• two kinds of types: value types and reference types;
• value types include primitive types whose sizes are not platform-dependent;
• reference types include class types, interface types and array types.

• classes are organized into a class hierarchy;
• root class is System.Object;
• single inheritance;
• a class may implement one or more interfaces;
• an abstract class may represent common aspects;
• a class can provide constructors;
• overriding is possible;
• you can control the visibility of a class and its members.

• in C#, there are no global functions or global variables;
• an exception can be represented using a class derived from System.Exception;
• an exception can be thrown using a throws statement;
• an exception can be handled using a try statement.

namespace First
{
    public class Point
    {
        private int iX;
        private int iY;
        public Point(int pX, int pY)
        {
            iX = pX;
            iY = pY;
        }
        public override string ToString()
        {
            return iX + ":" + iY;
        }
    }
}

using System;
namespace First
{
    public class PointTest
    {
        public static void Main()
        {
            Point tPoint = new Point(100, 200);
            Console.WriteLine(tPoint);
            Point tAnotherPoint = tPoint;
            Console.WriteLine(tAnotherPoint);
        }
    }
}

namespace First
{
    public class NamedPoint : Point
    {
        private string iName;
        public NamedPoint(string pName, int pX, int pY)
            : base(pX, pY)
        {
            iName = pName;
        }
        public override string ToString()
        {
            return iName + "%" + base.ToString();
        }
    }
}

using System;
namespace First
{
    public class NamedPointTest
    {
        public static void Main()
        {
            NamedPoint tNamedPoint = new NamedPoint("first", 100, 200);
            Console.WriteLine(tNamedPoint);
            Point tPoint = tNamedPoint;
            Console.WriteLine(tPoint);
        }
    }
}

Public Class Point
    Private iX As Integer
    Private iY As Integer
    Public Sub New(ByVal pX As Integer, ByVal pY As Integer)
        iX = pX
        iY = pY
    End Sub
    Public Overrides Function ToString() As String
        Return iX & ":" & iY
    End Function
End Class

Module PointTest
    Sub Main()
        Dim tPoint As Point = New Point(100, 200)
        Console.WriteLine(tPoint)
        Dim tAnotherPoint As Point = tPoint
        Console.WriteLine(tAnotherPoint)
    End Sub
End Module

Public Class NamedPoint
    Inherits Point
    Private iName As String
    Public Sub New(ByVal pName As String, ByVal pX As Integer, ByVal pY As Integer)
        MyBase.New(pX, pY)
        iName = pName
    End Sub
    Public Overrides Function ToString() As String
        Return iName & "%" & MyBase.ToString()
    End Function
End Class

Module NamedPointTest
    Sub Main()
        Dim tNamedPoint As NamedPoint = New NamedPoint("first", 100, 200)
        Console.WriteLine(tNamedPoint)
        Dim tPoint As Point = tNamedPoint
        Console.WriteLine(tPoint)
    End Sub
End Module

We have now provided 4 classes in both C# and VB.NET:

• Point
• PointTest
• NamedPoint
• NamedPointTest

We can mix the languages, e.g., use C#'s NamedPointTest class with VB.NET's NamedPoint class and C#'s Point class.