ^~~~
Book.cpp:4:1: error: prototype for 'Book::Book(int, const string&, const string&, int, const string&, double)' does not match any in class 'Book'
 Book::Book(int id, const string& aut, const string& t, int y, const string& pos, double val){
 ^~~~
In file included from Book.cpp:1:0:
Book.h:21:7: error: candidates are: Book::Book(const Book&)
 class Book{
       ^~~~
Book.h:24:9: error:                 Book::Book(int, std::__cxx11::string)
         Book(int=0, const string&=" ", const string&=" ", int=0, const string&=" ", double=0.0);
         ^~~~
make: *** [Book.o] Error 1