C# 4.0 : Add a Static Constructor and Initialization

Static fields can be initialized in two ways. One way is with a static constructor, which is similar to a standard constructor, but with no accessibility modifier or arguments:

public class Vertex3d
{
    private static int _numInstances;
    static Vertex3d()
    {
        _numInstances = 0;
    }
    ...
}

However, because of performance reasons, it is preferable to initialize static fields inline whenever possible, as shown here:

public class Vertex3d
{
    private static int _numInstances = 0;
    ...
}