Trying to construct an object with another object as parameter - c++

Question

https://imgur.com/gallery/pEw8fBs
https://pastebin.com/xvWFHrTU
My errors are posted above..I don't understand what's wrong with this code..I'm trying to construct a book with a date object inside of it. Please help, this is my frist post as well!! :)
#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<cmath>
using namespace std;
inline void keep_window_open() { char ch; cin >> ch; }
class Date {
int y, m, d;
public:
Date(int d, int m, int y);
};
class Book {
string title;
string author;
string isbn;
Date date;
public:
Book(string t, string a, string id, Date d);
};
int main() {
Book Charlie("charlie", "gates", "333H", Date(1, 2, 3));
}

Answer 1

Both of your constructors are declared but not defined
class Date {
int y, m, d;
public:
Date(int _d, int _m, int _y) : y(_y), m(_m), d(_d) {} // definition
};
class Book {
string title;
string author;
string isbn;
Date date;
public:
Book(string t, string a, string id, Date d)
: title(t), author(a), isbn(id), data(d) {} // definition
};

Answer 2

Your problem will be solved if you declare a default constructor for Date:
#include <iostream>
#include <string>
using namespace std;
class Date {
int y, m, d;
public:
// Default constructor which will be used in 'Book'
Date() {}
// Don't semicolon here, just two braces required
Date(int d, int m, int y) {}
};
class Book {
string title;
string author;
string isbn;
// Default constructor called here
Date date;
public:
// You can code everything inside the braces now
// NOTE 2: Default constructor called here
Book(string t, string a, string id, Date d) {}
};
int main() {
Book Charlie("charlie", "gates", "333H", Date(1, 2, 3));
return 0;
}