By now, you've got a handle on classes and vectors, but the real test is when you have to glue those concepts together to solve a problem. Today, we're building a text-based inventory management system. I've decided to model this after a small retro game shop—something simple, but it forces us to handle searching, updating, and displaying data effectively.

Defining what an "Item" actually is

I always start by sketching out the data. We don't need a massive class hierarchy here; a simple struct will do. We need a name, a quantity, and a price. Since we're dealing with money, I'll use double for the price, though in a professional financial app, you'd likely use integers representing cents to avoid floating-point errors. For this exercise, double is just fine.

struct Item {
    std::string name;
    int quantity;
    double price;
};

Handling the collection with a vector

I'm going with a std::vector<Item> because it's flexible. We don't know if the shop will have ten items or a thousand. I'll wrap the inventory logic in a class called InventoryManager. This keeps the main function clean and ensures the inventory data isn't just floating around globally, which is a habit you want to break early.

class InventoryManager {
private:
    std::vector<Item> items;

public:
    void addItem(const std::string& name, int qty, double price) {
        items.push_back({name, qty, price});
    }

    void displayInventory() const {
        for (const auto& item : items) {
            std::cout << item.name << " | Qty: " << item.quantity 
                      << " | Price: $" << item.price << "\n";
        }
    }
};

The "Search and Update" stumble

Now, here is where I usually trip up if I'm rushing. I wanted to add a function to update the quantity of an item. At first, I wrote it like this:

// DON'T DO THIS
void updateQuantity(std::string name, int newQty) {
    for (size_t i = 0; i < items.size(); ++i) {
        if (items[i].name == name) {
            items[i].quantity = newQty;
            return;
        }
    }
    // I forgot to handle the case where the item isn't found!
}

I realized that if the user tried to update a "GameBoy" that didn't exist in the list, the function would just silently exit. The user would think the update happened, but the data wouldn't change. It's a classic "silent failure." To fix this, I'll change the function to return a bool. That way, the calling code knows whether to show a success message or an error.

bool updateQuantity(const std::string& name, int newQty) {
    for (auto& item : items) {
        if (item.name == name) {
            item.quantity = newQty;
            return true;
        }
    }
    return false;
}

Wiring it into a user loop

Finally, we need a way to actually interact with this. I'll use a while loop and a switch statement. I prefer this over a series of if/else blocks because it's visually cleaner when you have more than two options. You'll notice I'm using std::getline for the item names—never use std::cin >> name if the name might contain a space (like "Super Mario Bros"), or you'll end up with a messy input buffer.

int main() {
    InventoryManager myShop;
    myShop.addItem("NES Console", 5, 99.99);
    myShop.addItem("Sega Genesis", 3, 79.99);

    int choice = 0;
    while (choice != 4) {
        std::cout << "\n1. View 2. Update 3. Add 4. Exit\nChoice: ";
        std::cin << choice;

        if (choice == 1) {
            myShop.displayInventory();
        } else if (choice == 2) {
            std::string name;
            int qty;
            std::cout << "Enter item name: ";
            std::cin.ignore(); // Clear the newline from the buffer
            std::getline(std::cin, name);
            std::cout << "Enter new quantity: ";
            std::cin << qty;
            
            if (myShop.updateQuantity(name, qty)) {
                std::cout << "Update successful!\n";
            } else {
                std::cout << "Item not found.\n";
            }
        }
        // ... other choices handled similarly
    }
    return 0;
}

📋 Practical Task

Exercise: Implementing a Low-Stock Warning Filter

Right now, the displayInventory method prints everything. In a real warehouse, you only care about what's running out. Your task is to modify the InventoryManager class to include a new method called displayLowStock(int threshold).

• This method should take an integer threshold as an argument.
• It should iterate through the inventory and only print items whose quantity is less than or equal to that threshold.
• If no items are low on stock, it should print a message saying "All stock levels are healthy."

Once you've written the method, add a new option to the main loop (Option 5) that asks the user for a threshold value and then calls this new function.