Question

I am doing a homework assignment for my summer OO class and we need to write two classes. One is called Sale and the other is called Register. I’ve written my Sale class; here’s the .h file:

enum ItemType {BOOK, DVD, SOFTWARE, CREDIT};

class Sale
{
public:
    Sale();         // default constructor, 
            // sets numerical member data to 0

    void MakeSale(ItemType x, double amt);  

    ItemType Item();        // Returns the type of item in the sale
    double Price();     // Returns the price of the sale
    double Tax();       // Returns the amount of tax on the sale
    double Total();     // Returns the total price of the sale
    void Display();     // outputs sale info 

private:
    double price;   // price of item or amount of credit
    double tax;     // amount of sales tax 
    double total;   // final price once tax is added in.
    ItemType item;  // transaction type
};

For the Register class we need to include a dynamic array of Sale objects in our member data.

So my two questions are:

• Do I need to inherit from my Sale class into my Register class (and if so, how)?
• Can I have a generic example of a dynamic array?

Edit: We cannot use vectors.

Answer 1

No, inheritance would not be appropriate in this case. You would want to keep track of the number of sales and the size of the array as fields in the Register class. The class definition would include this

class Register{
    private:
        int numSales;
        int arraySize;
        Sale* sales;
    public:
        Register();
        ~Register();
        void MakeSale(Sale);        
};

Register::Register(){
    numSales = 0;
    arraySize = 5;
    sales = new Sale[arraySize];
}
void Register::MakeSale(Sale s){
    if(numSales == arraySize){
        arraySize += 5;
        Sale * tempArray = new Sale[arraySize];
        memcpy(tempArray, sales, numSales * sizeof(Sale));
        delete [] sales;
        sales = tempArray;
    }
    sales[numSales] = s;
    ++numSales;
}

Register::~Register()
{
    delete [] sales;
}

This doesn’t include bounds checking or whatever other stuff you need to do when you make a sale, but hopefully this should help.