How can I iterate through all my vector elements and check their variables? (C++)

Question

So I have a problem with my C++ game. If I try to use an item that has the quantity <= than 0, it will work. How can I prevent the function from using the item if it's quantity is <= than 0? Here is some of the code:

Use item function

void Inventory::useItem(int id, int quantity, Character &character)
{
    if (id == 2 && !isNull())
    {
        removeQuantity(2, 1);
        cout << "\n" << "You used the item with Id 2!" << endl;
        character.addOrbs(100);
    }
    else
    {
        setColor(0x0C);
        cout << "\n" << "ERROR! ";
        setColor(0x07);
        cout << "There is no item with such ID!" << endl;
    }
}

Check if item quantity is 0 function

bool Inventory::isNull()
{
    for(auto &item : inventoryVec)
    {
        if (item.quantity <= 0)
            return true;
        else
            return false;
    }
}

Answer 1

Your isNull() method is checking if only the 1st item in the inventory, regardless of its id , has a quantity of <= 0 . It is ignoring all other items.

What you should be doing instead is looking specifically for the item with an id of 2, and then checking if that item has a quantity of <= 0 , eg:

bool Inventory::isNull(int id)
{
    for(auto &item : inventoryVec)
    {
        if (item.id == id)
            return (item.quantity <= 0);
    }
    return true;
}

void Inventory::useItem(int id, int quantity, Character &character)
{
    if ((id == 2) && !isNull(id))
    {
        removeQuantity(2, 1);
        cout << "\n" << "You used the item with Id 2!" << endl;
        character.addOrbs(100);
    }
    else
    {
        setColor(0x0C);
        cout << "\n" << "ERROR! ";
        setColor(0x07);
        cout << "There is no item with such ID!" << endl;
    }
}

Though, I would suggest changing useItem() to be more like this instead:

void Inventory::useItem(int id, int quantity, Character &character)
{
    if (!isNull(id))
    {
        removeQuantity(id, 1);
        cout << "\n" << "You used the item with Id " << id << "!" << endl;
        if (id == 2)
            character.addOrbs(100);
        else
            ... // handle other ids as needed...
    }
    else
    {
        setColor(0x0C);
        cout << "\n" << "ERROR! ";
        setColor(0x07);
        cout << "There is no item with such ID!" << endl;
    }
}