Csharp/C Sharp/Class Interface/Class Definition

A program that uses the Building class

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
// A program that uses the Building class.   
 
using System;  
  
class Building {   
  public int floors;    // number of floors 
  public int area;      // total square footage of building 
  public int occupants; // number of occupants 
}   
   
// This class declares an object of type Building.   
public class BuildingDemo {   
  public static void Main() {   
    Building house = new Building(); // create a Building object 
    int areaPP; // area per person 
   
    // assign values to fields in house 
    house.occupants = 4;  
    house.area = 2500;  
    house.floors = 2;  
   
    // compute the area per person 
    areaPP = house.area / house.occupants;  
   
    Console.WriteLine("house has:\n  " + 
                      house.floors + " floors\n  " + 
                      house.occupants + " occupants\n  " + 
                      house.area + " total area\n  " + 
                      areaPP + " area per person"); 
  }   
}

A Simple C# Class

using System;
public class ASimpleClass
{
    public static void Main()
    {
        Point myPoint = new Point(10, 15);
        Console.WriteLine("myPoint.x {0}", myPoint.x);
        Console.WriteLine("myPoint.y {0}", myPoint.y);
    }
}
class Point
{
    // constructor
    public Point(int x, int y)
    {
        this.x = x;
        this.y = y;
    }
    
    // member fields
    public int x;
    public int y;
}

A simple inventory example

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
// A simple inventory example. 
 
using System; 
using System.Collections; 
 
class Inventory { 
  string name; 
  double cost; 
  int onhand; 
 
  public Inventory(string n, double c, int h) { 
    name = n; 
    cost = c; 
    onhand = h; 
  } 
 
  public override string ToString() { 
    return 
      String.Format("{0,-10}Cost: {1,6:C}  On hand: {2}", 
                    name, cost, onhand); 
  } 
} 
 
public class InventoryList { 
  public static void Main() { 
    ArrayList inv = new ArrayList(); 
     
    // Add elements to the list 
    inv.Add(new Inventory("Pliers", 5.95, 3)); 
    inv.Add(new Inventory("Wrenches", 8.29, 2));    
    inv.Add(new Inventory("Hammers", 3.50, 4)); 
    inv.Add(new Inventory("Drills", 19.88, 8)); 
 
    Console.WriteLine("Inventory list:"); 
    foreach(Inventory i in inv) { 
      Console.WriteLine("   " + i); 
    } 
  } 
}

Assign value to class

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/

// This program will not compile. 
 
class X { 
  int a; 
 
  public X(int i) { a = i; } 
} 
 
class Y { 
  int a; 
 
  public Y(int i) { a = i; } 
} 
 
public class IncompatibleRef { 
  public static void Main() { 
    X x = new X(10); 
    X x2;  
    Y y = new Y(5); 
 
    x2 = x; // OK, both of same type 
 
    x2 = y; // Error, not of same type 
  } 
}

Create class

/*
Learning C# 
by Jesse Liberty
Publisher: O"Reilly 
ISBN: 0596003765
*/
 using System;
 public class MyTime
 {
     // private variables
     private int year;
     private int month;
     private int date;
     private int hour;
     private int minute;
     private int second;
     // public methods
     public void DisplayCurrentMyTime()
     {
         Console.WriteLine(
             "stub for DisplayCurrentMyTime");
     }
 }
 public class Tester
 {
     static void Main()
     {
         MyTime timeObject = new MyTime();
         timeObject.DisplayCurrentMyTime();
     }
 }

Declare class and use it

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
using System; 
 
class Rect { 
  public int width; 
  public int height; 
 
  public Rect(int w, int h) { 
    width = w; 
    height = h; 
  } 
 
  public int area() { 
    return width * height; 
  } 
} 
  
public class UseRect { 
  public static void Main() {   
    Rect r1 = new Rect(4, 5); 
    Rect r2 = new Rect(7, 9); 
 
    Console.WriteLine("Area of r1: " + r1.area()); 
 
    Console.WriteLine("Area of r2: " + r2.area()); 
 
  } 
}

Declaring and Defining Classes

/*
 * C# Programmers Pocket Consultant
 * Author: Gregory S. MacBeth
 * Email: gmacbeth@comporium.net
 * Create Date: June 27, 2003
 * Last Modified Date:
 */
using System;
namespace Client.Chapter_5___Building_Your_Own_Classes
{
  public class DeclaringandDefiningClasses
  {
    static private int MyInt = 5;
    static public int MyInt2 = 10;
    static public int[] MyIntArray;
    static private int ObjectCount = 0;
    static void Main(string[] args)
    {
      MyIntArray = new int[10];
      ObjectCount++;
    }
    public static int MyMethod(int myInt)
    {
      MyInt = MyInt + myInt;
      return MyInt;
    }
    private static long MyLongMethod(ref int myInt)
    {
      return myInt;
    }
  }
}

Declaring Class Instances

/*
 * C# Programmers Pocket Consultant
 * Author: Gregory S. MacBeth
 * Email: gmacbeth@comporium.net
 * Create Date: June 27, 2003
 * Last Modified Date:
 */
using System;
namespace Client.Chapter_5___Building_Your_Own_Classes
{
  public class DeclaringClassInstances
  {
    static void Main(string[] args)
    {
      ClassInstantied MyClass = new ClassInstantied();
    }
  }
  class ClassInstantied
  {
    public void Display()
    {
      Console.WriteLine("Hello World");
    }
  }
}

Demonstrate the use of a nested class to contain data

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa
Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/
//
// Nested.cs -- demonstrate the use of a nested class to contain data
//
//              Compile this program with the following command line
//                  C:>csc Nested.cs
//
namespace nsReadOnly
{
    using System;
    
    public class Nested
    {
        static double DegreeFactor = 1;
        static double MilFactor = 0.05625;
        static double RadianFactor = 57.29578;
        static public void Main ()
        {
            double angle = 90;
            double radius = 50;
            
            // Declare an instance of the nested class
            clsArea.clsData data = new clsArea.clsData (angle, radius,
                                                        DegreeFactor);
            clsArea InDegrees = new clsArea (data);
            // Change the values to mils
            data.Factor = MilFactor;
            data.Angle = angle * 17.77778;
            clsArea InMils = new clsArea (data);
            // Change the values to radians
            data.Angle = angle / 57.29578;
            data.Factor = RadianFactor;
            clsArea InRadians = new clsArea (data);
            Console.WriteLine ("Area of pie of {0,0:F3} degrees is {1,0:F1}",
                               InDegrees.Data.Angle, InDegrees.Area);
            Console.WriteLine ("Area of pie of {0,0:F3} radians is {1,0:F1}",
                               InRadians.Data.Angle, InRadians.Area);
            Console.WriteLine ("Area of pie of {0,0:F3} mils is {1,0:F1}",
                               InMils.Data.Angle, InMils.Area);
        }
    }
    class clsArea
    {
        public class clsData : ICloneable
        {
            public clsData (double angle, double radius, double factor)
            {
                m_Angle = angle;
                m_Radius = radius;
                m_Factor = factor / 57.29578;
            }
            public double Angle
            {
                get {return(m_Angle);}
                set {m_Angle = value;}
            }
            public double Radius
            {
                get {return(m_Radius);}
                set {m_Radius = value;}
            }
            public double Factor
            {
                get {return(m_Factor);}
                set {m_Factor = value / 57.29578;}
            }
            private double m_Angle = 0;
            private double m_Radius = 0;
            private double m_Factor = 1;
            public object Clone ()
            {
                clsData clone = new clsData (m_Angle, m_Radius,
                                             m_Factor * 57.29578);
                return (clone);
            }
        }
        public clsArea (clsData data)
        {
            // Clone the data object to get a copy for ourselves
            m_Data = (clsData) data.Clone();
        }
        public clsData Data
        {
            get {return (m_Data);}
        }
        private clsData m_Data;
        private const double pi = 3.14159;
        private const double radian = 57.29578;
        public double Area
        {
            get
            {
               return (m_Data.Radius * m_Data.Radius * pi
                       * m_Data.Angle * m_Data.Factor /  (2 * pi));
            }
        }
    }
}

Illustrates hiding

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy
Publisher: Sybex;
ISBN: 0782129110
*/
/*
  Example5_4.cs illustrates hiding
*/

// declare the Car class
class Car
{
  public int yearBuilt;
  public double maximumSpeed;
  public int Age(int currentYear)
  {
    int maximumSpeed = 100;  // hides the field
    System.Console.WriteLine("In Age(): maximumSpeed = " +
      maximumSpeed);
    int age = currentYear - yearBuilt;
    return age;
  }
  public double Distance(double initialSpeed, double time)
  {
    System.Console.WriteLine("In Distance(): maximumSpeed = " +
      maximumSpeed);
    return (initialSpeed + maximumSpeed) / 2 * time;
  }
}

public class Example5_4
{
  public static void Main()
  {
    // create a Car object
    Car redPorsche = new Car();
    redPorsche.yearBuilt = 2000;
    redPorsche.maximumSpeed = 150;
    int age = redPorsche.Age(2001);
    System.Console.WriteLine("redPorsche is " + age + " year old.");
    System.Console.WriteLine("redPorsche travels " +
      redPorsche.Distance(31, .25) + " miles.");
  }
}

Illustrates how to assign default values to fields using initializers

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy
Publisher: Sybex;
ISBN: 0782129110
*/
/*
  Example5_2.cs illustrates how to assign default values 
  to fields using initializers
*/

// declare the Car class
class Car
{
  // declare the fields
  public string make = "Ford";
  public string model = "T";
  public string color;  // default value of null
  public int yearBuilt = 1910;
  // define the methods
  public void Start()
  {
    System.Console.WriteLine(model + " started");
  }
  public void Stop()
  {
    System.Console.WriteLine(model + " stopped");
  }
}

public class Example5_2
{
  public static void Main()
  {
    // create a Car object
    Car myCar = new Car();
    // display the default values for the Car object fields
    System.Console.WriteLine("myCar.make = " + myCar.make);
    System.Console.WriteLine("myCar.model = " + myCar.model);
    if (myCar.color == null)
    {
      System.Console.WriteLine("myCar.color is null");
    }
    System.Console.WriteLine("myCar.yearBuilt = " + myCar.yearBuilt);
  }
}

Illustrates how to declare classes, object references, and create objects

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy
Publisher: Sybex;
ISBN: 0782129110
*/
/*
  Example5_1.cs illustrates how to declare
  classes, object references, and create objects
*/

// declare the Car class
class Car
{
  // declare the fields
  public string make;
  public string model;
  public string color;
  public int yearBuilt;
  // define the methods
  public void Start()
  {
    System.Console.WriteLine(model + " started");
  }
  public void Stop()
  {
    System.Console.WriteLine(model + " stopped");
  }
}

public class Example5_1
{
  public static void Main()
  {
    // declare a Car object reference named myCar
    Car myCar;
    // create a Car object, and assign its address to myCar
    System.Console.WriteLine("Creating a Car object and assigning " +
      "its memory location to myCar");
    myCar = new Car();
    // assign values to the Car object"s fields using myCar
    myCar.make = "Toyota";
    myCar.model = "MR2";
    myCar.color = "black";
    myCar.yearBuilt = 1995;
    // display the field values using myCar
    System.Console.WriteLine("myCar details:");
    System.Console.WriteLine("myCar.make = " + myCar.make);
    System.Console.WriteLine("myCar.model = " + myCar.model);
    System.Console.WriteLine("myCar.color = " + myCar.color);
    System.Console.WriteLine("myCar.yearBuilt = " + myCar.yearBuilt);
    // call the methods using myCar
    myCar.Start();
    myCar.Stop();
    // declare another Car object reference and
    // create another Car object
    System.Console.WriteLine("Creating another Car object and " +
      "assigning its memory location to redPorsche");
    Car redPorsche = new Car();
    redPorsche.make = "Porsche";
    redPorsche.model = "Boxster";
    redPorsche.color = "red";
    redPorsche.yearBuilt = 2000;
    System.Console.WriteLine("redPorsche is a " + redPorsche.model);
    // change the object referenced by the myCar object reference
    // to the object referenced by redPorshe
    System.Console.WriteLine("Assigning redPorsche to myCar");
    myCar = redPorsche;
    System.Console.WriteLine("myCar details:");
    System.Console.WriteLine("myCar.make = " + myCar.make);
    System.Console.WriteLine("myCar.model = " + myCar.model);
    System.Console.WriteLine("myCar.color = " + myCar.color);
    System.Console.WriteLine("myCar.yearBuilt = " + myCar.yearBuilt);
    // assign null to myCar (myCar will no longer reference an object)
    myCar = null;
  }
}

illustrates how to use a "has a" relationship

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy
Publisher: Sybex;
ISBN: 0782129110
*/
/*
  Example6_5.cs illustrates how to use a "has a"
  relationship
*/

// declare the Engine class
class Engine
{
  // declare the fields
  public int cylinders;
  public int horsepower;
  // define the method
  public void Start()
  {
    System.Console.WriteLine("Engine started");
  }
}

// declare the Car class
class Car
{
  // declare the fields
  public string make;
  public Engine engine;  // Car has an Engine
  // define the method
  public void Start()
  {
    engine.Start();
  }
}

public class Example6_5
{
  public static void Main()
  {
    // declare a Car object reference named myCar
    System.Console.WriteLine("Creating a Car object");
    Car myCar = new Car();
    myCar.make = "Toyota";
    // Car objects have an Engine object
    System.Console.WriteLine("Creating an Engine object");
    myCar.engine = new Engine();
    myCar.engine.cylinders = 4;
    myCar.engine.horsepower = 180;
    // display the values for the Car and Engine object fields
    System.Console.WriteLine("myCar.make = " + myCar.make);
    System.Console.WriteLine("myCar.engine.cylinders = " +
      myCar.engine.cylinders);
    System.Console.WriteLine("myCar.engine.horsepower = " +
      myCar.engine.horsepower);
    // call the Car object"s Start() method
    myCar.Start();
  }
}

Illustrates nested classes

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy
Publisher: Sybex;
ISBN: 0782129110
*/
/*
  Example6_6.cs illustrates nested classes
*/

// declare the Car class
class Car
{
  // declare the Engine class
  public class Engine
  {
    // declare the Engine fields
    public int cylinders;
    public int horsepower;
    // define the Engine method
    public void Start()
    {
      System.Console.WriteLine("Engine started");
    }
  }
  // declare the Car fields
  public string make;
  public Engine engine;  // Car has an Engine
  // define the Car method
  public void Start()
  {
    engine.Start();
  }
}

public class Example6_6
{
  public static void Main()
  {
    // declare a Car object reference named myCar
    System.Console.WriteLine("Creating a Car object");
    Car myCar = new Car();
    myCar.make = "Toyota";
    // Car objects have an Engine object
    System.Console.WriteLine("Creating an Engine object");
    myCar.engine = new Car.Engine();
    myCar.engine.cylinders = 4;
    myCar.engine.horsepower = 180;
    // display the values for the Car and Engine object fields
    System.Console.WriteLine("myCar.make = " + myCar.make);
    System.Console.WriteLine("myCar.engine.cylinders = " +
      myCar.engine.cylinders);
    System.Console.WriteLine("myCar.engine.horsepower = " +
      myCar.engine.horsepower);
    // call the Car object"s Start() method
    myCar.Start();
  }
}

Multiple constructors in a class definition

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa
Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/
// Constrct.cs - Demonstrates the use of multiple constructors
//               in a class definition.
//
//               Compile this program with the following command line:
//                   C:>csc Constrct.cs
//
namespace nsConstructor
{
    using System;
    struct POINT
    {
        public POINT (int cx, int cy)
        {
            this.cx = cx;
            this.cy = cy;
        }
        public int cx;
        public int cy;
    }
    public class Constrct
    {
        static public void Main ()
        {
            clsRect rc1 = new clsRect();
            clsRect rc2 = new clsRect (10, 12, 84, 96);
            POINT pt1 = new POINT (10, 12);
            POINT pt2 = new POINT (84, 96);
            clsRect rc3 = new clsRect (pt1, pt2);
        }
    }
    class clsRect
    {
// The following constructor replaces the default constructor
        public clsRect ()
        {
            Console.WriteLine ("Default constructor called");
            m_Left = m_Top = m_Right = m_Bottom  = 0;
        }
        public clsRect (int cx1, int cy1, int cx2, int cy2)
        {
            Console.WriteLine ("Constructor 1 called");
            m_Left = cx1;
            m_Top = cy1;
            m_Right = cx2;
            m_Bottom = cy2;
        }
        public clsRect (POINT pt1, POINT pt2)
        {
            Console.WriteLine ("Constructor 2 called");
            m_Left = pt1.cx;
            m_Top = pt1.cy;
            m_Right = pt2.cx;
            m_Bottom = pt2.cy;
        }
        public POINT UpperLeft
        {
            get {return(new POINT(m_Left, m_Top));}
            set {m_Left = value.cx; m_Top = value.cy;}
        }
        public POINT LowerRight
        {
            get {return(new POINT(m_Right, m_Bottom));}
            set {m_Right = value.cx; m_Bottom = value.cy;}
        }
        private int m_Left;
        private int m_Top;
        private int m_Right;
        private int m_Bottom;
    }
}

Return an object

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
// Return an object. 
 
using System; 
 
class Rect { 
  int width; 
  int height; 
 
  public Rect(int w, int h) { 
    width = w; 
    height = h; 
  } 
 
  public int area() { 
    return width * height; 
  } 
 
  public void show() { 
    Console.WriteLine(width + " " + height); 
  } 
 
  /* Return a rectangle that is a specified 
     factor larger than the invoking rectangle. */ 
  public Rect enlarge(int factor) { 
    return new Rect(width * factor, height * factor); 
  } 
} 
  
public class RetObj { 
  public static void Main() {   
    Rect r1 = new Rect(4, 5); 
 
    Console.Write("Dimensions of r1: "); 
    r1.show(); 
    Console.WriteLine("Area of r1: " + r1.area()); 
 
    Console.WriteLine(); 
 
    // create a rectange that is twice as big as r1 
    Rect r2 = r1.enlarge(2); 
 
    Console.Write("Dimensions of r2: "); 
    r2.show(); 
    Console.WriteLine("Area of r2 " + r2.area()); 
  } 
}

Show name hiding in a derived class

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa
Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/
//
// Hide.cs -- Show name hiding in a derived class
//
//            Compile this program with the following command line:
//                C:>csc Hide.cs
//
namespace nsHide
{
    using System;
    using System.Reflection;
    
    public class Hide
    {
        static public void Main ()
        {
            clsBase Base = new clsBase();
            clsDerived Derived = new clsDerived ();
            Base.x = 42;
            Derived.x = 42;
            Console.WriteLine ("For the base class:");
            Console.WriteLine ("\tThe type stored in clsBase is " + Base.TypeOf());
            Console.WriteLine ("\tMathOp () returns {0,0:F3} for {1}", Base.MathOp(42), 42);
            Console.WriteLine ("\r\nFor the derived class:");
            Console.WriteLine ("\tThe type stored in clsDerived is " + Derived.TypeOf());
            Console.WriteLine ("\tMathOp () returns {0,0:F3} for {1}", Derived.MathOp(42), 42);
        }
    }
    class clsBase
    {
        protected int m_x;
        public int x
        {
           get {return (x);}
           set {m_x = value;}
        }
        public double MathOp (int val)
        {
            return (Math.Sqrt ((double) val));
        }
        public string TypeOf ()
        {
            return ("integer");
        }
    }
    class clsDerived : clsBase
    {
        new protected double m_x;
        new public double x
        {
           get {return (x);}
           set {m_x = value;}
        }
        new public double MathOp (int val)
        {
            return ((double) (val * val));
        }
        new public string TypeOf ()
        {
            return ("long");
        }
    }
}

simulate a bank account

 
using System;
public class BankAccount {
    public static int nNextAccountNumber = 1000;
    public int nAccountNumber;
    public double dBalance;
    
    public void InitBankAccount() {
        nAccountNumber = ++nNextAccountNumber;
        dBalance = 0.0;
    }
    public void Deposit(double dAmount) {
        if (dAmount > 0.0) {
            dBalance += dAmount;
        }
    }
    public double Withdraw(double dWithdrawal) {
        if (dBalance <= dWithdrawal) {
            dWithdrawal = dBalance;
        }
        dBalance -= dWithdrawal;
        return dWithdrawal;
    }
}

This program creates two Building objects

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
// This program creates two Building objects. 
 
  
using System;  
  
class Building {   
  public int floors;    // number of floors 
  public int area;      // total square footage of building 
  public int occupants; // number of occupants 
}   
   
// This class declares two objects of type Building.   
public class BuildingDemo1 {   
  public static void Main() {   
    Building house = new Building();   
    Building office = new Building(); 
 
    int areaPP; // area per person 
   
    // assign values to fields in house 
    house.occupants = 4;  
    house.area = 2500;  
    house.floors = 2;  
 
    // assign values to fields in office 
    office.occupants = 25;  
    office.area = 4200;  
    office.floors = 3;  
   
    // compute the area per person in house 
    areaPP = house.area / house.occupants;  
   
    Console.WriteLine("house has:\n  " + 
                      house.floors + " floors\n  " + 
                      house.occupants + " occupants\n  " + 
                      house.area + " total area\n  " + 
                      areaPP + " area per person"); 
 
    Console.WriteLine(); 
 
    // compute the area per person in office 
    areaPP = office.area / office.occupants;  
 
    Console.WriteLine("office has:\n  " + 
                      office.floors + " floors\n  " + 
                      office.occupants + " occupants\n  " + 
                      office.area + " total area\n  " + 
                      areaPP + " area per person"); 
  }   
}

Uses a class from Example16_3a.cs

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy
Publisher: Sybex;
ISBN: 0782129110
*/
/*
  Example16_3b.cs uses a class from Example16_3a.cs
*/
using System;
using StringSwitch;  // name space define in Example16_3c.cs
public class Example16_3b 
{
  public static void Main() 
  {
    string localString;
    MySwitch s = new MySwitch();
    s.inString="abcdef";
    s.upper(out localString);
    Console.WriteLine(localString);
  }
}
//===========================================================
/*
  Example16_3c.cs provides manifest information for Example 16_3
*/
using System.Reflection;
[assembly: AssemblyTitle("Example 16.3")]
[assembly: AssemblyVersion("1.0.0.0")]

//===========================================================
/*
  Example16_3a.cs creates a namespace with a single class
*/
using System;
namespace StringSwitch
{
  class MySwitch 
  {
    string privateString;
    public string inString 
    {
      get 
      {
        return privateString;
      }
      set
      {
        privateString = value;
      }
    }
    public void upper(out string upperString)
    {
      upperString = privateString.ToUpper();
    }
  }
}

Using Initializers

 

public class Product {
    public string make = "Ford";
    public string model = "T";
    public string color;  // default value of null
    public int yearBuilt = 1910;
    public void Start() {
        System.Console.WriteLine(model + " started");
    }
    public void Stop() {
        System.Console.WriteLine(model + " stopped");
    }
}
class MainClass {
    public static void Main() {
        Product myProduct = new Product();
        System.Console.WriteLine("myProduct.make = " + myProduct.make);
        System.Console.WriteLine("myProduct.model = " + myProduct.model);
        if (myProduct.color == null) {
            System.Console.WriteLine("myProduct.color is null");
        }
        System.Console.WriteLine("myProduct.yearBuilt = " + myProduct.yearBuilt);
    }
}

Variable in and out a class

/*
Learning C# 
by Jesse Liberty
Publisher: O"Reilly 
ISBN: 0596003765
*/
 using System;
 namespace heap
 {
     public class Dog
     {
         public int weight;
     }
    public class TesterClass
    {
       public void Run()
       {
           // create an integer
           int firstInt = 5;
           // create a second integer
           int secondInt = firstInt;
           // display the two integers
           Console.WriteLine("firstInt: {0} secondInt: {1}",
               firstInt, secondInt);
           // modify the second integer
           secondInt = 7;
           // display the two integers
           Console.WriteLine("firstInt: {0} secondInt: {1}",
               firstInt, secondInt);
           // create a dog
           Dog milo = new Dog();
           // assign a value to weight
           milo.weight = 5;
           // create a second reference to the dog
           Dog fido = milo;
           // display their values
           Console.WriteLine("Milo: {0}, fido: {1}",
               milo.weight, fido.weight);
           // assign a new weight to the second reference
           fido.weight = 7;
           // display the two values
           Console.WriteLine("Milo: {0}, fido: {1}",
               milo.weight, fido.weight);
       }
       static void Main()
       {
          TesterClass t = new TesterClass();
          t.Run();
       }
    }
 }