public class Person
{
    // Field
    public string name;

    // Constructor that takes no arguments.
    public Person()
    {
        name = "unknown";
    }

    // Constructor that takes one argument.
    public Person(string nm)
    {
        name = nm;
    }

    // Method
    public void SetName(string newName)
    {
        name = newName;
    }
}
class TestPerson
{
    static void Main()
    {
        // Call the constructor that has no parameters.
        Person person1 = new Person();
        Console.WriteLine(person1.name);

        person1.SetName("John Smith");
        Console.WriteLine(person1.name);

        // Call the constructor that has one parameter.
        Person person2 = new Person("Sarah Jones");
        Console.WriteLine(person2.name);

        // Keep the console window open in debug mode.
        Console.WriteLine("Press any key to exit.");
        Console.ReadKey();
    }
}
// Output:
// unknown
// John Smith
// Sarah Jones