C# Online Compiler | .NET Fiddle

// product
public abstract class Card {}

// concrete product
public class BicycleCard : Card {}

// concrete product
public class BeeCard : Card {}

// creator
public abstract class CardPrinter
{
	// factory method
	protected abstract Card CreateCard();
	
	// operation
	public string PrintCard()
	{
		var card = CreateCard();
		return card.ToString();
	}
}

// concrete creator
public class BicycleCardPrinter : CardPrinter
{
	protected override Card CreateCard()
	{
		return new BicycleCard();
	}
}

// concrete creator
public class BeeCardPrinter : CardPrinter
{
	protected override Card CreateCard()
	{
		return new BeeCard();
	}
}

public class Program
{
	public static void Main()
	{
		RunClient(new BicycleCardPrinter());
		RunClient(new BeeCardPrinter());
	}
	
	
	// the client depends only on the `CardPrinter`
	private static void RunClient(CardPrinter cardPrinter)
	{
		System.Console.WriteLine("Doing work"); 

		var printedCard = cardPrinter.PrintCard();
		System.Console.WriteLine("- " + printedCard);
		System.Console.WriteLine("- " + printedCard);
	}
}

Compilation error (line 2, col 3): Preprocessor directive expected
Compilation error (line 3, col 3): Preprocessor directive expected
Compilation error (line 4, col 1): Preprocessor directive expected
Compilation error (line 5, col 3): Preprocessor directive expected
Compilation error (line 6, col 3): Preprocessor directive expected
Compilation error (line 8, col 17): ; expected
Compilation error (line 8, col 17): Syntax error, 'switch' expected
Compilation error (line 10, col 11): Syntax error, ':' expected
Compilation error (line 10, col 11): } expected
Compilation error (line 11, col 5): Too many characters in character literal
Compilation error (line 11, col 12): ; expected
Compilation error (line 11, col 12): } expected
Compilation error (line 12, col 11): Preprocessor directive expected
Compilation error (line 13, col 11): Preprocessor directive expected
Compilation error (line 14, col 11): Preprocessor directive expected
Compilation error (line 15, col 11): Preprocessor directive expected
Compilation error (line 16, col 12): ; expected
Compilation error (line 16, col 12): Unexpected character '$'
Compilation error (line 16, col 26): ; expected
Compilation error (line 18, col 20): Invalid expression term 'lock'
Compilation error (line 18, col 20): ; expected
Compilation error (line 18, col 24): Syntax error, '(' expected
Compilation error (line 18, col 24): Invalid expression term '/'
Compilation error (line 18, col 37): ) expected
Compilation error (line 20, col 5): Too many characters in character literal
Compilation error (line 20, col 11): ; expected
Compilation error (line 20, col 11): } expected
Compilation error (line 21, col 11): Preprocessor directive expected
Compilation error (line 22, col 11): Preprocessor directive expected
Compilation error (line 23, col 11): Preprocessor directive expected
Compilation error (line 24, col 12): ; expected
Compilation error (line 24, col 12): Unexpected character '$'
Compilation error (line 24, col 26): ; expected
Compilation error (line 24, col 110): ; expected
Compilation error (line 25, col 20): Invalid expression term 'lock'
Compilation error (line 25, col 20): ; expected
Compilation error (line 25, col 24): Syntax error, '(' expected
Compilation error (line 25, col 24): Invalid expression term '/'
Compilation error (line 25, col 37): ) expected
Compilation error (line 27, col 5): } expected