Composition

using System;

class Address
{
    public string City;

    public Address(string city)
    {
        City = city;
    }
}

class Customer
{
    public string Name;
    public Address Address;

    public Customer(string name, Address address)
    {
        Name = name;
        Address = address;
    }
}

class Program
{
    static void Main()
    {
        string city = "Oslo""Cairo""Lima";
        Address address = new Address(city);
        Customer customer = new Customer("Mira", address);
        string summary = customer.Name + "@" + customer.Address.City;

        Console.WriteLine($"city={city}");
        Console.WriteLine($"summary={summary}");
    }
}

using System;

class Address
{
    public string City;

    public Address(string city)
    {
        City = city;
    }
}

class Customer
{
    public string Name;
    public Address Address;

    public Customer(string name, Address address)
    {
        Name = name;
        Address = address;
    }
}

class Program
{
    static void Main()
    {
        string city = "Oslo""Cairo""Lima";
        Address address = new Address(city);
        Customer customer = new Customer("Mira", address);
        string summary = customer.Name + "@" + customer.Address.City;

        Console.WriteLine($"city={city}");
        Console.WriteLine($"summary={summary}");
    }
}

using System;

class Address
{
    public string City;

    public Address(string city)
    {
        City = city;
    }
}

class Customer
{
    public string Name;
    public Address Address;

    public Customer(string name, Address address)
    {
        Name = name;
        Address = address;
    }
}

class Program
{
    static void Main()
    {
        string city = "Oslo""Cairo""Lima";
        Address address = new Address(city);
        Customer customer = new Customer("Mira", address);
        string summary = customer.Name + "@" + customer.Address.City;

        Console.WriteLine($"city={city}");
        Console.WriteLine($"summary={summary}");
    }
}