Interface, Base, Chained Constructor, Properties, Init, Events, Methods, et al.

ClassSample.cs

public interface IAccount
{
	int Balance { get; }

	void Deposit(int amount);
	void Withdraw(int amount);

	event EventHandler<int> BalanceChanged;
	event EventHandler<int> Overdraft;
}

public abstract class Account : IAccount
{
	private int balance = 0;
	public int Balance 
	{ 
		get => balance; 
		private set 
		{ 
			BalanceChanged?.Invoke(this, (balance = value));
			if (value < 0) Overdraft?.Invoke(this, value);
		}
	}

	public void Deposit(int amount) => Balance += Math.Abs(amount);
	public void Withdraw(int amount) => Balance -= Math.Abs(amount);

	public event EventHandler<int> BalanceChanged;
	public event EventHandler<int> Overdraft;
}

public class SavingsAccount : Account
{
	public SavingsAccount(int number) => AccountNumber = number;

	public SavingsAccount(int number, string name)
		: this(number) => AccountName = name;

	public int AccountNumber { get; } = default;
	
	public string AccountName { get; init; } = "No Name Provided";
}

var savings = new SavingsAccount(8675309)
{
	AccountName = "Jerry Nixon",
};

savings.BalanceChanged += HandleBalanceChanged;
savings.Overdraft += HandleOverdraft;

savings.Deposit(100);
savings.Deposit(200);
savings.Withdraw(300);
savings.Withdraw(10);

void HandleBalanceChanged(object sender, int balance)
{
	Console.WriteLine($"New balance is {balance:C0}");
}

void HandleOverdraft(object sender, int balance)
{
	Console.WriteLine($"Invalid balance: {balance:C0}");
}