operator+= Returns *this So Calls Chain

1#include <iostream>
2using namespace std;
3 
4class Wallet {
5    int m_cents;
6public:
7    Wallet(int cents) : m_cents(cents) {}
8    Wallet& operator+=(int cents) {
9        m_cents += cents;
10        cout << "now " << m_cents << endl;
11        return *this;
12    }
13    int cents() const { return m_cents; }
14};
15 
16int main() {
17    Wallet w(100);
18    (w += 50) += 25;
19    cout << w.cents() << endl;
20 
21    Wallet copy = (w += 5);
22    copy += 1;
23    cout << w.cents() << " " << copy.cents() << endl;
24    return 0;
25}