Protected Members

A protected member is visible inside the class and its derived classes.

ProtectedMembers.cs

using System;

class Account
{
    protected int balance;

    public Account(int openingBalance)
    {
        balance = openingBalance;
    }
}

class SavingsAccount : Account
{
    public SavingsAccount(int openingBalance) : base(openingBalance)
    {
    }

    public void AddInterest(int amount)
    {
        balance += amount;
    }

    public int Balance
    {
        get { return balance; }
    }
}

class Program
{
    static void Main()
    {
        int interest = ;
        SavingsAccount account = new SavingsAccount(20);
        account.AddInterest(interest);

        Console.WriteLine($"interest={interest}");
        Console.WriteLine($"balance={account.Balance}");
    }
}

using System;

class Account
{
    protected int balance;

    public Account(int openingBalance)
    {
        balance = openingBalance;
    }
}

class SavingsAccount : Account
{
    public SavingsAccount(int openingBalance) : base(openingBalance)
    {
    }

    public void AddInterest(int amount)
    {
        balance += amount;
    }

    public int Balance
    {
        get { return balance; }
    }
}

class Program
{
    static void Main()
    {
        int interest = ;
        SavingsAccount account = new SavingsAccount(20);
        account.AddInterest(interest);

        Console.WriteLine($"interest={interest}");
        Console.WriteLine($"balance={account.Balance}");
    }
}

using System;

class Account
{
    protected int balance;

    public Account(int openingBalance)
    {
        balance = openingBalance;
    }
}

class SavingsAccount : Account
{
    public SavingsAccount(int openingBalance) : base(openingBalance)
    {
    }

    public void AddInterest(int amount)
    {
        balance += amount;
    }

    public int Balance
    {
        get { return balance; }
    }
}

class Program
{
    static void Main()
    {
        int interest = ;
        SavingsAccount account = new SavingsAccount(20);
        account.AddInterest(interest);

        Console.WriteLine($"interest={interest}");
        Console.WriteLine($"balance={account.Balance}");
    }
}

protected Protected members share state with derived classes without making it public.