using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        PhoneBook pb = new PhoneBook();

    }

}

​

public class PhoneBook 

{

     public PhoneBook()

    {

         GetAllContacts();

    }

    private List<Contact> _Contacts = new List<Contact>() {

        new Contact { MobileNumber = 09771400137, Name = "Nigel Anthony Olvieros" },

        new Contact { MobileNumber = 14143114, Name = "John Doe" },

        new Contact { MobileNumber = 431414123, Name = "Jay Col" },

    };

​

    public IEnumerable<Contact> Contacts { get { return this._Contacts; } }

    public void GetAllContacts()

    {

        foreach(Contact contact in _Contacts)

        {

            Console.WriteLine($"Name : {contact.Name } \n Number : {contact.MobileNumber} \n\n\n");

        }

    }

    public void AddContact (Contact contact)

    {

        _Contacts.Add(contact);

        Console.WriteLine($"{contact.Name} successfully added!");

    }

}

​

public class Contact: IContact

{

    public long MobileNumber {get;set;}

    public string Name {get;set;}

    public void Call() 

    {

        Console.WriteLine($"Calling {this.Name} ....");

    }

}

public interface IContact : IIntercom

{

    public long MobileNumber {get;set;}

​

}

public interface IIntercom

{

    void Call();

}