Copying a specific field from a vector into another vector - c++

Question

I am trying to make a basket system for a C++ program, and I am stuck with the task of obtaining the price from one vector in a separate class, and copying that price into the new "Basket" Vector. i have tried a number of workaround but I have gotten as far as having it return the error message that the identifier is undefined, even though the vector is public in the class.
the header file :
class Item {
private:
int _ItemNo;
string _category, _description;
double _price;
double _VAT = _price*0.2;
double _subtotal = _price + _VAT;
};
class ItemMenu {
public:
vector<Item> _Items;
ItemMenu();
void displayMenu();
};
//Class for ordering from the menu
class Ordering {
private:
vector<Item> _Basket;
int quantity;
double total;
public:
Ordering();
Ordering(int quantity, double total);
void placeOrder(const vector<Item> &Items);
The implementation file:
ItemMenu::ItemMenu() {
ifstream fin("Menu.txt");
if(fin) {
while(!fin.eof()) {
string _ItemNoTemp;
getline(fin, _ItemNoTemp, ':');
int _ItemNo = stoi(_ItemNoTemp);
string _category;
getline(fin, _category, ':');
string _description;
getline(fin, _description, ':');
string _priceTemp;
getline(fin, _priceTemp);
double _price = stod(_priceTemp);
if(!fin.eof()) {
_Items.push_back(Item(_ItemNo,
_category, _description, _price));
};
fin.peek();
}
fin.close();
}
}
//Method to display the each item
void ItemMenu::displayMenu() {
for(int i = 0; i < _Items.size(); ++i) {
_Items[i].display();
}
cout << endl;
}
Ordering::Ordering() { }
void Ordering::placeOrder() {
int select;
cout << "Please enter an item number: ";
cin >> select;
Item I;
i._subtotal = _Items[select]._subtotal;
_Basket.push_back(i);
}
It is in the ordering class that the basket vector is in, and I am trying to get the subtotal for the items, so that I may calculate the total by summing the values in the vector. This is also where the error saying that _Items is undefined appeared. I am new to programing and haven't really been able to find a clear source for how vectors work between classes depending on where they are declared.

Answer 1

Something like this should work
void Ordering::placeOrder(
const vector<Item>& items ) {
int select;
cout << "Please enter an item number: ";
cin >> select;
cItem i;
i._price = items[ select ]._price;
_Basket.push_back( i );
}

Answer 2

You don't actually pass an ItemMenu object to this function. That's why you are getting an undefined error.
Instead of this
void Ordering::placeOrder() {
int select;
cout << "Please enter an item number: ";
cin >> select;
_Basket.push_back(_Items[select]._subtotal);
}
You would want to do this
void Ordering::placeOrder(ItemMenu yourItemMenuVarible) {
int select;
cout << "Please enter an item number: ";
cin >> select;
_Basket.push_back(_Items[select]._subtotal);
}
then when you call it you would pass it the ItemMenu variable you defined and I think that should fix it.
I would also recommend you not have variables like the vector public, it not a very good practice for security reasons. Learning good habits now will help you in the future. The idea of keeping them private is called Encapsulation here are some sources on the topic
https://www.geeksforgeeks.org/encapsulation-in-c/
https://www.tutorialspoint.com/cplusplus/cpp_data_encapsulation.htm#:~:text=Encapsulation%20is%20an%20Object%20Oriented,from%20outside%20interference%20and%20misuse.&text=This%20means%20that%20they%20can,other%20part%20of%20your%20program.

Answer 3

Thanks for all the help guys i ended up fixing it with your help the code is below.
Header File:
class Ordering {
private:
vector<Item> _Basket;
int quantity;
double total;
public:
Ordering();
Ordering(int quantity, double total);
void placeOrder(vector<Item> Items);
};
Implementation:
Ordering::Ordering() { }
void Ordering::placeOrder(vector<Item> _Items) {
int select;
Item i;
char cont;
do{
cout << "Please enter an item number: ";
cin >> select;
i._ItemNo = _Items[select-1]._ItemNo;
i._description = _Items[select-1]._description;
i._subtotal = _Items[select-1]._subtotal;
_Basket.push_back(i);
cout << i._subtotal;
cout << "Do you want to add another Item? (y/n): ";
cin >> cont;
}while(cont == 'y' || cont == 'Y');
for (int i; i < _Basket.size(); i++) {
cout << _Basket[i]._ItemNo << ':' << _Basket[i]._description
<< ':' << char(156) << _Basket[i]._subtotal << endl;
};
}
Main:
int main() {
cout << "--------------------------------" << endl;
cout << "Billing Program" << endl <<
"--------------------------------" << endl;
Ordering start;
ItemMenu display;
display.displayMenu();
start.placeOrder(display._Items);
}