Refactor Incomplete Classes

Rockstar's gameplay tools team left this inventory system half-finished: two classes, with two of the methods unimplemented, plus a few real problems in the parts that were written.

class InventorySlot {
public:
    InventorySlot(int itemId, int quantity) : itemId_(itemId), quantity_(quantity) {}

    int getItemId() const { return itemId_; }
    int getQuantity() const { return quantity_; }

    void addQuantity(int amount) {
        quantity_ += amount;
    }

private:
    int itemId_;
    int quantity_;
};

class PlayerInventory {
public:
    PlayerInventory(int capacity) : capacity_(capacity) {
        slots_ = new InventorySlot*[capacity_];
        for (int i = 0; i < capacity_; i++) {
            slots_[i] = nullptr;
        }
    }

    bool addItem(int itemId, int quantity) {
        // method body intentionally left unfinished for this exercise
        return false;
    }

    int totalItems() {
        // method body intentionally left unfinished for this exercise
        return 0;
    }

    InventorySlot* getSlot(int index) {
        return slots_[index];
    }

private:
    InventorySlot** slots_;
    int capacity_;
};

Write real implementations for addItem (add to an existing slot for that item, or use the first empty slot if there isn't one) and totalItems (sum the quantity across all occupied slots). Then explain the other problems in PlayerInventory as written, and describe how you would fix each one.