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VB.Net

What is it?

  • ASP.NET is an open source web application framework created by Microsoft.

  • It allows programmers to develop dynamic websites and web services.

  • It provides integration of HTML, CSS and JavaScript.

History

  • First released in January 2002. 

  • Developed by Microsoft.

  • Successor of Active Server Page (ASP)

Configure VB.Net

Environment Setup

  • First released in January 2002. 

  • Developed by Microsoft.

  • Successor of Active Server Page (ASP)

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The Hello World

  • First released in January 2002. 

  • Developed by Microsoft.

  • Successor of Active Server Page (ASP)

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Basics of VB

  • VB.Net is an object-oriented programming language. 

  • Class

  • Instance 

  • Methode

  • Instance Variable

Class

  • Class is a Blueprint of object.

  • Class means, it can have logic, which can be instantiated.

  • All the methods & variables inside a class are members.

  • We declare class with keyword Class ClassName, then members & and ends with End Class.

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Constructors & Destructors

Constructor

  • It is a sub, Declared as Sub New( ), then statement & End Sub.

  • Executed when an object is created.

  • It can have a parameter passed while instantiation.

Destructor

  • It is a sub, executed when the object of a class goes out of scope.

  • Declared as Sub Finalize( ), then statement & End Sub.

  • It can't contain parameters, executed at last.

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Methods

  • Shared methods or static methods can be invoked without creating an object of the class.

  • Instance methods are invoked through an object of the class

  • Sub Main ( ) is the Entry of a Program.

  • Declaring inside Class, Public Shared Sub Main( )

  • Declaring inside Module, Public Sub Main( )

Identifiers

  • The identifier is a name used to name a Class, Module, Function, Variable etc.

  • Here is some rules:

    • It must starts with leter

    • Can contin numbers (0 - 9)

    • Can have (_)

    • Can not have these characters : ? - +! @ # % ^ & * ( ) [ ] { } . ; : " ' / and \​

    • Should not be Reserved Keyword

Datatypes

  • Data types refer to an extensive system used for declaring variables or functions of different types.

  • VB have wide range of Datatypes: 

    • Boolean​

    • Byte

    • Char

    • Date

    • Decimal

    • Double

    • Integer

    • Long

    • Object

    • SByte

    • Short

    • Single

    • String

    • UInteger

    • ULong

    • UShort

    • User-Defined datatype

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Type Conversion Function

  • There are some predefined functions for converting one datatype to another datatype.

  • Here are some example out of 16 conversion function.:

    • CInt (expression)​  - Convert to Integer datatype

    • Clng (expression) - Convert to long datatype

    • CUShort(expression)

    • CBool(expression)

    • CBool(expression)

    • CObj(expression)

    • etc

Variable

  • A variable is nothing but a name given to a storage area that our programs can manipulate. 

  • The Dim statement is used to declare a variable.

Access Modifier

  • Access modifiers decide accessibility of your class or class member.

  • There are 5 access modifier in VB.Net

Access modifier

Public

Private

  • Applicable only to the members of a type. 

  • Accessible inside the class.

  • Classes and class members marked with Public 

Protected

  • Private but can be inherited.

  • Applicable to class and members.

Friend

  • Available only inside the project.

  • Applicable to class and members.

Protected friend

  • Access to the same project.

  • And can be inherited 

Accepting Value from User

  • The Console class in System namespace provides a function ReadLine for accepting input from user.

  • Here is a program asking Name and Age, and prints out a sentence.

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Compiling .vb file

Executing .exe file

Asks user input & Prints a sentence.

Constant in VB

  • Constant refers to a fixed value in a program which can not be altered.

  • With Const keyword, we can declare the constant value.

  • Here are some constant value for printing & display in Visual Basic.

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  • Enum

  • An enumeration type is declared by Enum statement. 

  • It is a an Integer type by default.

  • We can change using As Datatype while declaring.

  • The defined value can be used at Class, Module, Structure, procedure or block level.

Compiler Directives

  • These directives give instructions to compiler to preprocess the information before actual Compilation starts.

  • Follwoings are some directives:

    • #Const Directives

    • #ExterialSource Directive

    • #IF... THAN... #ELSE Directives

    • #Region Directive

Inheritance

  • All the properties & methods of a Class/Interface can be reused by a Class

  • Parent class is called Base Class, where members are declared.

  • Child class is called Derived Class, where we can access those members.

  • Syntax of declaring Derived Class: Class cName : Inherits BaseClassName

  • Protected DIm a 

  • Protected Dim b

  • Public Sub Abc()

Base Class

: Inherits

  • Uses those Members fof Base Class

  • Can overide Sub

  • Can have more Mebers

Derived Class

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Conditional Statement:

  • These are the decision-making statements on the conditions.

  • Here are 3 conditonal statements:

    • IF  ELSE

    • SELECT CASE​

    • Nested IF, Select

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Conditional Loops:

  • The block of code keeps executed when the condition is TRUE.

  • Iterates the block of code some specific loop.

  •  Below is the Loop Syntax:

Do Loop

  • Do While (condition)... Loop

  • Do... Loop While (condition)

  • Do Until (condition)... Loop

  • Do... Loop Until (condition) Loop 

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While

  • Here the block code executed while the condition is TRUE.

  • Syntax: While condition ...  End While

For Next

  • It iterates the code for a specified number of times.

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For Each

  • For an iteration of Array or Collection elements we use For Each loop.E

  • Syntax: For Each elementVar In arrayName ... Next

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With Object

  • It is not a loop.

  • It executes a block of statements that refer to a common object/reference.

  • Syntax: With obj ... End With

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Loop Control Statement

  • It changes the execution from a loop.

  • Here are 3 conditional statements:

    • Exit for/ while: Terminates the loop

    • Continue for/while: Skip the remainder of the body, continue to re-iterate.

    • GoTo line1: Transfers control the labeled statement.

Collection

  • Collection stores a wide range of data.

  • Unlike Array, it can store different datatypes.

  • Memory size allocates as it contains elements.

Types of Collection

  • All classes are belongs to System.Collections namespace.

  • Here are some collection classes.

System.Collection

ArrayList

HashTable

Queue

Stack

ArrayList

  • Stores index bases elements.

  • Unsorted elements access.

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HashTable

  • It contains Key & value pair.

  • We can access keys & values.

  • It order to access keys, it needs to call ht.Keys which is ICollection class type.

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Queue

  • Stores one value.

  • The first entered elements is being accessed in first. (FIFO)

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Stack

  • Here we access the element in Last in First Out  (LIFO) order.

  • It stores the elements like Stacks do; one after a

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String

  • An array of characters.

  • An object of Stystem.String class.

  • Can declare as String.

Creation of String

  • A string can be created by following ways:

By String literal

Dim var as String = "Stone"

Using String Class Constructor

var = new String (charArray)

Ways of

creating String:

Property of Method returns String datatype

var = String.Join(" , ", stringArray)

By formatting method, which converts object to String type

var = String.Format("{0:t}", dateTime)

  • The below program shows Declaring and Creating String.

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String Methods:

  • String class has some Properties & methods given below for string manipulation.

  • Here is 2 properties of String class:

    • string1.Chars( 2 ): Returns char at a specified index.

    • string1.Length( ): Gets the length of a string.​​​

  • Below table has some static and non-static String method with description:

Array:

  • Is used to store a collection of data of the same datatype.

  • We can store/access from an index of a collection.

  • We declare an array by variable followed by ( ) or (size).

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  • Array Class is defined on System namespace.

  • It has some properties & methods for manipulating the array object.​

Array Properties:

  • arr1. IsReadOnly : Returns True if Read only

  • arr1. Length : Returns array length

  • arr1. Rank : Returns which dimension

Array Methods:

  • Array class has some static and non-static methods handle the array.

  • Static methods can be called by Array. and method name.

  • A non-static method can be called by arrayObject. and method name.

Collection:

  • Is used to store a collection of data of the same datatype.

  • We can store/access from an index of a collection.

  • We declare an array by variable followed by ( ) or (size).

Programs

Program 1

  • Find the  First non-repeated characher in a String.

  • Input: stoneprofits

  • Output: n

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Program 2

  • Find Permutation of a Sting.

  • Input: ab

  • Output: ab, ab

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Program 3

  • Find Digit Identification if string have any number.

  • Input: stone123profits

  • Output: TRUE, it contains number.

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  • We checked here, with 2 string; one with number and another without number.

  • Here is the result shown in command prompt.

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Program 4

  • Find & Replace the 1st highest repeated character with user given value.

  • Input: abcabab

  • Output: pbcpbpb

  • The output on Command Prompt looks like below.

Program 5

  • WAP to print a Numbered Diamond.

  • Input: 5

  • Output: -

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  • The Diamond output is here.

  • It asks a number as user input for make a diamond.

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Program 6

  • WAP to sum the numbers in a String.

  • Input: stone123profits7

  • Output: 130

File Handle in VB

  • File is a collection of data stored in disk.

  • In VB.Net we can pass the data through a communication path called stream.

  • There are lot of classes in System.IO availble for accessing Files.

Read File

  • There is StreamReader class is used to read text files.

  • This class inherits TextReader & Stream abstract classes.

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Write File

  • We used StreamWriter class for writting a text file.

  • A array of strings is created, then we inserted data to file object with a string array loop.

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Exception Handling

  • An exception is an unwanted error which breaks the execution flow of a program.

  • To continue the flow of execution, we can keep the codes in a block is called Exception Handling.

  • Here we can transfer the control from one part of a program to another, using this keyword:

    • Try: Where exception raised.

    • Catch: If exception, exceptions are being handled here.Can have multiple catches.

    • Finally: Inside this block, codes are executed regardless of exception is raised.

    • Throw: A program throws an exception.

Exception Classes

  • VB.Net is an object-oriented programming language.

Hierarchy of Exception Classes

System.Exception

System.ApplicationException

ArithmeticException (DevidedByZeroException)

IndexOutOfBoundException

ArgumentException (ArgumentOutOfBoundException)

System.SystemException

(User-Defined Exception Classes)

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User-Defined Exception

  • In VB.Net, user can create an Costumized-Exception class, and thow this object.

  • To do so, the User-Defined Exception class must inherits ApplicationException class.

  • Here we called Base-Class constructor with message as string.

  • Thow the user object inside a condition using throw keyword.

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VB.Net & Database

  • An exception is an unwanted error which breaks the execution flow of a program.

  • To continue the flow of execution, we can keep the codes in a block is called Exception Handling.

  • Here we can transfer the control from one part of a program to another, using this keyword:

    • Try: Where exception raised.

    • Catch: If exception, exceptions are being handled here.Can have multiple catches.

    • Finally: Inside this block, codes are executed regardless of exception is raised.

    • Throw: A program throws an exception.

Connect with SQL Server

Step 1

  • Create a Connection object.

Step 2

  • Use SqlConnection object to open the connection.

Step 3

  • Create a command object.

Step 4

  • Create a SqlDataReader object to Retrieve the data from SQL server.

  • Execute the query & store the result in DataReader.

Step 5

  • Loop over the DataReader and display the data. 

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Database

Command Line

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