C++ OOP 类和构造函数

Question

Pretty new to C++ here and programming as a whole so please be patient and understanding that my explanations may not be on the mark. The assignment for my OOP class calls for the following:

Design an Inventory class that can hold information for an item in a retail store's inventory. Required private member variables: - item number - quantity - cost Required public member functions

Default constructor - Sets all the member variables to 0 Constructor #2 - Accepts an item's number, quantity and cost as arguments. Calls other class functions to copy these values into the appropriate member variables.

They way I'm going about this is slightly different. Rather than 1 value I'm trying to initialize an array and store all the values enter by the user there. However it seems, once the user exits the member/class function the value is removed from the array.

Kind of at my wits end here so any info or recommendations would greatly help.

#include <iostream>
using namespace std;

class inventory
{
    private:
        int productNum[10];
        int productCount[10];
        double productPrice[10];
        int inventoryFillLevel;
        int userPNumber;
        int userQuantity;
        double userPrice;
    public:
        inventory()
        {
            int counter = 0;
            userPNumber = 0;
            userQuantity = 0;
            userPrice = 0;
            while (counter < 10)
            {
                productNum[counter] = 5;
                productCount[counter] = 6;
                productPrice[counter] = 7;
                counter++;
            }
        }
        inventory(int pNumber, int pCount, int pPrice)
        {
            cout << "Now we're in the 2nd constructor in the Class" << endl;
            cout << "The 1st number entered by the user is: " << pNumber << endl;
            cout << "The 2nd number entered by the user is: " << pCount << endl;
            cout << "The 3rd number entered by the user is: " << pPrice << endl;
            Input(pNumber);
        }
        void Input(int pNumber)
        {
            int counter = 0;
            cout << "\nNow we're in the function as called by the Constructor." << endl;
            cout << "The 1st number entered by the user is: " << pNumber << endl;
            cout << "In the function the counter is: " << counter << endl;
            cout << "The value in the array at " << counter << " is: " << productNum[counter] << endl;
            cout << "Now we set that to the value entered by the user" << endl;
            productNum[counter] = pNumber;
            cout << "And now the value in the array is: " << productNum[counter] << endl;
        }
         void Show()
        {
            int counter = 0;
            cout << "After entering the value, let's check what is stored in the array: ";
            cout << productNum[counter] << endl;
        }
};

 int main()
{

    int a=0;
    int b=0;
    int c=0;

    inventory inv1;

    cout << "1st User entered value" << endl;
    cin >> a;
    cout << "2nd User entered value" << endl;
    cin >> b;
    cout << "3rd User entered value" << endl;
    cin >> c;

    cout << "Now we call the 2nd constructor and pass the values to it" << endl;
    inventory(a, b, c);

    inv1.Show();    

    return 0;

}

Thanks again for any help with this.

Answer 1

You appear to be handling your class incorrectly. The line

inventory(a, b, c);

only creates a temporary instance of inventory that is gone essentially after the line finishes execution. So when you call inv1.Show() it's still using the values that are assigned in your default constructor when inv1 was declared. You should remove the current declaration of inv and change

inventory(a, b, c);

to

inventory inv1(a, b, c);

Answer 2

Value are not getting removed. There is small flaw in the code.

1)- You are making mistake while creating an object. You are calling Show method with object created by default constructor.

inventory inv1;

....
inv1.Show();

Change the declaration of inv1 to inventory inv1(a, b, c); and call then call show method.

Also inventory(a, b, c); will create new object and will not effect inv1 .

2)- You are always storing values at index 0 of the member array. As you are declaring int counter = 0 whenever you are calling any method/constructor.

Make int counter ; a class member.

class inventory
{
    private:
        int counter;
    public:
       inventory():counter(0){....}

    ....
};

It will count the items you already push in your inventory. Though you will have to take care how many item you already pushed in. Alternative approach can be you can use std::vector instead of int array .