Thursday, 28 April 2016

C# OOPS

A Jagged array is an array of arrays.
You can initialize a jagged array as −
int[][] scores = new int[2][]{new int[]{92,93,94},new int[]{85,66,87,88}};
Where, scores is an array of two arrays of integers - scores[0] is an array of 3 integers and scores[1] is an array of 4 integers.
There are three ways that parameters can be passed to a method −
  • Value parameters − This method copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument.
  • Reference parameters − This method copies the reference to the memory location of an argument into the formal parameter. This means that changes made to the parameter affect the argument.
  • Output parameters − This method helps in returning more than one value.



Yes! Using output parameters. A return statement can be used for returning only one value from a function. However, using output parameters, you can return two values from a function.
Output parameters are similar to reference parameters, except that they transfer data out of the method rather than into it. Reference parameter copies the reference to the memory location of an argument into the formal parameter. This means that changes made to the parameter affect the argument.
A namespace is designed for providing a way to keep one set of names separate from another. The class names declared in one namespace does not conflict with the same class names declared in another.
using keyword is used to include a namespace in the program. A program generally has multiple using statements.
Value type variables can be assigned a value directly. They are derived from the class System.ValueType.
The value types directly contain data. Some examples are int, char, and float, which stores numbers, alphabets, and floating point numbers, respectively. When you declare an int type, the system allocates memory to store the value.
The reference types do not contain the actual data stored in a variable, but they contain a reference to the variables.
In other words, they refer to a memory location. Using multiple variables, the reference types can refer to a memory location. If the data in the memory location is changed by one of the variables, the other variable automatically reflects this change in value. Example of built-in reference types are: object, dynamic, and string.
The Object Type is the ultimate base class for all data types in C# Common Type System (CTS). Object is an alias for System.Object class. The object types can be assigned values of any other types, value types, reference types, predefined or user-defined types. However, before assigning values, it needs type conversion.
When a value type is converted to object type, it is called boxing.
When an object type is converted to a value type, it is called unboxing.
You can store any type of value in the dynamic data type variable. Type checking for these types of variables takes place at run-time.
Syntax for declaring a dynamic type is −
dynamic <variable_name> = value;
For example,

 
dynamic d = 20;
Dynamic types are similar to object types except that type checking for object type variables takes place at compile time, whereas that for the dynamic type variables takes place at run time.



Pointer type variables store the memory address of another type. Pointers in C# have the same capabilities as the pointers in C or C++.
Syntax for declaring a pointer type is −
type* identifier;
For example

 
char* cptr;
int* iptr;
is operator determines whether an object is of a certain type.
If( Ford is Car) // checks if Ford is an object of the Car class.
as operator casts without raising an exception if the cast fails.

 
Object obj = new StringReader("Hello");
StringReader r = obj as StringReader;
Encapsulation is defined 'as the process of enclosing one or more items within a physical or logical package'. Encapsulation, in object oriented programming methodology, prevents access to implementation details.
Encapsulation is defined 'as the process of enclosing one or more items within a physical or logical package'. Encapsulation, in object oriented programming methodology, prevents access to implementation details.
Abstraction and encapsulation are related features in object oriented programming. Abstraction allows making relevant information visible and encapsulation enables a programmer toimplement the desired level of abstraction.
Encapsulation is implemented by using access specifiers. Anaccess specifier defines the scope and visibility of a class member. C# supports the following access specifiers:
  • Public
  • Private
  • Protected
  • Internal
  • Protected internal
Public Access Specifier
Public access specifier allows a class to expose its member variables and member functions to other functions and objects. Any public member can be accessed from outside the class.
The following example illustrates this:
using System;
namespace RectangleApplication
{
   class Rectangle
   {
      //member variables
      public double length;
      public double width;
      
      public double GetArea()
      {
         return length * width;
      }
      public void Display()
      {
         Console.WriteLine("Length: {0}", length);
         Console.WriteLine("Width: {0}", width);
         Console.WriteLine("Area: {0}", GetArea());
      }
   }//end class Rectangle
   
   class ExecuteRectangle
   {
      static void Main(string[] args)
      {
         Rectangle r = new Rectangle();
         r.length = 4.5;
         r.width = 3.5;
         r.Display();
         Console.ReadLine();
      }
   }
}
When the above code is compiled and executed, it produces the following result:
Length: 4.5
Width: 3.5
Area: 15.75
In the preceding example, the member variables length and width are declared public, so they can be accessed from the function Main() using an instance of the Rectangle class, namedr.
The member function Display() and GetArea() can also access these variables directly without using any instance of the class.
The member functions Display() is also declared public, so it can also be accessed from Main() using an instance of the Rectangle class, named r.

Private Access Specifier

Private access specifier allows a class to hide its member variables and member functions from other functions and objects. Only functions of the same class can access its private members. Even an instance of a class cannot access its private members.
The following example illustrates this:
using System;
namespace RectangleApplication 
{
   class Rectangle
   {
      //member variables
      private double length;
      private double width;
      
      public void Acceptdetails()
      {
         Console.WriteLine("Enter Length: ");
         length = Convert.ToDouble(Console.ReadLine());
         Console.WriteLine("Enter Width: ");
         width = Convert.ToDouble(Console.ReadLine());
      }
      public double GetArea()
      {
         return length * width;
      }
      public void Display()
      {
         Console.WriteLine("Length: {0}", length);
         Console.WriteLine("Width: {0}", width);
         Console.WriteLine("Area: {0}", GetArea());
      }
   }//end class Rectangle
   
   class ExecuteRectangle
   {
      static void Main(string[] args)
      {
         Rectangle r = new Rectangle();
         r.Acceptdetails();
         r.Display();
         Console.ReadLine();
      }
   }
}
When the above code is compiled and executed, it produces the following result:
Enter Length:
4.4
Enter Width:
3.3
Length: 4.4
Width: 3.3
Area: 14.52
In the preceding example, the member variables length and width are declared private, so they cannot be accessed from the function Main(). The member functions AcceptDetails() andDisplay() can access these variables. Since the member functions AcceptDetails() and Display() are declared public, they can be accessed from Main() using an instance of the Rectangle class, named r.

Protected Access Specifier

Protected access specifier allows a child class to access the member variables and member functions of its base class. This way it helps in implementing inheritance. We will discuss this in more details in the inheritance chapter.

Internal Access Specifier

Internal access specifier allows a class to expose its member variables and member functions to other functions and objects in the current assembly. In other words, any member with internal access specifier can be accessed from any class or method defined within the application in which the member is defined.
The following program illustrates this:
using System;
namespace RectangleApplication
{
   class Rectangle
   {
      //member variables
      internal double length;
      internal double width;
      
      double GetArea()
      {
         return length * width;
      }
      public void Display()
      {
         Console.WriteLine("Length: {0}", length);
         Console.WriteLine("Width: {0}", width);
         Console.WriteLine("Area: {0}", GetArea());
      }
   }//end class Rectangle
   
   class ExecuteRectangle
   {
      static void Main(string[] args)
      {
         Rectangle r = new Rectangle();
         r.length = 4.5;
         r.width = 3.5;
         r.Display();
         Console.ReadLine();
      }
   }
}
When the above code is compiled and executed, it produces the following result:
Length: 4.5
Width: 3.5
Area: 15.75
In the preceding example, notice that the member functionGetArea() is not declared with any access specifier. Then what would be the default access specifier of a class member if we don't mention any? It is private.

Protected Internal Access Specifier


The protected internal access specifier allows a class to hide its member variables and member functions from other class objects and functions, except a child class within the same application. This is also used while implementing inheritance.
Encapsulation is implemented by using access specifiers.
An access specifier defines the scope and visibility of a class member.
Public access specifier allows a class to expose its member variables and member functions to other functions and objects. Any public member can be accessed from outside the class.
Private access specifier allows a class to hide its member variables and member functions from other functions and objects. Only functions of the same class can access its private members. Even an instance of a class cannot access its private members.
Protected access specifier allows a child class to access the member variables and member functions of its base class. This way it helps in implementing inheritance.
Internal access specifier allows a class to expose its member variables and member functions to other functions and objects in the current assembly. In other words, any member with internal access specifier can be accessed from any class or method defined within the application in which the member is defined.
The protected internal access specifier allows a class to hide its member variables and member functions from other class objects and functions, except a child class within the same application. This is also used while implementing inheritance.
C# provides a special data types, the nullable types, to which you can assign normal range of values as well as null values.
For example, you can store any value from -2,147,483,648 to 2,147,483,647 or null in a Nullable<Int32> variable. Similarly, you can assign true, false, or null in a Nullable<bool> variable.
The null coalescing operator is used with the nullable value types and reference types. It is used for converting an operand to the type of another nullable (or not) value type operand, where an implicit conversion is possible.
If the value of the first operand is null, then the operator returns the value of the second operand, otherwise it returns the value of the first operand.
By using the params keyword, a method parameter can be specified which takes a variable number of arguments or even no argument.
No! additional parameters are not permitted after the params keyword in a method declaration. Only one params keyword is allowed in a method declaration.
The Array class is the base class for all the arrays in C#. It is defined in the System namespace. The Array class provides various properties and methods to work with arrays.
Using Array.sort(array) function. It sorts the elements in an entire one-dimensional Array using the IComparable implementation of each element of the Array.
First sort the array using Array.sort(array) then reverse the same using Array.reverse(array) method.
In C#, a structure is a value type data type. It helps you to make a single variable hold related data of various data types. The struct keyword is used for creating a structure.
Structures are used to represent a record. To define a structure, you must use the struct statement. The struct statement defines a new data type, with more than one member for your program.

 
struct Books
{
   public string title;
   public string author;
   public string subject;
   public int book_id;
};
The following program shows the use of the structure:
using System;
struct Books
{
   public string title;
   public string author;
   public string subject;
   public int book_id;
};  

public class testStructure
{
   public static void Main(string[] args)
   {

      Books Book1;   /* Declare Book1 of type Book */
      Books Book2;   /* Declare Book2 of type Book */

      /* book 1 specification */
      Book1.title = "C Programming";
      Book1.author = "Nuha Ali"; 
      Book1.subject = "C Programming Tutorial";
      Book1.book_id = 6495407;

      /* book 2 specification */
      Book2.title = "Telecom Billing";
      Book2.author = "Zara Ali";
      Book2.subject =  "Telecom Billing Tutorial";
      Book2.book_id = 6495700;

      /* print Book1 info */
      Console.WriteLine( "Book 1 title : {0}", Book1.title);
      Console.WriteLine("Book 1 author : {0}", Book1.author);
      Console.WriteLine("Book 1 subject : {0}", Book1.subject);
      Console.WriteLine("Book 1 book_id :{0}", Book1.book_id);

      /* print Book2 info */
      Console.WriteLine("Book 2 title : {0}", Book2.title);
      Console.WriteLine("Book 2 author : {0}", Book2.author);
      Console.WriteLine("Book 2 subject : {0}", Book2.subject);
      Console.WriteLine("Book 2 book_id : {0}", Book2.book_id);       

      Console.ReadKey();

   }
}
When the above code is compiled and executed, it produces the following result:

Book 1 title : C Programming
Book 1 author : Nuha Ali
Book 1 subject : C Programming Tutorial
Book 1 book_id : 6495407
Book 2 title : Telecom Billing
Book 2 author : Zara Ali
Book 2 subject : Telecom Billing Tutorial
Book 2 book_id : 6495700
Classes and Structures have the following basic differences:
  • classes are reference types and structs are value types.
  • structures do not support inheritance.
  • structures cannot have default constructor.
An enumeration is a set of named integer constants. An enumerated type is declared using the enum keyword.
C# enumerations are value data type. In other words, enumeration contains its own values and cannot inherit or cannot pass inheritance.

Example

The following example demonstrates use of enum variable:
using System;
namespace EnumApplication
{
   class EnumProgram
   {
      enum Days { Sun, Mon, tue, Wed, thu, Fri, Sat };

      static void Main(string[] args)
      {
         int WeekdayStart = (int)Days.Mon;
         int WeekdayEnd = (int)Days.Fri;
         Console.WriteLine("Monday: {0}", WeekdayStart);
         Console.WriteLine("Friday: {0}", WeekdayEnd);
         Console.ReadKey();
      }
   }
}
When the above code is compiled and executed, it produces the following result:

Monday: 1
Friday: 5
Default access specifier for a class type is internal.
Default access for the members is private.
One of the most important concepts in object-oriented programming is inheritance. Inheritance allows us to define a class in terms of another class, which makes it easier to create and maintain an application. This also provides an opportunity to reuse the code functionality and speeds up implementation time.
When creating a class, instead of writing completely new data members and member functions, the programmer can designate that the new class should inherit the members of an existing class. This existing class is called the base class, and the new class is referred to as the derived class.
The idea of inheritance implements the IS-A relationship. For example, mammal IS A animal, dog IS-A mammal hence dog IS-A animal as well, and so on.
No! C# does not support multiple inheritance.
A class can be derived from more than one class or interface, which means that it can inherit data and functions from multiple base classes or interfaces. The syntax used in C# for creating derived classes is as follows:
<acess-specifier> class <base_class>
{
   ...
}
class <derived_class> : <base_class>
{
   ...
}
The word polymorphism means having many forms. In object-oriented programming paradigm, polymorphism is often expressed as 'one interface, multiple functions'.

Static Polymorphism

The mechanism of linking a function with an object during compile time is called early binding. It is also called static binding. C# provides two techniques to implement static polymorphism. They are:
  • Function overloading
  • Operator overloading
We discuss operator overloading in next chapter.

Function Overloading

You can have multiple definitions for the same function name in the same scope. The definition of the function must differ from each other by the types and/or the number of arguments in the argument list. You cannot overload function declarations that differ only by return type.
The following example shows using function print() to print different data types:
using System;
namespace PolymorphismApplication
{
   class Printdata
   {
      void print(int i)
      {
         Console.WriteLine("Printing int: {0}", i );
      }

      void print(double f)
      {
         Console.WriteLine("Printing float: {0}" , f);
      }

      void print(string s)
      {
         Console.WriteLine("Printing string: {0}", s);
      }
      static void Main(string[] args)
      {
         Printdata p = new Printdata();
         
         // Call print to print integer
         p.print(5);
         
         // Call print to print float
         p.print(500.263);
         
         // Call print to print string
         p.print("Hello C++");
         Console.ReadKey();
      }
   }
}
When the above code is compiled and executed, it produces the following result:
Printing int: 5
Printing float: 500.263
Printing string: Hello C++

Dynamic Polymorphism

C# allows you to create abstract classes that are used to provide partial class implementation of an interface. Implementation is completed when a derived class inherits from it. Abstractclasses contain abstract methods, which are implemented by the derived class. The derived classes have more specialized functionality.
Here are the rules about abstract classes:
  • You cannot create an instance of an abstract class
  • You cannot declare an abstract method outside an abstract class
  • When a class is declared sealed, it cannot be inherited, abstract classes cannot be declared sealed.
The following program demonstrates an abstract class:
using System;
namespace PolymorphismApplication
{
   abstract class Shape
   {
      public abstract int area();
   }
   class Rectangle:  Shape
   {
      private int length;
      private int width;
      public Rectangle( int a=0, int b=0)
      {
         length = a;
         width = b;
      }
      public override int area ()
      { 
         Console.WriteLine("Rectangle class area :");
         return (width * length); 
      }
   }

   class RectangleTester
   {
      static void Main(string[] args)
      {
         Rectangle r = new Rectangle(10, 7);
         double a = r.area();
         Console.WriteLine("Area: {0}",a);
         Console.ReadKey();
      }
   }
}
When the above code is compiled and executed, it produces the following result:
Rectangle class area :
Area: 70
When you have a function defined in a class that you want to be implemented in an inherited class(es), you use virtual functions. The virtual functions could be implemented differently in different inherited class and the call to these functions will be decided at runtime.
Dynamic polymorphism is implemented by abstract classes andvirtual functions.
The following program demonstrates this:
using System;
namespace PolymorphismApplication
{
   class Shape 
   {
      protected int width, height;
      public Shape( int a=0, int b=0)
      {
         width = a;
         height = b;
      }
      public virtual int area()
      {
         Console.WriteLine("Parent class area :");
         return 0;
      }
   }
   class Rectangle: Shape
   {
      public Rectangle( int a=0, int b=0): base(a, b)
      {

      }
      public override int area ()
      {
         Console.WriteLine("Rectangle class area :");
         return (width * height); 
      }
   }
   class Triangle: Shape
   {
      public Triangle(int a = 0, int b = 0): base(a, b)
      {
      
      }
      public override int area()
      {
         Console.WriteLine("Triangle class area :");
         return (width * height / 2); 
      }
   }
   class Caller
   {
      public void CallArea(Shape sh)
      {
         int a;
         a = sh.area();
         Console.WriteLine("Area: {0}", a);
      }
   }  
   class Tester
   {
      
      static void Main(string[] args)
      {
         Caller c = new Caller();
         Rectangle r = new Rectangle(10, 7);
         Triangle t = new Triangle(10, 5);
         c.CallArea(r);
         c.CallArea(t);
         Console.ReadKey();
      }
   }
}
When the above code is compiled and executed, it produces the following result:

Rectangle class area:
Area: 70
Triangle class area:
Area: 25
Polymorphism can be static or dynamic. In static polymorphism, the response to a function is determined at the compile time. In dynamic polymorphism, it is decided at run-time.
C# provides two techniques to implement static polymorphism. They are:
  • Function overloading
  • Operator overloading
The mechanism of linking a function with an object during compile time is called early binding. It is also called static binding.
You can have multiple definitions for the same function name in the same scope. The definition of the function must differ from each other by the types and/or the number of arguments in the argument list. You cannot overload function declarations that differ only by return type.
Dynamic polymorphism is implemented by abstract classes and virtual functions.
When a class is declared sealed, it cannot be inherited.
No! It can not be created as abstract classes cannot be declared sealed.
When you have a function defined in a class that you want to be implemented in an inherited class(es), you use virtual functions. The virtual functions could be implemented differently in different inherited class and the call to these functions will be decided at runtime.
You can redefine or overload most of the built-in operators available in C#. Thus a programmer can use operators with user-defined types as well.
Overloaded operators are functions with special names the keyword operator followed by the symbol for the operator being defined. Similar to any other function, an overloaded operator has a return type and a parameter list.
n interface is defined as a syntactical contract that all the classes inheriting the interface should follow. The interface defines the 'what' part of the syntactical contract and the deriving classes define the 'how' part of the syntactical contract.
Interfaces define properties, methods, and events, which are the members of the interface. Interfaces contain only the declaration of the members. It is the responsibility of the deriving class to define the members. It often helps in providing a standard structure that the deriving classes would follow.
The preprocessor directives give instruction to the compiler to preprocess the information before actual compilation starts.
All preprocessor directives begin with #, and only white-space characters may appear before a preprocessor directive on a line. Preprocessor directives are not statements, so they do not end with a semicolon (;).
You can use the #if directive to create a conditional directive. Conditional directives are useful for testing a symbol or symbols to check if they evaluate to true. If they do evaluate to true, the compiler evaluates all the code between the #if and the next directive.
C# exceptions are represented by classes. The exception classes in C# are mainly directly or indirectly derived from the System.Exception class. Some of the exception classes derived from the System.Exception class are the System.ApplicationException and System.SystemException classes.
The System.ApplicationException class supports exceptions generated by application programs. Hence the exceptions defined by the programmers should derive from this class.
The System.SystemException class is the base class for all predefined system exception.

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