Описание структуры

#include <vector>
#include <iostream>
#include <string>
#include <algorithm>
 
using namespace std;
 
enum class options {brand,year,price};
 
 
 
struct Car
{
    string brand;
    string colour;
    int year;
    int price;
 
    bool operator<(Car& c)const  //For sort from <algorithm>
    {
        return year < c.year;
    }
 
    
};
 
void Print(vector<Car>&, options opt);
istream& operator>>(istream&, Car&); //INPUT
ostream& operator<<(ostream&, Car);  //OUTPUT
 
 
istream& operator>>(istream& is, Car& c)
{
    cout << "Brand: ";
    cin >> c.brand;
    cout << "Colour: ";
    cin >> c.colour;
    cout << "Year: ";
    cin >> c.year;
    cout << "Price: ";
    cin >> c.price;
    cout << endl;
    return is;
}
 
ostream& operator<<(ostream& os, Car c)
{
    os << c.brand << ", " << c.colour << ", " << c.year << ", " << c.price << "$.";
    return os;
}
 
 
void Print(vector<Car>& vec, options opt)
{
    int from, to, year;
    string brand;
    
    switch (opt)
    {
    case options::brand:
        cout << "Brand: ";
        cin >> brand;
        break;
    case options::year:
        cout << "Year: ";
        cin >> year;
        break;
    case options::price:
        cout << "From: ";
        cin >> from;
        cout << "To: ";
        cin >> to;
        break;
    }
    
    for (Car c : vec)
    {
        switch (opt)
        {
        case options::brand:
            if (c.brand == brand) cout << c<<endl;
            break;
        case options::year:
            if (c.year == year) cout << c<<endl;
            break;
        case options::price:
            if (c.price >= from && c.price <= to) cout << c<<endl;
            break;
        }
    }
}
 
int main()
{
    int n;
    vector<Car> vec;
    cout << "Please Enter a number of cars: ";
    cin >> n;
    cout << endl;
    for (int i = 0; i < n;i++)
    {
        cout << "Car #" << i+1 << endl;
        Car c;
        cin >> c;
        vec.push_back(c);
    }
 
    sort(vec.begin(), vec.end());
 
    Print(vec, options::brand);
    Print(vec, options::year);
    Print(vec, options::price);
    system("pause");
}