UNIT 1Introduction to Visual Basic programming

Unit Covered Introduction to visual studio

Variables:

Data type conversions, operators and its precedence, boxing

and un-boxing

Flow control in VB

Procedures: subroutines and functions.

Array.

Strings, StringBuilder and Enumerations

Exception handling in VB.NET

IDE Stands for Integrated Development Environment

Visual Studio is a powerful and customizable programming environment that contains all the tools you need to build programs quickly and efficiently.

It offers a set of tools that help you – To write and modify the code for your programs

– Detect and correct errors in your programs.

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IDE cont…

It includes1. Menu Bar2. Standard Toolbar3. Toolbox4. Forms Designer5. Output Window6. Solution Explorer7. Properties Window8. Server Explorer

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What is DataType?

In a programming language describes that what type of data a variable can hold .

When we declare a variable, we have to tell the

compiler about what type of the data the variable can hold or which data type the variable belongs to.

What is Variable?

Variables are used to store data. Symbolic names given to values stored in memory and

declared with the Dim keyword Dim stands for Dimension.

constants– The same as variables, except that constants are

assigned a value that cannot then be altered.

How to declare Variable? Syntax :

Dim VariableName as DataTypeVariableName : the variable we declare for hold the

values.DataType : The type of data that the variable can

hold Example :

Dim count as Integer count : is the variable nameInteger : is the data type

List of Data typesType Storage size Value range

Boolean 2 bytes True or False

Byte 1 byte 0 to 255 (unsigned)

Char 2 bytes 0 to 65535 (unsigned)

Date 8 bytes January 1, 0001 to December 31, 9999

Decimal 16 bytes +/-79,228,162,514,264,337,593,543,950,335 with no decimal point;

Double 8 bytes -1.79769313486231E+308 to -4.94065645841247E-324 for negative values; 4.94065645841247E-324 to .79769313486231E+308 for positive values

Integer 4 bytes -2,147,483,648 to 2,147,483,647

List of Data typesType Storage

size Value range

Long 8 bytes -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

Object 4 bytes Any type can be stored in a variable of type Object

Short 2 bytes -32,768 to 32,767

Single 4 bytes -3.402823E to -1.401298E-45 for negative values; 1.401298E-45 to 3.402823E for positive values

String Depends on platform

0 to approximately 2 billion Unicode characters

User-Defined Type (structure)

Sum of the sizes of its members. Each member of the structure has a range determined by its data type and independent of the ranges of the other members

Access Specifiers Public: Gives variable public access which means that

there is no restriction on their accessibility

Private: Gives variable private access which means that they are accessible only within their declaration content

Protected: Protected access gives a variable accessibility within their own class or a class derived from that class

Friend: Gives variable friend access which means that they are accessible within the program that contains their declaration

Access Specifiers

Protected Friend: Gives a variable both protected and friend access

Static: Makes a variable static which means that the variable will hold the value even the procedure in which they are declared ends

Shared: Declares a variable that can be shared across many instances and which is not associated with a specific instance of a class or structure

ReadOnly: Makes a variable only to be read and cannot be written

Scope of Variable Scope : Element's scope is its accessibility in your code.

Block scope —available only within the code block in which it is declared

Procedure scope —available only within the procedure in which it is declared

Module scope —available to all code within the module, class, or structure in which it is declared

Namespace scope —available to all code in the namespace

Option Statement

The Option statement is used to set a number of options for the code to prevent syntax and logical errors.

This statement is normally the first line of the code.

The Option values in Visual Basic are as follows.

– Option Explicit

– Option Strict

– Option Compare

Option Explicit Option Explicit

– Set to On or Off

– Default : On

– This requires to declare all the variables before they

are used.

Option Explicit

If Option Explicit mode in ON , – have to declare all the variable before you use it in

the program . If the Option Explicit mode is OFF

– VB.Net automatically create a variable whenever it sees a variable without proper declaration.

CODE

Option Strict

Option Strict– Set to On or Off.– Default : off– Used normally when working with conversions in

code.– Option Strict is prevents program from automatic

variable conversions, that is implicit data type conversions .

Option Strict

– If Option is on and you assign a value of one type to a variable of another type Visual Basic will consider error.

– There is any possibility of data loss, as when you're trying to assign the value in a variable to a variable of less precise data storage capacity.

– In that case, you must use explicit conversion.

CODE

Option Compare

Default : Binary. Binary - Optional - compares based on binary

representation - case sensitive Text - Optional - compares based on text representation

- case insensitive

Code

Type Conversion

In Visual Basic, data can be converted in two ways: – Implicitly (widening), which means the conversion

is performed automatically, – Explicitly(narrowing), which means you must

perform the conversion.

Implicit Conversions (widening Conversion)

Widening conversion is one where the new data is

always big enough to hold the old datatype’s value.

For example

– Long is big enough to hold any integer.

– Copying an integer value in to long variable is widening

conversion.

Example

Module Module1Sub Main()

Dim d=132.31223 as DoubleDim i as Integer

i=5i=d

d=iConsole.WriteLine("Integer value is" & i)

End SubEnd Module

Explicit Conversions (Narrowing Conversion)

– When types cannot be implicitly converted you should convert them explicitly.

– This conversion is also called as cast.– Explicit conversions are accomplished using CType

function.

i = CType(d, Integer)

or i=CInt(d)

Code

ExampleModule Module1 Sub Main() Dim d As Double d = 132.31223 Dim i As Integer i = CType(d, Integer) 'two arguments, type we are converting

'from, to type desired Console.WriteLine("Integer value is " & i) Console.ReadKey() End SubEnd Module

CTypeBelow is the list of conversion functions which we can use in VB .NET.

CBool— Convert to Bool data type. CByte— Convert to Byte data type. CChar— Convert to Char data type. CDate— Convert to Date data type. CDbl— Convert to Double data type. CDec— Convert to Decimal data type. CInt— Convert to Int data type. CLng— Convert to Long data type. CObj— Convert to Object type. CShort— Convert to Short data type. CSng— Convert to Single data type. CStr— Convert to String type.

Operators

An operator is a symbol used to perform operation on one or more operands.

SyntaxOper1=oper2 operator oper3

ExampleSum=a+b

Operators Arithmetic OperatorsOperator Use

^ Exponentiation

-Negation (used to reverse the sign of the given value, exp -intValue)

* Multiplication

/ Division

\ Integer Division

Mod Modulus Arithmetic

+ Addition

- Subtraction

Operators

Concatenation Operators

Operator Use

+ String Concatenation

& String Concatenation

Difference

Preview

/ operator \ operator

It is used for Division It is used for Integer Division

e.g. Dim a As Integer a = 19 / 5

Result : 4

e.g. Dim a As Integer a = 19 \ 5

Result : 3

Operators Comparison Operators

Operator Use

= Equality

<> Inequality

< Less than

> Greater than

>= Greater than or equal to

<= Less than or equal to

Operators Logical / Bitwise Operators

Operator Use

Not Negation

And Conjunction

AndAlso Conjunction

Or Disjunction

OrElse Disjunction

Xor Disjunction

Operator Precedence1. Arithmetic operators have the highest precedence and

are arranged this way, from highest precedence to lowest:– Exponentiation (^)– Negation (-) (for example, -intValue reverses the sign of the

value in intValue)– Multiplication and division (*, /)– Integer division (\)– Modulus arithmetic (Mod)– Addition and subtraction (+,-)

2. Concatenation operators:– String concatenation (+)– String concatenation (&)

Operator Precedence3. Comparison operators, which all have the same

precedence and are evaluated from left to right– Equality (=)– Inequality (<>)– Less than, greater than (<,>)– Greater than or equal to (>=)– Less than or equal to (<=)

4. Logical/Bitwise operators, which have this precedence order, from highest to lowest:– Negation-(Not)– Conjunction-(And,AndAlso)– Disjunction-(Or, OrElse, Xor)

Flow control in VB:

Conditional Statement

Selection statement

Iteration statement

jump statement

Conditional Statements If....Else statement Syntax

If condition Then[statements]

Else If condition Then[statements]

--Else

[statements]End If

Example

Module Module1 Sub Main() Dim a,b As Integer If a=b Then Console.WriteLine(“a equal to b”) ElseIf a<b Then Console.WriteLine(“a less than b")

Else Console.WriteLine(" a greater than b") End If

Console.ReadKey() End SubEnd Module

Select....Case Statement

It is used to avoid long chains of If….Then….ElseIf statement.

It compare one specific variable against several constant expressions then we use select….case statement.

Select Statements The syntax of the Select Case statement

Select Case test_expression

Case expressionlist-1

        statements-1  

Case expressionlist-n

        statements-n. . .

 Case Else

else_statements

End Select

Example

Module Module1 Sub Main() Dim i As Integer Console.WriteLine("Enter a number between 1 and 4") i = Val(Console.ReadLine()) Select Case i Case 1 Console.WriteLine("You entered 1") Case 2 Console.WriteLine("You entered 2")

Case Else Console.WriteLine("You entered >2")

End Select Console.ReadKey() End SubEnd Module

Iteration StatementFor Loop The For loop in VB .NET needs a loop index which counts the

number of loop iterations as the loop executes. The syntax for the For loop looks like this:

For index=start to end [Step stepvalue]

[statements]

Next[index]

Example

Module Module1 Sub Main()

Dim d As IntegerFor d = 0 To 2Console.WriteLine("In the For Loop")Next d

End SubEnd Module

While loop

It runs set of statements as long as the conditions specified with while loop is true.

The syntax of while loop looks like this:

While condition

[statements]

End While

ExampleModule Module1 OUTPUT

Sub Main()Dim d, e As Integerd = 0e = 6While e > 4

e -= 1d += 1

End WhileConsole.WriteLine("The Loop run " & e &

"times")End Sub

End Module

Do Loop

Do[{while | Until} condition][statements][Exit Do][statements]

Loop

The Do loop can be used to execute a fixed block of statements indefinite number of times.

The Do loop keeps executing it's statements while or until the condition is true.

The syntax of Do loop looks like this:

Do[statements][Exit Do][statements]

Loop [{while | Until} condition]

Example

Module Module1 Output Sub Main() Dim str As String Console.WriteLine("What to do?") str = Console.ReadLine() Do Until str = "Cool" Console.WriteLine("What to do?") str = Console.ReadLine() Loop Console.ReadKey() End SubEnd Module

Example

Write a console application to find out n!.(use for loop)

Write a console application to find out sum of the digits.

– i.e. 1237 : 1+2+3+7 = 13.(using while condition)

Write a program to enter marks of student and calculate grade of the student.

Procedure

They are a series of statements that are executed when

called.

There are two types of procedure in VB .NET:

– Function : Those that return a value.

– Subroutines (Procedure) : Those that do not return

a value.

Sub Procedure

Sub procedures are methods which do not return a value.

Each time when the Sub procedure is called the statements within it are executed until the matching End Sub is encountered.

Sub Main(), the starting point of the program itself is a sub procedure.

Sub routine can be created in module and class.

Default access modifier is public.

Syntax

[{ Overloads | Overrides | Overridable | NotOverridable | MustOverride |

Shadows | Shared }]

[Access_Specifiers] Sub ProcedureName[(argument list)]

[ statements ]

[ Exit Sub ]

[ statements ]

End Sub

Code

Access_Specifiers : Public | Protected | Friend | Protected Friend | Private

Attribute List - List of attributes for this procedure. You separate multiple attributes with commas.

– ByVal : Pass by value

– ByRef : Pass by Reference.

Procedure Name: Name of the Procedure

Exit Sub : Explicitly exit a sub procedure.

Overloads : it indicates that there are other procedure in the class with the same name but with different argument.

Overrides :-Specifies that this Sub procedure overrides a procedure with the same name in a base class.

Overridable : -Specifies that this Sub procedure can be overridden by a procedure with the same name in a derived class.

NotOverridable:- Specifies that this Sub procedure may not be overridden in a derived class.

MustOverride:-Specifies that this Sub procedure is not implemented in class and must be implemented in a derived class.

Function

Function is a method which returns a value.

Functions are used to evaluate data, make calculations

or to transform data.

Functions are declared with the Function keyword.

Syntax

[{ Overloads | Overrides | Overridable | NotOverridable | MustOverride | Shadows | Shared }]

[Access_Specifiers] Function Func_name[argument List ]

[ As type ]

[ statements ]

[ Exit Function ]

[statements ]

End Function

Type- Data type of the value returned by the Function

procedure can be

– Boolean, Byte, Char, Date, Decimal, Double, Integer,

Long, Object, Short, Single, or String;

Access_Specifiers : Public | Protected | Friend |

Protected Friend | Private

Code

Example

The calculate_Amount sub routine takes the quantity and unit price of product and calculate the total amount.

The calculate_Amount sub routine takes the quantity and unit price of product and return total amount.

Array

It is a collection of elements of same datatype.

It access using single name and index number.

This is very useful when you are working on several

pieces of data that all have the same variable datatype &

purpose.

Type of Array Demo

One dimensionalDim Array_name(size) as Datatype

e. g. Dim name(20) As StringDim Array_name() as Datatype=new data type(size){list of constant separated by comma}

e.g. Dim num() as integer=New integer(5) {1,2,3,4,5}

Multidimensional

e. g. Dim matrix(3,3) As Integer Dim mat(,) as Integer=New Integer(3,3)

Dim matrix(,) As Integer =New Integer(){{2,2},{0,0},{1,3}}

Dynamic Array

You can resize an array using ReDim Keyword.

Syntax

ReDim [Preserve] Array_name(new Size)

If you use ReDim statement then existing content are erased.

If you want to preserve existing data when reinitializing an array then you should use the Preserve keyword .

Dim Test() as Integer={1,3,5}

'declares an array an initializes it with three members

ReDim Test(25)

'resizes the array and lost existing data.

ReDim Preserve Test(25)

'resizes the array and retains the data in elements 0 to 2

Demo

Function In Array

Function Description

GetLength Get length of the array

GetType Get Datatype of an array

First It gets the first element of an array.

Last It gets the last element of an array.

Max It gets the Maximum element of an array.

Min It gets the Minimum element of an array.

For Each……Next Loop

This element automatically loops over all the element in array or collection.

No need to write starting or ending index.Syntax

For Each element in group [statement]

[Exit For] [Statement]

Next [Element]

Example

DifferenceFor For Each

The for loop executes a statement or a block of statements repeatedly until a specified expression evaluates to false.  

The for Each statement repeats a group of embedded statements for each element in an array or an object collection.

Need to specify the loop bounds No not need to specify the loop bounds minimum or maximum

Syntax : For index=start to end [Step]

[statements][statements]

Next[index]

Syntax : For Each element in group [statement]

[Exit For] [Statement]

Next [Element]

DifferenceWhile Until

"do while" loops while the test case is true.

“do until ” loops while the test case is false.

Syntax : Do while condition

[statements][Exit Do]

[statements]Loop

Syntax : Do Until condition

[statements][Exit Do]

[statements]Loop

String Function Code

To Do This To USE

Concatenate two strings &, +, String.Concat, String.Join

Compare two strings

StrComp Return Zero if same else 1

String.Compare Return zero if same else 1

String.Equals Return true if same else false

String.CompareTo Return Zero if same else false

Convert strings CStr, String. ToString

Copying strings =, String.Copy

Convert to lowercase or uppercase

Lcase, Ucase,String. ToUpper, String. ToLower

String Function

To Do This To USE

Create an array of strings from one string

String.Split

Find length of a string Len, String.Length

Get a substring Mid, String.SubString

Insert a substring String.Insert

Remove text String.Remove

Replace text String.Replace

String Function

To Do This To USE

Search strings InStr, String.Chars, String.IndexOf, String.LastIndexOf,

Trim leading or trailing spaces (Remove Unwanted space)

LTrim, RTrim, Trim, String.Trim, String.TrimEnd, String.TrimStart

Work with character codes Asc, Chr

Enumeration

Access Modifier : (Optional) Public, Protected, Friend, Private

[ access modifier ]

Enum enumeration_name [ As data type ]

member list

End Enum

ExampleEnum Days Demo

Monday=1Tuesday=2Wednesday=3Thursday=4Friday=5Saturday=6Sunday=7

End EnumSub Main() Console.WriteLine(“Friday is a day” & Days.Friday)End Sub

Exception Exceptions : It is a runtime errors that occur when a

program is running and causes the program to abort

without execution.

Such kind of situations can be handled using Exception

Handling.

Exception Handling :

– By placing specific lines of code in the application we

can handle most of the errors that we may encounter

and we can enable the application to continue running.

VB .NET supports two ways to handle exceptions,

– Unstructured exception Handling

– using the On Error goto statement

– Structured exception handling

– using Try....Catch.....Finally

Unstructured Exception Handling

The On Error GoTo statement enables exception

handling and specifies the location of the exception-

handling code within a procedure.

How the On Error GoTo statement works:

On Error GoTo [ lable | 0 | -1 ] | Resume Next

Code

Statement Meaning

On Error GoTo -1 Resets Err object to Nothing, disabling error

handling in the routine

On Error GoTo 0 Resets last exception-handler location to

Nothing, disabling the exception.

On Error GoTo

<labelname>

Sets the specified label as the location of the

exception handler

On Error Resume

Next

Specifies that when an exception occurs,

execution skips over the statement that caused

the problem and goes to the statement

immediately following. Execution continues

from that point.

Structured Exception Handling

On Error Goto method of exception handling sets the

internal exception handler in Visual Basic.

It certainly doesn't add any structure to your code,

If your code extends over procedures and blocks, it can

be hard to figure out what exception handler is working

when.

Structured exception handling is based on a particular

statement, the Try…Catch…Finally statement, which is

divided into a

– Try block,

– optional Catch blocks,

– and an optional Finally block.

Syntax

Try

//code where exception occurs

Catch e as Exception

// handle exception

Finally

// final Statement

End Try

The Try block contains code where exceptions can occur. The Catch block contains code to handle the exceptions

that occur. If an exception occurs in the Try block, the code throws

the exception. It can be caught and handled by the appropriate Catch

statement. After the rest of the statement finishes, execution is

always passed to the Finally block, if there is one.

Code

Exception Object The Exception object provides information about any

encountered exception.

properties of the Exception object:

– HelpLink : can hold an URL that points the user to further information about the exception.

– InnerException : It returns an exception object representing an exception that was already in the process of being handled when the current exception was thrown.

– Message : It holds a string, which is the text

message that informs the user of the nature of the

error and the best way or ways to address it.

– StackTrace : It holds a stack trace, which you can

use to determine where in the code the error

occurred.

Standard ExceptionException Type Description

Exception Base type for all exceptions

IndexOutOfRangeException Thrown when you try to access an array index improperly

NullReferenceException Thrown when you try to access a null reference

InvalidOperationException Thrown when a class is in an invalid state

ArgumentException Thrown when you pass an invalid argument to a method

ArithmeticException Thrown for general arithmetic errors

Difference VALUE TYPE REFERENCE TYPE

Value type they are stored on stack

Reference type they are stored on heap

When passed as value type new copy is created and passed so changes to variable does not get reflected back

When passed as Reference type then reference of that variable is passed so changes to variable does get reflected back

Value type store real data Reference type store reference to the data.

Value type consists of primitive data types, structures, enumerations.

Reference type consists of class, array, interface, delegates

Value types derive from System.ValueType

Reference types derive from System.Object