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 procedures FullName: 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 procedures Sum: 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 =

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 DescriptionNumberToString()Result “N” or “n”Number format12.3ToString(“n3”) “F” or “f”Fixed-point scientific format ToString("f2") “E” or “e”Exponential scientific format ToString("e3")1.235e+005 “C” or “c”Currency format ToString("C")($1,234,567.80) “P” or “p”Percentage format.234ToString("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 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 – –Learn/Visual Basic language

The If … Then Statement If condition Then Statements End If If condition Then Statements Else 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 = per additional unit. –Non residents: Total units taken <= 9, tuition = 3000 Total units taken > 9, tuition = 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 <40 TextBox1.text=“cold” CASE < 60 TextBox1.text=“cool” CASE 60 to 80 TextBox1.text=“warm” CASE ELSE TextBox1.text=“Hot” End Select

The Expression list can contain multiple expressions, separated by commas. Select Case number Case 1, 3, 5, 7, 9 textBox1.text=“Odd number” Case 2, 4, 6, 8, 10 textBox1.text=“Even number” Case Else End Select

Loop FOR index = start TO end [STEP step] [statements] [EXIT FOR] NEXT index DO [{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 = 0 i = 1 Do While i <= myN If i Mod 2 = 0 Then sumEven += i End If i += 1 Loop MessageBox.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 Double tax = salary * 0.1 End Function –Or Private Function tax(salary) As Double Return salary * 0.1 End Function

Procedures. Sub procedure: Sub SubName(Arguments) … End Sub –To call a sub procedure SUB1 CALL SUB1(Argument1, Argument2, …) Or SUB1(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 example Private 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.