simple Friends program

[Billyin4C]

Why am I not getting any output for Customer Number, City, State, and Zip code?

  #include<iostream>
#include <string>
using namespace std;


class City;
class Customer
{
private:
	int customerNumber;
	int zipcode;
public:
	Customer(int number, int zip)
	{
		customerNumber = number;
		zipcode = zip;
	}
	friend void display(Customer customer, City city);
};
class City
{
private:
	string city;
	string state;
public:
	City(string C, string S)
	{
		city = C;
		state = S;
	}

	
	friend void display(Customer customer, City city);

};

void display(Customer customer, City city)
{
	cout << "Customer Number: " << endl;
	cout << "City: " << endl;
	cout << "State: " << endl;
	cout << "Zip code: " << endl;
}

int main()
{
	Customer customer(1234, 28054);
	City city("Gastonia", "North Carolina");
	display(customer, city);
	
	return 0;
}

[ne555]

your program produces this output

Customer Number: 
City: 
State: 
Zip code: 

¿were you expecting anything else?

the compiler cannot read minds.