using System;

namespace Example57
{
	class Person
	{
		private string idNumber;
		private string lastName;
		private string firstName;
		private int age;

		public Person()
		{
			idNumber = "";
			lastName = "unknown";
			firstName = "unknown";
			age = 0;
		}

		public Person(string idNumber, string lastName, string firstName,
			int age)
		{
			this.idNumber = idNumber;
			this.lastName = lastName;
			this.firstName = firstName;
			this.age = age;
		}

		public Person(string idNumber, string lastName, string firstName) : 
			this(idNumber, lastName, firstName, 0)
		{
		}

		public Person(string idNumber) : this(idNumber, "unknown", "unknown")
		{
		}
	}

	class Student : Person
	{
		private string major;
		private string studentID;

		public Student() : base()
		{
			major = "unknown";
			studentID = "";
		}

		public Student(string personID, string firstName, string lastName,
			string major, string studentID) : base(personID, firstName, 
			lastName)
		{
			this.major = major;
			this.studentID = studentID;
		}
	}
	/// <summary>
	/// Summary description for Class1.
	/// </summary>
	class Class1
	{
		/// <summary>
		/// The main entry point for the application.
		/// </summary>
		[STAThread]
		static void Main(string[] args)
		{
			Person p = new Person();
			Student s = new Student("22", "Rex", "xyz", "Computer Science",
				"333");
		}
	}
}