The this Pointer

Inside every non-static member function, this is the address of the object the call runs on. You rarely write it — balance_ means this->balance_ — but you use it deliberately in three places.

#include <string>

class Account {
public:
    Account& deposit(long cents) {          // returning *this enables chaining
        balance_ += cents;
        return *this;
    }
    Account& withdraw(long cents) {
        balance_ -= cents;
        return *this;
    }
    bool same_as(const Account& other) const {
        return this == &other;               // identity: addresses compared
    }
    long balance() const { return balance_; }

private:
    long balance_{0};
};

// chaining: a.deposit(100).withdraw(30).deposit(5);

The three deliberate uses

1. Return *this by reference for chaining and for assignment operators (Module 4's operator= does exactly this).
2. Identity comparisons — this == &other answers "is it literally the same object?" (distinct from == meaning equal values).
3. Disambiguation — when a parameter shadows a member, this->name picks the member; better, rename instead.

In const member functions, this is const Account* — that is the whole mechanism by which const propagates to members.