Throughout this book, we will work with C# 6.0 (introduced in Microsoft Visual Studio 2015). However, most of the explanations and code samples are also compatible with C# 5.0 (introduced in Visual Studio 2013). If a specific example uses C# 6.0 syntax and isn't compatible with C# 5.0, the code will be properly labeled with the compatibility warning. We will use Visual Studio Community 2015 as the main IDE. However, you can also run the examples using Mono or Xamarin.

The following lines declare a new minimal Circle class in C#:

class Circle
{
}

The class keyword followed by the class name (Circle) composes the header of the class definition. In this case, the class doesn't have a parent class or a superclass. Therefore, there aren't any superclasses listed after the class name and a colon (:). A pair of curly braces ({}) encloses the class body after the class header. In this case, the class body is empty. The Circle class is the simplest possible class we can declare...