MELJUN CORTES VB.net_Visual Basic .NET Language

8/8/2019 MELJUN CORTES VB.net_Visual Basic .NET Language

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Visual Basic .NET Programming

Visual Basic .NET

Language

Data Types, Variables and Arrays

Operators, Conditionals, and Loops

Procedures (Sub and Function)

Visual Basic .NET Language * Property of STI Page 1 of 64

Exception Handling


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Data

Types

The data type of a variable or constant

indicates what type of information will be

stored in the allocated memory space.

Each type has

a name (e.g., Integer) and

a size e. . 4 b tes


• size indicates the number of bytes each

object of this type occupies in memory


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TypeSize (in

bytes)Description

Boolean 2 True or false.

Byte 1 Unsigned (values 0-255).

Char 2Unicode characters (0-65,535

unsigned)

Date 8Midnight 1/1/0001 through

Data

Types


.

Decimal 16

Fixed-precision numbers up to 28digits and the position of the

decimal point; typically used infinancial calculations; requiresthe suffix "m" or "M."

Double 8

Double-precision floating-pointnumbers; holds the valuesfrom approximately +/-5.0 *10-324 to approximately +/-1.8* 10308 with 15-16 significantfigures.


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Data

Types

TypeSize (in

bytes)Description

Integer 4

Integer values between -

2,147,483,648 and2,147,483,647.

Long 8

Integers ranging from -9,223,372,036,854,775,808to


9,223,372,036,854,775,807.

Short 2 Integer values -32,768 to 32,767.

Single 4

Floating-point numbers; holdsthe values fromapproximately +/-1.5 * 10-45

to approximate +/-3.4 * 1038

with 7 significant figures.

String VariesA sequence of Unicode

characters.


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Data Types

Changes

Visual Basic

6.0Visual Basic .NET

Integer Short

Long Integer

(none) Long


Changes to Existing Data Types

Variant Not supported: use Object

Currency Not supported: use Decimal

Date No longer stored as a Double

String (fixed

length)Not supported


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CType

Use the CType function to convert any

value from one data type to another.

Similar to CStr and CInt in VB 6.0.

Syntax:

CType (expression, typename)


Example:

Dim strX as String, intY as

Integer

strX=“34”

intY=CType(strX, Integer)


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Variables

A variable is an object that can hold a

value.

A variable is a named storage location

(i.e., stored in memory) with a type.

Declaring and Initializing Variable


yn ax:

Dim Identifier [As DataType] =value/expression

Example:

Dim i As Integer = 15

Dim dToday As Date = Now()


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Variable

Defaults

If variables are not initialized, it will

have the default value based on the

type of variable assigned as type.

Datatype Default value


Boolean FALSE

Date 01/01/0001 12:00:00 AM

Object Nothing

String Nothing

Default values for uninitialized variables


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Variable

Scope

Variable scope can be declared as

Private

Public


Shared

Protected

Friend


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Constants

A constant is like a variable that can store

a value, but it cannot be changed while

the program runs.

Declaring Constant


=

expression

Example:

Const consX as Integer = 100


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Arrays

Array is a memory location that is used to

store multiple values.

An array is an indexed collection of

objects, all of the same type (e.g., all

integers, all strings, etc.).


It is the simplest collection of objects in

VB.NET.


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Types of

Arrays One-dimensional arrays

with element identified by a single

subscript

Multidimensional arrays

allows you to create rows of elements, oneabove the other


• Rectangular

– all the rows are of the same

length

• Jagged

– each row has different length


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Declaring

an Array

Declaring one-dimensional array

Dim Array_Name (Num_Elements)

[As Element_Type]

where


Array_Name – name of the array

Num_Elements – number of elements the

array can containElement_Type – data type of elements

Example:

Dim aryEmp_Name(100) as String


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Declaring

an Array

Declaring multidimensional array

Dim Array_Name ( , ) [As

Element_Type]

A two-dimensional array has two indices.


The number of dimension in an array is

called the rank of an array.

Example:

Dim arr(10,2) as String


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Dynamic

Arrays

The size of a dynamic array can vary

during the execution of the program.

Creating dynamic array

use Dim statement, declaring it with empty


Dim arr_Name() as String


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ReDim

Statement

Use ReDim statement to specify or change

the size of one or more dimensions of an

array that has already been declared.

Syntax:


_


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Preserve

Keyword

Use the Preserve keyword with the ReDim

statement. It copies the elements of the

old array to the new one before modifying

the dimension of the array.

Dim arr_Name() as String

ReDim Preserve arr_Name(100)



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Visual Basic

Operators

The arithmetic operators are as follows:

^ Exponentiation

* Multiplication

/ Division

\ Integer division


Mod Modulus

+ Addition

- Subtraction

>> right shift on a bit pattern


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Visual Basic

Operators

The assignment operators are as follows:

= Assignment

^= Exponentiation followed by

assignment

*= Multiplication followed by


/= Division followed by

assignment \= Integer division followed by

assignment

+= Addition followed by

assignment

-= Subtraction followed by

assignment &= String concatenation

followed by assignment


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Visual Basic

Operators

The comparison operators are as follows:

< Less than

Greater than

>= Greater than or equal to

=


Not equal to

Is True if two object references

refer to the same object

Like Performs string pattern

matching


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Visual Basic

Operators

The string concatenation operators are as

follows:

& String concatenation

+ String concatenation



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Visual Basic

Operators

The logical/bitwise operators are as

follows:

And Performs an “And” operation

Not Reverses the logical value of

its operand, from true to false

and false to true.


Or Performs an “Or” operation.

Xor Performs an “Exclusive Or”

operation. AndAlso A “short-circuited” And

operator.

OrElse A “short-circuited” Or operator.


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Visual Basic

Operators

Other operators are as follows:

AddressOf Gets the address of a

procedure


GetType Gets information

about a type


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Visual Basic

Operators Operator Precedence

predetermined order to which the

operations occurred in an expression at

once is evaluated

Arithmetic and Concatenation

• Ex onentiation ^


• Negation (-)

• Multiplication and division (*,/)

• Integer division (\)• Modulus arithmetic (Mod)

• Addition and subtraction (+,-)

• String concatenation (+)

• String concatenation (&)

• Arithmetic bit shift ()


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Visual Basic

Operators Operator Precedence (con’t)

Comparison

• Equality (=)

• Inequality ()

• Less than, greater than ()

• Greater than or equal to (>=)

• Less than or equal to (


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Visual Basic

Operators Operator Precedence Example:

Dim intScore1, intScore2,

intScore3, _

intNumberStudents As Integer

intScore1 = 50

intScore2 = 60


intNumberStudents = 3

Console.WriteLine(“Average

grade = “ & _

intScore1 + intScore2 +

intScore3 / intNumberStudents)

Console.WriteLine (“Press

enter to continue…”)

Console.ReadLine ()


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Conditional

Statements also known as branching statements

allows a programmer to make decisions

and take different paths in the code

If statement


Se ect statement


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If

Statements

Making Decisions with If Statements

If condition Then

[statements]

ElseIf condition-1 Then

[statements-1]


.

.

.

ElseIf condition-n Then

[statements-n]

Else

[else statements]

End If


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If

Statements

Example:

Dim intQtyOrdered as Integer = 10

Dim dblDiscount as Double = 0

If intQtyOrdered


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Select

Statements

Making Decisions with Select Statements

Select Case test-expression

Case expression-1

[statement-1]

Case expression-2

-


.

.

.

Case expression-n

[statement-n]

Case Else

[else-statement]

End Select


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Select

Statements Example:

Dim strMonth as String

strMonth = InputBox(“Type name of

the month”)Select Case strMonth

Case “January”

MessageBox.Show(“Month of


JANUARY”)

Case “February”

MessageBox.Show(“Month ofFEBRUARY”)

.

.

Case “December”

MessageBox.Show(“Month of

DECEMBER”)Case Else

MessageBox.Show(“Incorrect

Month”)

End If


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Control

Statements also known as looping

repeat action(s) for a number of times or

until a specified condition is reached

For/Next statement


For Each/Next statement

Do/Loop statement

While/End statement

With statement


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For…Next

Statements

Using the For…Next Loop

For index [As dataType] = start To

end

[statements]

[Exit For]

[statements]


Next [index ]

Example:

For intCtr As Integer = 0 To 10

MessageBox.Show(“Counter is “ &

intCtr)

Next intCtr


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For Each…Next

Statements

Using the For Each…Next Loop

For Each element [As dataType] In

group

[statements]

[Exit For]

[statements]


Next [element]

Example:

Dim arrDays() as String =

(“Mon”,”Tue”,”Wed”,”Thu”,”Fri”)

For Each strElem As String in

arrDays

MessageBox.Show(strElem)

Next


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Do…Loop

Statements

Using the Do…Loop

Do [While | Until] condition

[statement]

Exit Do

[statements]


Or

Do

[statement]

Exit Do

[statements]

Loop [While | Until] condition


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Do…Loop

Statements

Example:

Dim intCtr as Integer = 1

Do While intCtr


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While…End While

Statements

Using the While Loop

While condition

[statement]

End While


Dim intCtr as Integer = 1While intCtr


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With

Statements

Using the With Statement

With object

[statements]

End With


With TextBox1.Height = 50

.Width = 500

.Text = “Enter value here”

End With


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Procedures

contain all of the executable code in the

application

gives the ability to logically group code

that will perform certain task



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Procedure

access modifiers

Access Modifiers determine the scope

within which a procedure can be called

Public

Private


Shared

Protected

Friend

Protected Friend


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Advantages of

Procedures

code in a procedure is reusable

application is easier to debug and

maintain



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Types of

Procedures

Sub Procedure

performs specific tasks

does not return a value to a calling

statement

Function Procedure


returns a value to a calling statement


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Sub

Procedure

The syntax for creating a Sub procedure

is:

[ ] [ {Overloads |Overrides | Overridable |

NotOverridable | MustOverride |

Shadows | Shared }]


Pu c | Protecte | Fr en |

Protected Friend | Private }]

Sub SubName [(arglist)]

[statements]

[Exit Sub]

[statements]

End Sub

The syntax for calling a Sub procedure is:

[ Call ]

([Arguments list])


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Sub

Procedure

Example:

Public Sub ComputeTotalAmount(ByVal

dblQty _ As Double, ByValdblPrice As Double)

Dim dblAmount As Double

dblAmount = dblQty * dblPrice


Console.Writeline(dblAmount)

End Sub

‘calling the sub procedure

Sub Main()

Call ComputeTotalAmount(10, 50)

End Sub


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Function

Procedures

The syntax for creating a Function

procedure is:

[][{Overloads | Overrides

| Overridable |NotOverridable | MustOverride |

Shadows | Shared }]

[{ Public | Protected | Friend |


ro ec e r en r va e

Function functionName [(arglist)]

[As type]

[statements]

[Exit Function]

[statements]

End Function

The syntax for calling a Function

procedure is:

ReturnValue =

([Arguments list])


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Function

Procedure

Example:

Public Function

GetTotalAmount(ByVal dblQty

As Double, ByVal dblPrice As

Double) As Double



dblAmount = dblQty * dblPrice

Console.Writeline(dblAmount)

Return dblAmountEnd Sub

‘calling the function procedure

Sub Main()


dblAmount = GetTotalAmount (10,50)

End Sub


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Built-in

Functions

The following are the built-in functions in

Microsoft.VisualBasic Namespace:

Microsoft.VisualBasic.Conversion

ErrorToString


Hex

Oct

Str

Val


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Built-in

Functions

Microsoft.VisualBasic.DateAndTime

DateAdd

DateDiff

DatePart

DateSerial


DateValue

Day

Hour

Minute

Month

MonthName

Now

Second

TimeOfDay

Timer


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Built-in

Functions

Microsoft.VisualBasic.DateAndTime

TimeSerial

TimeString

TimeValue

Today


WeekDayName

Year


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Built-in

Functions

Microsoft.VisualBasic.String

ASC

Chr

Filter

FormatNumber, FormatCurrency and

FormatPercent


FormatDateTime

GetChar

InStr

InStrRev

Join

LCase

Left

Len

LSet, RSet

LTrim,Trim,RTrim


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Built-in

Functions

Microsoft.VisualBasic.String

Mid

Replace

Space

Split


StrConv

StrReverse

UCase


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Exception

Handling

Visual Basic .NET has good support in

handling runtime errors or exceptions

ways of Handling Exceptions

Unstructured – centers on the


n rror o o s a emen

Structured – centers on the Try/Catchstatement


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Types of

Errors

Syntax Errors

due to misspelled keywords or variables

Logic Errors

code does not act expected


Runtime Errors

due to unhandled unexpected error


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Unstructured

Exception Handling

Unstructured exception handling revolves

around the

On Error GoTo statement

On Error {GoTo [ line |0|-1]|

Resume Next }


GoTo line – calls the error-handling

codes that starts at the line specified at

line

GoTo 0 – disables the enabled error

handler in the current procedure

GoTo -1 – disables the enabled error

handler in the current procedure

Resume Next – specifies that when an

exception occurs, execution skips over thestatement that caused the problem and

goes to the statement immediately

following


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Unstructured

Exception Handling

Example:

Private Sub GetName()

On ErrorGoTo errHandler

[code]

Exit Sub


‘Handle error

End Sub


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Exception’s Number

and Description

a built in error object named Err has a

Number property that determines an

error’s number

when testing the program, useErr.Number to determine the number of

errors that ma occur and use those


numbers to handle errors in different ways


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Resume

Statement

resumes program execution in

unstructured exception handling

Syntax:

Resume [0]

Resume Next


Resume resumes execution with thestatement that caused the error.

Resume Next resumes execution with the

statement after the one that caused the

error

Resume line resumes execution at line,

a line number or label that specifies where

to resume execution


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Resume

Statement

Example:

Private Sub DeleteAndCopyFile()

On Error Resume Next

If Dir(“C:\file.txt”)

“ “ Then

Kill(“C:\file.txt”)


If Err.Number 0 Then

Err.Clear()

End If

FileCopy(“E:\File.txt”,”

C:\file.txt”)

If Err.Number 0 Then

MsgBox(“Cannot Copy File,

Please Try Again”)

End IfEnd Sub


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Structured

Exception Handling

centers on the Try/Catch statement

advantages

supported by multiple languages

allows to create protective blocks of code


a ows er ng o excep ons s m ar oSelect Case statement

allows nested handling

code is easier to read, debug and maintain


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Try…Catch…

Finally

Syntax:

Try

[ tryStatements ]

[Catch [ exception1 [ As type1 ] ]

[ When expression1 ]

catchStatements1


[Catch [ exception2 [ As type2 ] ]

[ When expression2 ]

catchStatements2

[Exit Try]

.

.

[Catch [ exceptionn [ As typen ] ]

[ When expressionn ]

catchStatementsn

[Exit Try]

[Finally

[finally Statements] ]

End Try


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Try…Catch…

Finally

Parts of the syntax are:

Try – starts the try block

tryStatements – specifies the sensitive

statements where possible exceptions are

anticipated

Catch – starts the block that handles the


exception(s)

exception – specifies the variable given

to the exception type – indicates the type of the exception

wanted to catch in a Catch block

When expression – specifies a Catch

block clause that means the Catch block

will catch exceptions only when expression

is True


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Try…Catch…

Finally

Parts of the syntax are:

catchStatements – specifies statements

that handle exceptions occurring in the Tryblock

Exit Try – exists a Try/Catch statement

immediately.


Finally – starts a Finally block that is

always executed when execution leaves

the Try/Catch statement finallyStatements - specifies

statements that are executed after all

other exception processing has occurred


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Try…Catch…

Finally

Example:

Sub TrySimpleException

Dim i1, i2, iResult As Decimali1 = 21

i2 = 0

Try


Result = 1 2 Cause

divide-by-zero error

MsgBox (iResilt) ‘ Will not

execute

Catch eException As Exception

‘ Catch the exception

MsgBox (eException.Message)

‘ Will not execute

Finally

Beep

End Try

End Sub


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System.Exception

Class

Property ormethod

Information provided

Message property why the exception was

thrown

provides information about a particular

exception

Source property the name of the application

or object that generated the

exceptionStackTraceproperty

exception history

InnerExceptionproperty

for nested exceptions

HelpLink property the appropriate Help file,

URN, or URLToString method the name of the exception

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MELJUN CORTES VB.net_Visual Basic .NET Language