Increase count of item for a customer - c++

Question

Hello I do a shopping list. I have a class Customer and a class Item. My program work like this, I ask the name of the customer if the customer isn't in the database I add this customer, and if the customer is I print an error in order to say that the customer exists. After that I print a list of 10 products, and ask the customer to choose a product and increase the count of the specific Item for this customer.
My program don't give any error, I try do debug but I don't find the error, because the program doesn't increase the count of anything.
This is my function in my main:
void DisplayList(Item shopList[10], Customer& custom)
{
int choose_item = 1;
while (choose_item != 0)
{
cout << "The items you can buy are: (0 to exit)" << endl;
for (int i = 0; i < 10; i++)
{
cout << i + 1 << ". " << shopList[i].getName() << " " << shopList[i].getUnitPrice() << " x" << shopList[i].getCount() << endl;
}
cout << "What item you would like to buy, Input: ";
cin >> choose_item;
custom.addItem(shopList[choose_item - 1]);
}
}
My customer header:
class Customer
{
public:
Customer(string);
Customer(){}
void addItem(Item);
set<Item> getItems() const;
private:
string _name;
set<Item> _items;
};
My customer cpp
Customer::Customer(string name)
{
_name = name;
}
Customer::Customer(){ };
void Customer::addItem(Item SpecificItem)
{
set<Item>::iterator it;
if ((it = _items.find(SpecificItem)) != _items.end())
{
SpecificItem.setCount(SpecificItem.getCount() + 1);
}
else
{
_items.insert(SpecificItem);
}
}
set<Item> Customer::getItems() const
{
return _items;
}
My item header:
class Item
{
public:
Item(string, string, double);
~Item();
//get and set functions
string getName() const;
string getSerialNumber() const;
int getCount();
double getUnitPrice() const;
void setCount(int count);
private:
string _name;
string _serialNumber; //consists of 5 numbers
int _count; //default is 1, can never be less than 1!
double _unitPrice; //always bigger than 0!
};
My item cpp
#include "Item.h"
Item::Item(string name, string serial_number, double price) : _name(name), _serialNumber(serial_number), _unitPrice(price), _count(1)
{
};
Item::~Item(){};
string Item::getName() const
{
return _name;
}
string Item::getSerialNumber() const
{
return _serialNumber;
}
int Item::getCount()
{
return _count;
}
double Item::getUnitPrice() const
{
return _unitPrice;
}
void Item::setCount(int count)
{
_count = count;
}