VB.Net Introduction

Visual Studio 2012 Demo• Start page: New project/ Open project/Recent projects• Starting project:

• File/New Project/– C# /VB/Other language– Windows

» Windows form application– Project name/Project folder

• Project windows:– Form design view/Form code view– Solution Explorer

• View/Solution Explorer– ToolBox– Property Window

• Properties and Events– Server Explorer– Project/Add New Item– Property window example

Introduction to Visual Basic .Net

• Event-driven programming– The interface for a VB program consists of one

or more forms, containing one or more controls (screen objects).

– Form and controls have events that can respond to. Typical events include clicking a mouse button, type a character on the keyboard, changing a value, etc.

– Event procedure

Form

• Properties:– Name, FormBorderStyle, Text, BackColor,

BackImage, Opacity• Events:

– Load, FormClosing, FormClosed– GotFocus, LostFocus– MouseHover, Click, DoubleCLick

Common VB.Net Controls

• TextBox• Label• Button• CheckBox• RadioButton• ListBox• ComboBox• PictureBox

Text Box• Properties:

– AutoSize, BorderStyle, CauseValidation, Enabled, Locked, Multiline, PasswordChar, ReadOnly, ScrollBar, TabIndex, Text, Visible, WordWrap, etc.

• Properties can be set at the design time or at the run time using code.

• To refer to a property: – ControlName.PropertyName– Ex. TextBox1.Text– Note: The Text property is a string data type and

automatically inherits the properties and methods of the string data type.

Typical VB.Net Programming Tasks

• Creating the GUI elements that make up the application’s user interface.– Visualize the application.– Make a list of the controls needed.

• Setting the properties of the GUI elements• Writing procedures that respond to events

and perform other operations.

To Add an Event-Procedure• 1. Select the Properties window• 2. Click Events button• 3. Select the event and double-click it.

• Note: Every control has a default event. • Form: Load event • Button control: Click event• Textbox: Text Changed event

– To add the default event procedure, simply double-click the control.

Demo

FirstName

LastName

FullName

.Control properties

.Event: Click, MouseMove, Form Load, etc.

.Event proceduresFullName: textBox3.Text textBox3.Text = textBox1.Text + " " + textBox2.Text

Demo: Text alignment (TextBox3.TextAlign=HorizontalAlign.Center)TextBox3.BackColor=Color.Aqua

Demo

Num1

Num2

Sum =

.Control properties

.Event: Click, MouseMove, Form Load, etc.

.Event proceduresSum: textBox3.text=CStr(CDbl(textBox1.text)+CDbl(textBox2.text))Or (CDbl(textBox1.text)+CDbl(textBox2.text)).toString

Data Conversion Using VB Functions or .Net Methods

• VB functions: Cstr, Cdbl, …• .Net framework:

– System.Convert

• TextBox3.Text = (System.Convert.ToDouble(TextBox1.Text) + System.Convert.ToDouble(TextBox2.Text)).ToString

Configure VB Project• Project property page

– Application:• Target framework• Startup form

– Compile:• Target CPU• Option: explicit, strict, compare

– References• Tools/Options

– Environment

VB Defaults• Option Explicit:

– On --- must declare variables before use • Option Strict:

– Off --- VB will convert the data (implicit conversion)• Option Compare:

– Binary --- case sensitive– Text --- case insensitive

• Option Infer– On --- When you set Option Infer to On, you can declare variables

without explicitly stating a data type. The compiler infers the data type of a variable from the type of its initialization expression.

Variable Declarations• Option Explicit• Dim variableName as DataType• Variable naming rules:

– The first character must be a letter or an underscore character.

– Use only letters, digits, and underscore.– Cannot contain spaces or periods.– No VB keywords

• Naming conventions:– Descriptive– Consistent lower and upper case characters.

• Ex. Camel casing: lowerUpper, employeeName

Control Naming Conventions

• The first three letters should be a lowercase prefix that indicates the control’s type.– frm, txt, lbl, btn.

• The first letter after the prefix should be uppercase.– txtSalary, lblMessage

• The part of the control name after the prefix should describe the control’s purpose in the application.

VB Data Types• Boolean (True/False): 2 bytes• Byte: Holds a whole number from 0 to 255.• Char: single character• Date: date and time, 8 bytes.• Decimal: Real number up to 29 significant digits, 16 bytes• Double: real, 8 bytes• Single: real, 4 bytes• Integer: 4 bytes (int32, uint32)• Long: 8 bytes integer• Short: 2 bytes integer• String• Object: Holds a reference of an object

Variable Declaration Examples

• Dim empName as String• Declare multiple variables with one Dim:

– Dim empName, dependentName, empSSN as String • Dim X As Integer, Y As Single• Initiatialization

– Dim interestRate as Double = 0.0715

Variable Default Value

• Variables with a numeric data type: 0• Boolean variables: False• Date variables: 12:00:00 AM, January 1 of

the year 1.• String variables: Nothing

Arithmetic and String Operators

• Arithmetic operators:+, -, *, /. ^\ operator: Divides two numbers and returns an integer result.Mod: Divides two numbers and returns only the remainder.

• Example: 10 mod 3

.Net Math class:Math.Pow(2, 3)

• String Concatenation: &, +• Compound operator:

:X= X+1 or X +=1

Example

Dim dividend, divisor, quotient, remainder As Integer dividend = CInt(TextBox1.Text) divisor = CInt(TextBox2.Text) quotient = dividend \ divisor remainder = dividend Mod divisor TextBox3.Text = quotient TextBox4.Text = remainder

ToString

• MessageBox.Show("quotient is:" + quotient)– Trigger error

• MessageBox.Show("quotient is:" + quotient.ToString)• MessageBox.Show("Remainder is: " + remainder.ToString)• Option Strict

Change Machine to Return Smallest Number of Coins

Dim changes, quarters, dimes, nickles, pennies As Integer changes = CInt(TextBox1.Text) quarters = changes \ 25 dimes = (changes - quarters * 25) \ 10 nickles = (changes - quarters * 25 - dimes * 10) \ 5 pennies = changes - quarters * 25 - dimes * 10 - nickles * 5 TextBox2.Text = quarters TextBox3.Text = dimes TextBox4.Text = nickles TextBox5.Text = pennies

FV = PV * (1 +Rate) Year

Dim PV, Rate, Term, FV As Double PV = CDbl(TextBox1.Text) Rate = CDbl(TextBox2.Text) Term = CDbl(TextBox3.Text) FV = PV * (1 + Rate) ^ Term TextBox4.Text = FV.ToString("C")

Formatting Numbers with the ToString Method

• The ToString method can optionally format a number to appear in a specific way

• The following table lists the “format strings” and how they work with sample outputs

Format String

Description Number ToString() Result

“N” or “n” Number format 12.3 ToString(“n3”) 12.300

“F” or “f” Fixed-point scientific format 123456.0 ToString("f2") 123456.00

“E” or “e” Exponential scientific format 123456.0 ToString("e3") 1.235e+005

“C” or “c” Currency format -1234567.8 ToString("C") ($1,234,567.80)

“P” or “p” Percentage format .234 ToString("P") 23.40%

Data Conversion• Implicit conversion: When you assign a value of

one data type to a variable of another data type, VB attempts to convert the value being assigned to the data type of the variable if the OptionStrict is set to Off.

• Explicit conversion:– VB.Net Functions: CStr, Ccur, CDbl, Cint, CLng,

CSng, Cdate,Val, etc.– .Net System.Convert

• Type class’s methods:– toString

Date Data Type

• Variables of the Date data type can hold both a date and a time. The smallest value is midnight (00:00:00) of Jan 1 of the year 1. The largest value is 11:59:59 PM of Dec. 31 of the year 9999.

• Date literals: A date literal may contain the date, the time, or both, and must be enclosed in # symbols:– #1/29/2013#, #1/31/2013 2:10:00 PM#– #6:30 PM#, #18:30:00#

Date Examples• Date Literal Example:

– Dim startDate as dateTime– startDate = #1/29/2013#

• Use the System.Convert.ToDateTime function to convert a string to a date value:– startDate = System.Convert.ToDateTime(“1/30/2003”)– If date string is entered in a text box:

• startDate = System.Convert.ToDateTime(txtDate.text)• Or startDate=Cdate(txtDate.text)

• Date data type format methods:– .ToLongDateString, etc.

Some Date Functions

• Now(): Current date and time• Today(): Current date• TimeOfDay• DateDiff:• Demo

– Days between two dates– Days to Christmas

• DateDiff(DateInterval.Day, Today(), #7/4/2013#)– Date data type properties and methods

Using Online Help

• MSDN VB Developer Center– http://msdn.microsoft.com/en-us/vstudio/hh388573.aspx– Learn/Visual Basic language

The If … Then Statement• If condition Then

Statements• End If• If condition Then

StatementsElse

Statements• End If• Condition:

– Simple condition:• Comparison of two expressions formed with relational operators:>, <,

=, < >, >=, <=• Boolean variable

– Complex condition:• Formed with logical operators: ( ), Not, And, Or

Example

• State University calculates students tuition based on the following rules:– State residents:

• Total units taken <=12, tuition = 1200• Total units taken > 12, tuition = 1200 + 200 per

additional unit.– Non residents:

• Total units taken <= 9, tuition = 3000• Total units taken > 9, tuition = 3000 + 500 per

additional unit.

Decision Tree

Resident or Not

Units <= 12 or Not

Units <= 9 or Not

ELSEIF Statement

• IF condition THEN statements [ELSEIF condition-n THEN [elseifstatements] [ELSE [elsestatements]]] End If

Select Case Structure

• SELECT CASE testexpression[CASE expressionlist-n

[Statements][CASE ELSE

[elsestatements]END SELECT

Select Case Example• SELECT CASE temperature

CASE <40TextBox1.text=“cold”

CASE < 60TextBox1.text=“cool”

CASE 60 to 80TextBox1.text=“warm”

CASE ELSETextBox1.text=“Hot”

End Select

The Expression list can contain multiple expressions, separated by commas.Select Case number

Case 1, 3, 5, 7, 9textBox1.text=“Odd number”

Case 2, 4, 6, 8, 10textBox1.text=“Even number”

Case ElseEnd Select

Loop

• FOR index = start TO end [STEP step][statements][EXIT FOR]NEXT indexDO [{WHILE| UNTIL} condition][statements][EXIT DO]LOOP

Find the Sum of All Even Numbers between 1 and N

Dim sumEven, myN, i As Integer myN = CInt(TextBox1.Text) sumEven = 0 For i = 1 To myN If i Mod 2 = 0 Then sumEven += i End If Next MessageBox.Show("The sum of even numbers is: " + sumEven.ToString)

Do While

sumEven = 0i = 1Do While i <= myN If i Mod 2 = 0 Then sumEven += i End If i += 1LoopMessageBox.Show("The sum of even numbers is: " + sumEven.ToString)

With … End With

With TextBox1

.Height = 250

.Width = 600

.Text = “Hello”

End With

Convenient shorthand to execute a series of statements on a single object. Within the block, the reference to the object is implicit and need not be written.

Function

Private Function tax(salary) As Doubletax = salary * 0.1

End Function– Or

Private Function tax(salary) As DoubleReturn salary * 0.1

End Function

Procedures. Sub procedure:

Sub SubName(Arguments)…

End Sub– To call a sub procedure SUB1

CALL SUB1(Argument1, Argument2, …) •OrSUB1(Argument1, Argument2, …)

Call by Reference Call by Value

• ByRef– The address of the item is passed. Any changes

made to the passing variable are made to the variable itself.

• ByVal– Default– Only the variable’s value is passed.

ByRef Example

Private Sub Form3_Load(sender As Object, e As EventArgs) Handles MyBase.Load Dim myX, myY As Integer myX = 10 test(myX, myY) MessageBox.Show(myY) End Sub Private Sub test(x As Integer, ByRef y As Integer) y = 2 * x End Sub

ByRef, ByVal examplePrivate Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim myStr As String

myStr = TextBox1.Text

Call ChangeTextRef (myStr)

TextBox1.Text = myStr

End Sub

Private Sub ChangeTextRef(ByRef strInput As String)

strInput = "New Text"

End Sub

Variable Scope• Block-level scope: declared within a block of code

terminated by an end, loop or next statement.– If city = “Rome” then

• Dim message as string = “the city is in Italy”• MessageBox.Show(message)

– End if• Procedural-level scope: declared in a procedure• Class-level, module-level scope: declared in a

class or module but outside any procedure with either Dim or Private keyword.

• Project-level scope: a module variable declared with the Public keyword.