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Polymorphism and Abstraction
 

Characteristics of Inheritance
 

Namespaces and Inheritance

Imagine you had created a class named Person in a namespace named People as follows:

Source File: Persons.cs 
using System;

namespace People
{
	public class Person
	{
		private string _name;
		private string _gdr;

		public Person()
		{
			this._name = "Not Available";
			this._gdr  = "Unknown";
		}
		public Person(string name, string gender)
		{
			this._name = name;
			this._gdr  = gender;
		}

		private string FullName
		{
			get { return _name; }
			set { _name = value; }
		}

		private string Gender
		{
			get { return _gdr; }
			set { _gdr = value; }
		}
	}
}

If you decide to derive a class from it, remember that this class belongs to a namespace. To inherit from this class, the compiler will need to know the namespace in which the was created. Class inheritance that involves namespaces relies on qualification, like the calling of the members of a namespace. To derive a class from a class member of a namespace, type the name of the namespace, followed by the period operator ".", and followed by the name of the base namespace. Here is an example:

Source File: StaffMembers.cs 
using System;

namespace HighSchool
{
	public class Teacher : People.Person
	{
		private string _pos;

		public Teacher()
		{
			this._pos = "Staff Member";
		}

		public Teacher(string pos)
		{
			this._pos     = pos;
		}

		private string Position
		{
			get { return _pos; }
			set { _pos = value; }
		}
	}
}

If you need to call the class that was defined in a different namespace, remember to qualify its name with the scope access operator. Here is an example:

Source File: Exercise.cs 
using System;

class Exercise
{
	static void Main()
	{
		People.Person man = new People.Person("Hermine Sandt", "Male");
		HighSchool.Teacher staff = new HighSchool.Teacher("Vice Principal");

		Console.WriteLine();
	}
}

Alternatively, as mentioned in the past, to use the contents of a namespace, prior to calling a member of that namespace, you can type the using keyword followed by the name of the namespace. Here is an example:

Source File: Exercise.cs 
using System;
using People;
using HighSchool;

class Exercise
{
	static void Main()
	{
		Person man = new Person("Hermine Sandt", "Male");
		Teacher staff = new Teacher("Vice Principal");

		Console.WriteLine();
	}
}
 

Practical Learning Practical Learning: Using Inheritance With Namespaces
  1. Open Notepad and type the following:
      
    using System;

namespace FlatShapes
{
	class Square
	{
		private double _side;

		public Square()
		{
			_side = 0.00;
		}

		public Square(double s)
		{
			_side = s;
		}
	}

	class Rectangle
	{
		double _length;
		double _height;

		public Rectangle()
		{
			_length = 0.00;
			_height = 0.00;
		}

		public Rectangle(double L, double H)
		{
			_length = L;
			_height = H;
		}
	}
}
  2. Save the file in a new folder named Shapes1
  3. Save the file itself as Regulars.cs
  4. Start another instance of Notepad and type the following:
      
    using System;

class Exercise
{
	static void Main()
	{
		FlatShapes.Square Sq = new FlatShapes.Square(24.55);
	}
}
  5. Save the file as Exercise.cs in the same Shapes1 folder
  6. Open the Command Prompt and switch to the above Shapes1 folder
  7. To compile the project, type csc Exercise.cs Regulars.cs and press Enter
  8. To execute the project, type Exercise and press Enter
  9. Return to Notepad

Protected Members

To maintain a privileged relationship with its children, a parent class can make a set list of members available only to classes derived from it. With this relationship, some members of a parent class have a protected access level. Of course, as the class creator, it is your job to specify this relationship.

To create a member that derived classes only can access, type the protected keyword to its left. Here are examples:

Source File: Persons.cs 
using System;

namespace People
{
	public class Person
	{
		private string _name;
		private string _gdr;

		public Person()
		{
			this._name = "Not Available";
			this._gdr    = "Unknown";
		}
		public Person(string name, string gender)
		{
			this._name = name;
			this._gdr  = gender;
		}

		protected string FullName
		{
			get { return _name; }
			set { _name = value; }
		}

		protected string Gender
		{
			get { return _gdr; }
			set { _gdr = value; }
		}
		
		public void Show()
		{
			Console.WriteLine("Full Name: {0}", this.FullName);
			Console.WriteLine("Gender:    {0}", this.Gender);
		}
	}
}

You can access protected members only in derived classes. Therefore, if you instantiate a class outside, you can call only public members:

Source File: Exercise.cs 
using System;

class Exercise
{
	static void Main()
	{
		People.Person man = new People.Person("Hermine Sandt", "Male");

		Console.WriteLine("Staff Member");
		man.Show();

		Console.WriteLine();
	}
}

This would produce:

Staff Member
Full Name: Hermine Sandt
Gender:     Male

Virtual Members

We have just mentioned that you can create a new version of a member in a derived class for a member that already exists in the parent class. After doing this, when you call that member in your program, you need to make sure that the right member gets called, the member in the base class or the equivalent member in the derived class.

When you create a base class, if you anticipate that a certain property or method would need to be redefined in the derived class, you can indicate this to the compiler. On the other hand, while creating your classes, if you find out that you are customizing a property of method that already existed in the base class, you should let the compiler that you are providing a new version. In both cases, the common member should be created as virtual. To do this, in the base class, type the virtual keyword to the left of the property or method. Based on this, the Area property of our Circle class can be created as follows:

class Circle
{
	public virtual double Area
	{
		get
		{
			return Radius * Radius * 3.14159;
		}
	}
}

In fact, in C#, unlike C++, if you omit the virtual keyword, the compiler would display a warning.

When you derive a class from an abstract, since the methods (if any) of the abstract class were not implemented, you must implement each one of them in the derived class. When customizing virtual members in a derived class, to indicate that a member is already virtual in the base class and that you are defining a new version, type the override keyword to the left of its declaration. For example, the Area property in our Sphere class can be created as follows: 

class Sphere : Circle
{
	public override double  Area
	{
		get
		{
			return 4 * Radius * Radius * 3.14159;
		}
	}

	public double Volume
	{
		get
		{
			return 4 * 3.14159 * Radius * Radius * Radius;
		}
	}
}

In the same way, when implementing an abstract method of a class, type the override keyword to its left.

  

Practical Learning Practical Learning: Using Virtual Members
  1. Start a new instance of Notepad and type the following:
      
    class ShapeDescription
{
	public virtual string Description()
	{
		string Msg = "A quadrilateral is a geometric figure that has " +
			    "four sides and four angles.";
		return Msg;
	}
}
  2. Save the file as Quadrilaterals.cs in the Shapes1 folder
  3. Access the Regulars.cs file and override the Description method in the FlatShapes.Square and the FlatShapes.Rectangle classes as follows:
      
    using System;

namespace FlatShapes
{
	class Square : ShapeDescription
	{
		private double _side;

		public Square()
		{
			_side = 0.00;
		}

		public Square(double s)
		{
			_side = s;
		}
		
		public override string Description()
		{
			// Get the introduction from the parent
			string Introduction = base.Description() +
			"\nA square is a quadrilateral that has four " +
                                     "equal sides and four right angles";
		
			
			return Introduction;
		}
	}

	class Rectangle : ShapeDescription
	{
		double _length;
		double _height;

		public Rectangle()
		{
			_length = 0.00;
			_height = 0.00;
		}

		public Rectangle(double L, double H)
		{
			_length = L;
			_height = H;
		}
		
		public override string Description()
		{
			
			// Get the introduction from the parent
			string Introduction = base.Description();
			
			string Msg = Introduction +
                         "\nA rectangle is a quadrilateral that has adjacent " +
		"perpendicular sides. This implies that its four " +
				         "angles are right.";
			return Msg;
		}
	}
}
  4. Save the Regulars.cs file
  5. To access the new methods, access the Exercise.cs and change it as follows:
      
    using System;

class Exercise
{
	static void DisplaySquare(FlatShapes.Square S)
	{
		Console.WriteLine("Square Characteristics");
		Console.WriteLine("Description: {0}", S.Description());
	}
	
	static void DisplayRectangle(FlatShapes.Rectangle R)
	{
		Console.WriteLine("Rectangle Characteristics");
		Console.WriteLine("Description: {0}", R.Description());
	}

	static void Main()
	{
		FlatShapes.Square Sq = new FlatShapes.Square();
		FlatShapes.Rectangle Rect = new FlatShapes.Rectangle();

		Console.WriteLine("========================================");
		DisplaySquare(Sq);
		Console.WriteLine("========================================");
		DisplayRectangle(Rect);
		Console.WriteLine("========================================");
		
		Console.WriteLine();
	}
}
  6. Save the Exercise.cs
  7. Switch to the Command Prompt to the Shapes1 folder
  8. To compile the project, type csc Exercise.cs Regulars.cs Quadrilaterals.cs and press Enter
  9. To execute the project, type Exercise and press Enter. This would produce:
      
    ========================================
Square Characteristics
Description: A quadrilateral is a geometric figure that has four sides and four
angles.A square is a quadrilateral that has four equal sides and four right angles
========================================
Rectangle Characteristics
Description: A quadrilateral is a geometric figure that has four sides and four
angles.
A rectangle is a quadrilateral that has adjacent perpendicular sides. This implies 
that its four angles are right.
========================================
  10. Return to Notepad
 

Abstract Classes

In C#, you can create a class whose role is only meant to provide fundamental characteristics for other classes. This type of class cannot be used to declare a variable of the object. Such a class is referred to as abstract. Therefore, an abstract class can be created only to serve as a parent class for others. To create an abstract class, type the abstract keyword to the left of its name. Here is an example:

abstract class Ball
{
	protected int TypeOfSport;
	protected string Dimensions;
}

Practical Learning Practical Learning: Creating an Abstract Class
  1. To create an abstract class, in the Regulars.cs class, type the abstract keyword at the beginning of the class creation line:
      
    abstract class ShapeDescription
{
	public virtual string Description()
	{
		string Msg = "A quadrilateral is a geometric figure that has " +
					 "four sides and four angles.";
		return Msg;
	}
}
  2. Save the file

Abstract Properties and Methods

When creating a class that would mainly be used as base for future inheritance, you can create one or more properties and make them abstract. To do this, when creating the property, type the abstract keyword to its left. Because you would not define the property, you can simply type the get keyword and its semi-colon in the body of the property.

A method of a class also can be made abstract. An abstract method can be a member of only an abstract class. If you make a method abstract in a class, you must not implement the method. To create an abstract method, when creating its class, type the abstract keyword to the left of the method's name. End the declaration with a semi-colon and no body for the method since you cannot implement it. Here is an example:

public abstract class Ball
{
	protected int TypeOfSport;
	protected string Dimensions;

	public abstract CalculateArea();
}

In the same way, you can create as many properties and methods as you see fit. You can choose what properties and methods to make abstract. This is important for inheritance.

Practical Learning Practical Learning: Creating an Abstract Property
  1. To create an abstract property, access the Quadrilaterals.cs file and change its class as follows:
      
    abstract class ShapeDescription
{
	public abstract string Name { get; }

	public virtual string Description()
	{
		string Msg = "A quadrilateral is a geometric figure that has " +
			    "four sides and four angles.";
		return Msg;
	}
}
  2. Save the Quadrilaterals.cs file
  3. To define the property, open the Regulars.cs file and change it as follows:
      
    using System;

namespace FlatShapes
{
	class Square : ShapeDescription
	{
		private double _side;

		public Square()
		{
			_side = 0.00;
		}

		public Square(double s)
		{
			_side = s;
		}
		
		public override string Name
		{
			get { return "Square"; }
		}

		public override string Description()
		{
			// Get the introduction from the parent
			string Introduction = base.Description() +
			 "A square is a quadrilateral that has four " +
				  "equal sides and four right angles";
		
			
			return Introduction;
		}
	}

	class Rectangle : ShapeDescription
	{
		double _length;
		double _height;

		public Rectangle()
		{
			_length = 0.00;
			_height = 0.00;
		}

		public Rectangle(double L, double H)
		{
			_length = L;
			_height = H;
		}
		
		public override string Name
		{
			get { return "Rectangle"; }
		}

		public override string Description()
		{
			
			// Get the introduction from the parent
			string Introduction = base.Description();
			
			string Msg = Introduction +
                         "\nA rectangle is a quadrilateral that has adjacent " +
			"perpendicular sides. This implies that its four " +
		         "angles are right.";
			return Msg;
		}
	}
}
  4. Save the Regulars.cs file
  5. To include the new property in the test, access the Exercise.cs file and change it as follows:
      
    using System;

class Exercise
{
	static void DisplaySquare(FlatShapes.Square S)
	{
		Console.WriteLine("Square Characteristics");
		Console.WriteLine("Name:        {0}", S.Name);
		Console.WriteLine("Description: {0}", S.Description());
	}
	
	static void DisplayRectangle(FlatShapes.Rectangle R)
	{
		Console.WriteLine("Rectangle Characteristics");
		Console.WriteLine("Name:        {0}", R.Name);
		Console.WriteLine("Description: {0}", R.Description());
	}

	static void Main()
	{
		FlatShapes.Square Sq = new FlatShapes.Square();
		FlatShapes.Rectangle Rect = new FlatShapes.Rectangle();

		Console.WriteLine("========================================");
		DisplaySquare(Sq);
		Console.WriteLine("========================================");
		DisplayRectangle(Rect);
		Console.WriteLine("========================================");
		
		Console.WriteLine();
	}
}
  6. Save the Exercise.cs
  7. To compile the project, type csc Exercise.cs Regulars.cs Quadrilaterals.cs and press Enter
  8. To execute the project, type Exercise and press Enter. This would produce:
      
    ========================================
Square Characteristics
Name:        Square
Description: A quadrilateral is a geometric figure that has four sides and four
angles.A square is a quadrilateral that has four equal sides and four right angl
es
========================================
Rectangle Characteristics
Name:        Rectangle
Description: A quadrilateral is a geometric figure that has four sides and four
angles.
A rectangle is a quadrilateral that has adjacent perpendicular sides. This impli
es that its four angles are right.
========================================
  9. Return to Notepad

Sealed Classes

Any of the classes we have used so far in our lessons can be inherited from. If you create a certain class and don't want anybody to derive another class from it, you can mark it as sealed. In other words, a sealed class is one that cannot serve as base for another class.

To mark a class as sealed, type the sealed keyword to its left. Here is an example:

public sealed class Ball
{
	public int TypeOfSport;
	public string Dimensions;
}

Interfaces
 

Introduction

Imagine you start creating a class and, while implementing or testing it, you find out that this particular class can be instead as a general base that other classes can be derived from. An interface is a special class whose purpose is to serve as a template that actual classes can be based on.

An interface is primarily created like a class: it has a name, a body and can have members. To create an interface, instead of the class keyword, you use the interface keyword. By convention, the name of an interface starts with I. Here is an example:

interface ICourtDimensions
{
}

Practical Learning Practical Learning: Introducing Interfaces
  1. Access the Quadrilaterals.cs file. To create an interface, change the file as follows:
      
    interface IQuadrilateral
{
}

abstract class ShapeDescription
{
	public abstract string Name { get; }

	public virtual string Description()
	{
		string Msg = "A quadrilateral is a geometric figure that has " +
					 "four sides and four angles.";
		return Msg;
	}
}
  2. Save the file

The Members of an Interface

As done for a class, the members of an interface are listed in its body. In an interface, you cannot declare fields like those we have used in other classes. Instead, if you want some type of member variable, you can create a property. If you create a property in an interface, you cannot define that property. One of the rules of an interface is that you cannot define any of its members. This is also valid for its properties. Therefore, if you create a property in an interface:

  • You can indicate that it would be read-only by adding it an empty getter. Here is an example:
      
    public interface ICourtDimensions
{
	double Length { get; }
}
  • You can indicate that it would be write-only. Here is an example:
      
    public interface ICourtDimensions
{
	double Length { set; }
}
  • You can indicate that it would be used to write values to it and to read values from it. Here is an example:
      
    public interface ICourtDimensions
{
	double Length { get; set; }
}

In the same way, you can create as many properties as you judge them necessary in an interface. Besides the properties, an interface can also have other types of members such as methods. Here is an example of an interface that has one read-only property named NameOfSport, one read/write property named NumberOfPlayers, and one method named SportCharacteristics:

public interface IBall
{
	int NumberOfPlayers
	{
		get;
		set;
	}

	string NameOfSport
	{
		get;
	}

	void SportCharacteristics();
}

Practical Learning Practical Learning: Creating Members of an Interface
  1. To create a member int the new interface, access the Quadrilateral.cs file and change it as follows:
      
    interface IQuadrilateral
{
	double Area { get; }
}

abstract class ShapeDescription
{
	public abstract string Name { get; }

	public virtual string Description()
	{
		string Msg = "A quadrilateral is a geometric figure that has " +
			    "four sides and four angles.";
		return Msg;
	}
}
  2. Save the file

An Interface as a Base Class

An interface is mostly used to lay a foundation for other classes. For this reason, it is the prime candidate for class derivation. To derive from an interface, use the same technique we have applied in inheritance so far. Here is an example of a class named SportBall that derives from an interface named ISportType:

public class SportBall : ISportType
{
	int players;
	string sport;
}

Just as you can derive a class from an interface, you can create an interface that itself is based on another interface. Here is an example:

public interface ISportType : IBall
{
	SportCategory Type
	{
		get;
	}
}

The C# language doesn't allow multiple inheritance which is the ability to create a class based on more than one class. Multiple inheritance is allowed only if the bases are interfaces. To create multiple inheritance, separate the names of interface with a comma. Here is an example:

public interface ISportType : IBall, ICourtDimensions
{
	SportCategory Type
	{
		get;
	}
}

You can also involve a class as parent in a multiple inheritance scenario but there must be only one class. Here is an example in which a class called Sports derives from one class and various interfaces:

public interface Sports: Player, IBall, ICourtDimensions
{
}

Practical Learning Practical Learning: Inheriting From an Interface
  1. To inherit an interface from another interface, access the Quadrilateral.cs file and change it as follows:
      
    interface IQuadrilateral
{
	double Area { get; }
}

abstract class ShapeDescription
{
	public abstract string Name { get; }

	public virtual string Description()
	{
		string Msg = "A quadrilateral is a geometric figure that has " +
			    "four sides and four angles.";
		return Msg;
	}
}

interface IRightAngles : IQuadrilateral
{
	double Base { get; set; }
	double Height { get; set; }
	double Perimeter { get; }
}
  2. Save the file
  3. To inherit a class from an interface, access the Regulars.cs file and change it as follows:
      
    using System;

namespace FlatShapes
{
	class Square : ShapeDescription, IRightAngles
	{
		. . . No Change
	}

	class Rectangle : ShapeDescription, IRightAngles
	{
		. . . No Change
	}
}
  4. Save the file

Implementation of Derived Classes of an Interface

After creating an interface, you can derive other interfaces or other classes from it. If you are deriving other interfaces from an interface, you can just proceed as you see fit. For example, you can add or not add one or more new properties, you can add or not add one or more properties, etc. Here is an example:

Source File: Preparation.cs 
public enum SportCategory
{
	SinglePlayer,
	Collective,
	Unknown
}

public interface ICourtDimensions
{
	double Length { get; set; }
	double Width  { get; set; }
}

public interface IBall
{
	int NumberOfPlayers
	{
		get;
		set;
	}

	string NameOfSport
	{
		get;
	}

	void SportCharacteristics();
}

public interface ISportType : IBall, ICourtDimensions
{
	SportCategory Type
	{
		get;
	}
}

If you derive a class, from an interface, you must implement all properties that created in the interface. This means that you must define them so that, when a variable is declared of that class, the properties have meaning. In the same way, if you create a class that is based on an interface, you must implement all methods that were declared in the interface. If you derive a class from an interface that itself was derived from another interface, in your class, you must define all properties that were created in the whole lineage and you must implement all methods that were created in the parent and grant-parent interfaces. Here is an example:

Source File: Sport.cs 
using System;

public class SportBall : ISportType
{
	int players;
	string sport;
	SportCategory _type;
	double Len;
	double Wdt;
    
	public SportBall(int nbr, SportCategory tp, string name)
	{
		players = nbr;
		_type   = tp;
		sport   = name;
	}

	public int NumberOfPlayers
	{
		get	{ return players;}
		set	{ players = value;}
	}

	public string NameOfSport
	{
		get	{ return sport; }
	}

	public SportCategory Type
	{
		get	{ return _type; }
	}

	public double Length
	{
		get { return Len; }
		set { Len = value; }
	}

	public double Width
	{
		get { return Wdt; }
		set { Wdt = value; }
	}

	public void SportCharacteristics()
	{
		Console.WriteLine("Sport Characteristics");
		Console.WriteLine("Name of Sport: {0}", NameOfSport);
		Console.WriteLine("Type of Sport: {0}", Type);
		Console.WriteLine("# of Players:  {0}", NumberOfPlayers);
		Console.WriteLine("Court Dimensions: {0}m x {1}m", Len, Wdt);
	}
}

Once the class is ready, you can then use it as you see fit. Here is an example:
Source File: Exercise.cs 
using System;

class Exercise
{
	static void Main()
	{
		SportBall volley = new SportBall(6, SportCategory.Collective, "Volley Ball");
		volley.Length = 18;
		volley.Width  = 9;
		volley.SportCharacteristics();

		Console.WriteLine();

		SportBall tennis = new SportBall(1, SportCategory.SinglePlayer, "Table Tennis");
		tennis.Length = 23.7;
		tennis.Width  = 8.25;
		tennis.SportCharacteristics();

		Console.WriteLine();
	}
}

This would produce:

Sport Characteristics
Name of Sport: Volley Ball
Type of Sport: Collective
# of Players:  6
Court Dimensions: 18m x 9m

Sport Characteristics
Name of Sport: Table Tennis
Type of Sport: SinglePlayer
# of Players:  1
Court Dimensions: 23.7m x 8.25m

Practical Learning Practical Learning: Implementing Derived Members of an Interface
  1. To implement the members of an interface, access the Regulars.cs file and change it as follows:
      
    using System;

namespace FlatShapes
{
	class Square : ShapeDescription, IRightAngles
	{
		private double _side;

		public Square()
		{
			_side = 0.00;
		}

		public Square(double s)
		{
			_side = s;
		}
		
		public override string Name
		{
			get { return "Square"; }
		}

		public override string Description()
		{
			// Get the introduction from the parent
			string Introduction = base.Description() +
				"A square is a quadrilateral that has four " +
				  "equal sides and four right angles";
		
			
			return Introduction;
		}
		
		public double Base
		{
			get
			{
				return (_side < 0) ? 0.00 : _side;
			}
			set
			{
				_side = value;
			}
		}

		public double Height
		{
			get
			{
				return (_side < 0) ? 0.00 : _side;
			}
			set
			{
				_side = value;
			}
		}

		public double Area
		{
			get
			{
				return Base * Base;
			}
		}

		public double Perimeter
		{
			get
			{
				return Base * 4;
			}
		}
	}

	class Rectangle : ShapeDescription, IRightAngles
	{
		double _length;
		double _height;

		public Rectangle()
		{
			_length = 0.00;
			_height = 0.00;
		}

		public Rectangle(double L, double H)
		{
			_length = L;
			_height = H;
		}
		
		public override string Name
		{
			get { return "Rectangle"; }
		}

		public override string Description()
		{
			
			// Get the introduction from the parent
			string Introduction = base.Description();
			
			string Msg = Introduction +
                         "\nA rectangle is a quadrilateral that has adjacent " +
			"perpendicular sides. This implies that its four " +
				         "angles are right.";
			return Msg;
		}
		
		public double Base
		{
			get
			{
				return _length;
			}
			set
			{
				_length = value;
			}
		}

		public double Height
		{
			get
			{
				return _height;
			}
			set
			{
				_height = value;
			}
		}

		public double Area
		{
			get
			{
				return Base * Height;
			}
		}

		public double Perimeter
		{
			get
			{
				return 2 * (Base + Height);
			}
		}
	}
}
  2. Save the file
  3. To test the new properties, access the Exercise.cs file and change it as follows:
      
    using System;

class Exercise
{
	static FlatShapes.Square CreateASquare()
	{
		double side;

		Console.Write("Enter the side of the square: ");
		side = double.Parse(Console.ReadLine());
	
		FlatShapes.Square Sqr = new FlatShapes.Square(side);
		return Sqr;
	}
	
	static void DisplaySquare(FlatShapes.Square S)
	{
		Console.WriteLine("Square Characteristics");
		Console.WriteLine("Name:        {0}", S.Name);
		Console.WriteLine("Description: {0}", S.Description());
		Console.WriteLine("----------------------------");
		Console.WriteLine("Side:        {0}", S.Base);
		Console.WriteLine("Perimeter:   {0}", S.Perimeter);
		Console.WriteLine("Area:        {0}", S.Area);
	}
	
	
	static FlatShapes.Rectangle CreateARectangle()
	{
		double Len, Hgt;

		Console.WriteLine("Enter the dimensions of the rectangle");
		Console.Write("Base:   ");
		Len = double.Parse(Console.ReadLine());
		Console.Write("Height: ");
		Hgt = double.Parse(Console.ReadLine());

		FlatShapes.Rectangle Recto = new FlatShapes.Rectangle(Len, Hgt);
		return Recto;
	}

	static void DisplayRectangle(FlatShapes.Rectangle R)
	{
		Console.WriteLine("Rectangle Characteristics");
		Console.WriteLine("Name:        {0}", R.Name);
		Console.WriteLine("Description: {0}", R.Description());
		Console.WriteLine("----------------------------");
		Console.WriteLine("Base:        {0}", R.Base);
		Console.WriteLine("Height:      {0}", R.Height);
		Console.WriteLine("Perimeter:   {0}", R.Perimeter);
		Console.WriteLine("Area:        {0}", R.Area);
	}

	static void Main()
	{
		FlatShapes.Square Sq = new FlatShapes.Square();
		FlatShapes.Rectangle Rect = new FlatShapes.Rectangle();

		Sq   = CreateASquare();
		Rect = CreateARectangle();

		Console.WriteLine("============================");
		DisplaySquare(Sq);
		Console.WriteLine("============================");
		DisplayRectangle(Rect);
		Console.WriteLine("============================");
		
		Console.WriteLine();
	}
}
  4. To compile the project, type csc Exercise.cs Regulars.cs Quadrilaterals.cs and press Enter
  5. To execute the project, type Exercise and press Enter. This would produce:
      
    Enter the side of the square: 24.55
Enter the dimensions of the rectangle
Base:   32.25
Height: 26.85
============================
Square Characteristics
Name:        Square
Description: A quadrilateral is a geometric figure that has four sides and four
angles.A square is a quadrilateral that has four equal sides and four right angl
es
----------------------------
Side:        24.55
Perimeter:   98.2
Area:        602.7025
============================
Rectangle Characteristics
Name:        Rectangle
Description: A quadrilateral is a geometric figure that has four sides and four
angles.
A rectangle is a quadrilateral that has adjacent perpendicular sides. This impli
es that its four angles are right.
----------------------------
Base:        32.25
Height:      26.85
Perimeter:   118.2
Area:        865.9125
============================
  6. Return to Notepad
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