Vb Solved Qusetion Bank

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Q: Discuss the salient features of visual basic environment.

Ans:

Defining IDE

IDE is an acronym for Integrated Development Environment. The IDE is the workbenchon which you make your programs in Visual Basic.

The Visual Basic IDE is a collection of menus, toolbars, and windows that make up yourprogramming workbench. Each part of the IDE has features that affect different aspects

of your programming activity. The menu bar lets you direct the overall activity and

management of your programming. The toolbar enables you to access much of the menubar's functionality through various toolbar buttons. Forms--the basic building blocks of

Visual Basic programs--are presented in a Form window. You use the ToolBox to add

controls to the forms of your project. The Project Explorer displays the projects on which

you're working, as well as the different parts of each of those projects. You browse andset a control, form, and module's properties within the Properties window. Finally, you

position and view a form or forms onscreen within the Form Layout window.

Toolbars in the Visual Basic IDE

Toolbars are collections of small iconic buttons that reside in a bar underneath the menubar. These buttons offer access to the most commonly used functions that you have in the

Visual Basic menu structure. Toolbars are useful because rather than nevigating menus

and submenus to do what you want, you click a specific button in the toolbar to call aspecific functionality in the Visual Basic IDE.

ToolTips

ToolTips are little windows that appear when you hold the mouse pointer over a control

or toolbar button for a few seconds. Inside these windows is some text that tells you what

the control or toolbar button is about.

Using the Debug Toolbar

You use the Debug toolbar to test your program and resolve errors that might occur.

Using the Edit Toolbar

You use the Edit toolbar when you're working with code in a Code window. The features

of the Edit toolbar are similar to those of the Edit menu. You can Cut and Paste text.You can manipulate the layout of your code and do text selection, searches, and

replacement. Also, you can use automatic coding features such as Quick Info.


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An interesting VB IDE feature that the Edit toolbar uses is the Complete Word feature

(also trademarked by Microsoft as Intelli-sense). This feature automatically completes a

keyword for you. For example, if you were to type Ms into a code window and theninvoke the Complete Word feature, Visual Basic would complete the word as MsgBox,

an intrinsic Visual Basic function that displays a Windows message box. The Complete

Word feature is very useful for avoiding syntax errors due to misspelling.

Using the Form Editor Toolbar

You use the Form Editor toolbar to size, move, and align controls on a form. The Form

Editor toolbar has the same set of features as the Format menu.

You align and size multiple controls on a form with the Form Editor toolbar.

Using the Standard Toolbar

The standard toolbar is the central toolbar in the Visual Basic IDE. The standard toolbaroffers many features found in the File, Project, Debug, and Run menus.

The standard toolbar gives you fast access to often-used functionality and information.

ToolBox

Controls are the building blocks with which you assemble your Visual Basic program.

The ToolBox is a palette of controls, and you build your user interface by selectingcontrols from the ToolBox and placing them on your forms.

Some controls are built into Visual Basic and can't be removed from the ToolBox; thesecontrols reside within Visual Basic itself. These controls are known as intrinsic controls.

Others live outside Visual Basic and reside in files that end with the extension .ocx.These controls can be added and removed from the ToolBox.

This ToolBox shows both intrinsic controls and the extra ActiveX controls that ship with

Visual Basic 6.

Navigating Through the Form Window and Code Window

Just as controls are the building blocks that you use to assemble your Visual Basic

program, a Visual Basic form is the foundation on which you build with those blocks.Forms reside in the Form Designer window. You work in the Form Designer window to

add controls to your form.

The Form Designer window is where you create forms for your Visual Basic programs.

For each Form Designer window, you can also open a Code window. Code windows are

where you work with the Visual Basic code that you write "behind" your form. You open


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a code window by double-clicking a form or a control on the form. You also can open a

code window by choosing Code from the View menu.

Project Explorer

The Project Explorer in Visual Basic 6 helps you manage and navigate multiple projects.Visual Basic enables you to organize multiple projects into groups called project groups.

You can save the collection of projects in your Visual Basic session into a project group

file. Project Group files end with the extension .vbg.

The Project Explorer is a hierarchical tree-branch structure. Projects are at the top of thetree, and the project parts (forms, modules, and so on) descend from the tree. If you want

to work on a particular part, you double-click the part to display it. If you want to see the

part in a particular view--say, a form in a Code window--you select the form by clickingit once. Then click the View Code icon at the top of the Project Explorer window .

You can work with multiple projects in the Project Explorer window.

Add a form from the Project Explorer

1. Position the pointer on the white area of the Project window (not over a form

or any other item on the tree view).

2. Right-click to display the Project Explorer context menu.

3. Choose Add and then Form.

You can add or remove projects, forms, and modules to or from the Project

Explorer by using its context menu.

Properties Window

Properties and values

The programming jargonor terminology for a property's setting is a property's value.

In the Properties window, you read, configure, and control the initial settings of the

ActiveX controls in your program. As you become more familiar with Visual Basicprogramming, a good portion of your time will be spent learning, setting, and

manipulating control properties. Because controls are the building blocks of Visual Basicprograms, the Properties window is an essential tool to master.

You set the attributes of a control with the Properties window.

Setting Form Position with the Form Layout Window


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The Form Layout window enables you to set the runtime position of one or more forms

onscreen.

You position a form by moving its representation on the "computer screen" in the FormLayout window with your mouse. As you move the pointer over the small form in the

Form Layout window, the pointer changes into a four-directional, arrow-headed cross. Toposition the screen, hold down your mouse button and drag the form to where you want it

to be on the computer screen.

The Form Layout window lets you position one or more forms as they appear onscreen.

Viewing the IDE

MDI versus SDI

MDI stands for multiple document interface; SDI stands for single document interface. A

multiple document graphical user interface is one that allows you to view multiplewindows within a larger window--various Word document windows within the Word

application window, for example. A single document interface is one where all windows

appear independently of one another without the unification of a single parent window.

You can view the Visual Basic IDE in two ways: with the multiple document interface(MDI) or the single document interface (SDI). MDI view shows all the distinct windows

of the Visual Basic IDE as member windows within one large IDE window

In the SDI view, distinct windows of the Visual Basic IDE exist independently of each

other. There's no master window to contain and provide a unified feel to the IDE.

Q2. (a) what do you mean by variables and constants? Give the rules to define and use

them.

Ans:

Variable:

A Variable is an area that stores value during programs execution. This area has a name

i.e. a variable name and a value that varies from time to time. For example while

processing the salary of employee in an organization there can be a variable Emp-Name

used to store the names of employees. The value of this variable will vary while

processing salary for each employee.

Public intSalary As Integer

Constants

Constants are nonvariable variables. They resemble variables in the manner they aredeclared and assigned values. Unlike variables, the values they hold remain unchanged


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during program execution. To create a constant , you use the Const statement with the

following syntax:

[Public / Private ] Const constname [As type] = expression

Const Demo as string=rockConst arr_counter as integer=30

Visual Basic provides many built-in constants that are useful with various statements. ToSee a list of the valid constants, display the object browser and select Constants in the

classes/Modules dropdown list box.

Variable Naming Convention

At the time declaring a variable, the following naming convention should be consideredfor naming a variable:

It must begin with letter

It cant contain an embedded period, spaces or other punctuation characters.

It cannot exceed 255 characters.

It must be unique within its scope.

Data Types

Some data types perform faster than others do. Strategies for using certain data types for

certain uses and avoiding general use of others are essential for making an application as

efficient as possible. A brief overview of the most commonly used Visual Basic DataTypes are discussed below.

Visual Basic recognizes the following six types of variables:

o Numeric

o String

o Boolean

o Date

o Object

o Variant

Numeric

Visual Basic supports the following types of numeric data types listed below: Integer

A variable defined to be of the Integer data type is a signed integer

that is two bytes in length. Thus the value can range from 32,768

to 32,767

Long Noteit.zip


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Variables of data type long are also signed integers, except that

they are 4 bytes long. This gives them a range of 2,147,483,648 to

2,147,483,648

Single

Visual Basic provides several floating-point data types. The first,

the single data type is 4 byte value with range of 3.4*10-38 to 1.4*10-45 and 1.4* 10-45 to +3.4*10+38

Double

Whenever larger floating points values are required, the double

data type can be used. It takes 8 bytes to represent this variable andit should be used when a great degree of precision is required.

Currency

The Currency data type is an 8 byte number with fixed decimalpoint. It supports 4 digits to the right of decimal point 15 to the

left. It has been defined for monetary calculations.

Byte

The Byte data type stores an integer in the range of 0 to 255 in asingle byte. This data type is often used to access binary files,image files, sound files etc. This data type can also be used in

numeric calculations but the result should not be stored in another

Byte data type variable if it exceeds 255.

String

The string is a data type used to store alphanumeric data. It takes

one byte per character in the memory. The length of a stringvariable depends on whether the string declared is of fixed length

or variable length. A variable length string can store nearly 4

billion characters and the size of the variable varies as needed to

accommodate the values assigned to them.

The following assignments are all valid for a variable length string.

Dim Sampletxt As String

Sampletxt=DAV Institute Of management

Sampletxt=DAV

Sampletxt=

A fixed length can be declared as follows:

Dim As String * Where

is the name given to the variable

is the maximum number of characters that the variable can hold.


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For example refer the code :

Dim txt1 As string * 35



Private Sub cmdClick_Click()

txt1 = DAVIMText1.txt = txt1

txt2 = DAV Institute of MGMT.

Text2.txt = txt2

txt3 = DAV Institute of management

Text3.txt = txt3

End Sub

Boolean

The Boolean data types stores True/False values. Visual Basic allocates two bytes to

this data type.Boolean variables are internally stored as integer that take the value

1(for True) and 0 (for False)

Boolean variables are declared as :Dim No as Boolean

Date

Date and Time values stored internally in a special format. It is a double-prcesion

number,integer part represents the date and the fractional part represents time. A

variable declared as date can store both dat and time values.e.g. Dim Trans_date As Date

Trans_date = 02/02/1998

Trans_Date = 09/23/98 15:03:05 am

Object Variables

An object variable refers to one of Visual Basics many objects , and it can be used to

access the actual objects. For example, a Form has two command buttons on it,Command 1 and Command2. These can be declared as two object variables:

Dim x As CommandBotton , y As CommandButton


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Each of these two objects variables x and y , these can be manipulated just like

objects.For example refer the code below:

Private Sub Form_Load()

Dim x As CommandBotton, Dim y As CommandBottonSet x = Command1

Set y = Command2

x.Caption = OKy.Caption = Cancel

End Sub

VariantVisual Basic uses variant data type as the basis for the variables you create. The

variant is used most often to store numbers and strings, but it can store a variety ofother types of data.

Declaring Variables

Explicit Declarations

To declare the variable as Explicit Dim statement is used followed by the name of the

variable to describe what type of information will be stored within the variable, for

example:

Dim kms As Integer

Dim message As String

Implicit Declarations

In this type of variable declaration , whenever Visual Basic comes across an

undeclared variable type it creates new variant , the generic data type which canaccommodate all other data types.

For Example:

X = WelcomeThe sample code x contains the string value Welcome. Visual Basic automatically

creates x and selects a default data type for the variable.

Q3. (b) Write the steps to set a scroll-bar that facilitates a user to input a number in

the range 1-100

Ans:


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Properties of Scrollbar to Set

Min : 1

Max: 100

Value: 1

Private Sub HScroll1_Change()Text1.Text = HScroll1.Value

End Sub

Q4. Illustrate the use of with and exit for statements of Visual Basic.

Ans:

To Exit directly from for loop the Exit statement is used.

Example: Exit For


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Private Sub Command1_Click()

Dim t,I,p As Integer

I=InputBox(Enter the number for table generation:)

For t=1 to 10

If t=5 thenExit For

End if

P=i*tPrint I & * & t & = & p

Next t

End sub

The above example generates a multiplication table

With Statement

With statemnt is used to execute statements using a particular object. The syntax looks

like this:

With object

[statements]

End With

Private Sub Form_Load()With Label1

.Caption = "Say Hello, in ..."

.Font.Size = 10End With

With Combo1.List(0) = "French"

.List(1) = "German"

.List(2) = "Hawaiian"

.List(3) = "Hebrew"

.List(4) = "Italian"

.List(5) = "Japanese"

.List(6) = "Spanish"

.Text = "Language"

.Font.Size = 10

End With


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With Text1

.Text = ""

.BackColor = &H8000000A 'Gray

.BorderStyle = 0

.FontSize = 14

End With

With Command1

.Caption = "Quit"

.Font.Size = 10

End With

End Sub

Private Sub Combo1_Click()

Select Case Combo1.ListIndex

Case 0Text1.Text = "Bonjour"

Case 1Text1.Text = "Guten Tag"

Case 2

Text1.Text = "Aloha"

Case 3

Text1.Text = "Shalom"

Case 4

Text1.Text = "Buon Giorno"

Case 5

Text1.Text = "Konichihua"

Case 6

Text1.Text = "Buenos Dias"

End SelectEnd Sub

Private Sub Command1_Click()End

End Sub


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Q4. Write a program that finds the second largest element in the array, without

sorting

Q5. How will you build classes in Visual Basic ? discuss with an example.

Ans:

Object

An object is a self-contained piece of functionality that can be easily used, and re-used asthe building blocks for a software application.

Objects consist of data variables and functions (called methods) that can be accessed and

called on the object to perform tasks. These are collectively referred to as members.

Class

Much as a blueprint or architect's drawing defines what an item or a building will looklike once it has been constructed, a class defines what an object will look like when it is

created. It defines, for example, what the methods will do and what the membervariables

will be.

Defining a Visual Basic Class

Before an object can be instantiated we first need to define the class 'blueprint' for the

object. In this chapter we will create a Bank Account class to demonstrate the concepts ofVisual Basic object oriented programming.

Begin by starting Visual Studio and creating a new Windows Application namedvbObjects. Once the project opens, select theProject... menu and selectAdd class.... In

theAdd New Item dialog, name the new class file clsBankAccount.vb and click on the

Addbutton.


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Visual Studio will now add a new tab to code area for the new class file containing the

following class declaration:

Public Class clsBankAccount

End Class

We have now defined a class. The next step is to add some functionality to the class.

Creating Visual Basic Class Properties

Class members or properties are essentially variables embedded into the class. Memberscan bePublic orPrivate.

Public members can be accessed from outside the object. Private members can only be

accessed by methods contained in the class. This is the key to what is called data

encapsulation. Object-oriented programming convention dictates that data should beencapsulated in the class and accessed and set only through the methods of the class

(typically calledgetters andsetters).

We can now extend our BankAccount class to add member variables to hold the account

name and number. True to the concept of data encapsulation we will be creating methodsto access these values later, so will mark them asPrivate:


Private strAccountNumber As String

Private strAccountName As String

Private intBalance As IntegerPrivate accountFee As Integer = 5

End Class

Now that we have defined the properties of our class, the next task is to define methods

that will give us access to our data.

Defining Class Methods

Since we have declared our class data properties to be private, we need to

provide methods which will give us access to those properties from our code. This isachieved using Get and Set methods. The syntax for get and Set methods is as follows:

Public PropertypropertyName()Asdatatype Get .... Code to return property value

End Get


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Set(ByValvalueAsdatatype) .... Code to return property value

End Get

To demonstrate this we will add to our class to provide methods to get and set the

account number and name. Note that after you type in thePublic Property line of thedeclaration, Visual Studio automatically creates a template for the Get and Set methods,

which should be filled in as follows:


Private strAccountNumber As String

Private strAccountName As StringPrivate intBalance As Integer

Private accountFee As Integer = 5

Public Property AccountName() As String

Get

End GetSet(ByVal value As String)

End SetEnd Property

Public Property Balance() As Integer

GetReturn intBalance

End GetSet(ByVal value As Integer)intBalance = value

End Set

End PropertyEnd Class

Now that we have defined our getter and setter methods we can add our own method to

perform a task. This is the same as writing a Visual Basic function. The purpose of our

method will be to subtract the account fee from the current balance:

Public Function subtractFee() As IntegerintBalance = intBalance - intAccountFee

Return intBalance

End Function

When called, the above function subtracts the account fee from the balance, assigns the

new balance to the intBalance variable and returns the new total.


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Now that we have added some functionality to our class it is time to instantiate objects

from this class blueprint.

Instantiating an Object from a Visual Basic Class

The process of creating an object from the class 'blueprint' is called instantiation.Essentially, you instantiate an instance of the class and give that instance a name by

which you will refer to it when accessing members and calling methods. You can create

as many object instances of a class as you desire. Objects are instantiated from a classusing the new keyword. Visual Basic provides two ways to instantiate an object from a

class. These two alternatives are known as late-binding and early binding.

Late binding occurs when the assignment of the object to the variable occurs at run-time

when execution reaches the code where the object is created. There are drawbacks to thisapproach in that any syntax checking is not performed until the application runs because

the compiler has no way of checking whether you are referencing valid class members,

resulting in potential run-time exceptions. Another disadvantage is that execution can beslowed when using late-binding since much of the work performed by the compiler when

using early binding has to be performed at runtime.

Late binding is achieved using the new keyword as follows:

Dim objBankAccount As Object

objBankAccount = New clsBankAccount()

Early binding, on the other hand, has none of the draw backs of late-binding. The

compiler performs syntax checks to ensure the object is being used correctly andexecution speed is increased because the binding takes place at compile time - not at run-time.

Early binding is performed as follows:

Dim objBankAccount As clsBankAccount

objBankAccount = New clsBankAccount

It is also possible to instantiate the object at the same time that it is declared:

Dim objBankAccount As New clsBankAccount()

Accessing Object Properties and Methods

Now that we know how to write a class and instantiate objects from the class, we now

need to know how to call the methods we created in the class. First, you will recall thatwe created Get and Set functions the data members of our class. Because we did this, we


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can change and access these properties simply by referencing them as we would any

other property. For example:

Dim objBankAccount As New clsBankAccount()

objBankAccount.AccountName = "John Smith"

objBankAccount.Balance = 1230

MessageBox.Show(objBankAccount.AccountName & " has a balance of " &

CStr(objBankAccount.Balance))

The above code excerpt assigns values to the AccountName and account balance

properties of our object. It then references the properties in order to display a string which

reads "John Smith has balance of 1230" in a MessageBox.

We can also call our subtractFee() method as follows:

Dim objBankAccount As New clsBankAccount()Dim intNewbalance As Integer

objBankAccount.AccountName = "John Smith"objBankAccount.Balance = 1230

intNewbalance = objBankAccount.subtractFee()

MessageBox.Show(objBankAccount.AccountName & " has a balance of " &

CStr(objBankAccount.Balance))

The result will be a message which reads "John Smith has balance of 1225", since theaccount fee has now been subtracted from the balance.

Q6. What is debugging ? How does Visual Basic help in it?Ans:

DEBUGGING

No matter how carefully a programmer designs and codes application, the programs aresure to have a few errors. These errors are generally detected when the program is tested.

Debugging basically means finding and removing errors from the programs. These errors

in the program can be in their syntax or logic. Visual Basic not only assists us in tracingwhat is happening in the application while it is running, it also helps in diagnosing the

program errors as we write through its automatic syntax check and various other tools

which helps in remembering the keywords and syntax as we type the code.


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To detect and correct logical errors VB provides tools that allows us to pause a running

application inspects its condition step through individual statements and procedure make

changes to variable and code and resume execution.

Break Mode

In Visual Basic you are primarily working in two modes: Design Mode and Run Mode.

Design Mode:

In this mode the code is created and edited and the effects cannot be checked until the

code is executed(run).

Run Mode: The Programs execution can be checked , but no changes can be made tothe code.

Break Mode: It halts the operation of an application and gives a snapshot of its condition

at any instant as the program is still active. Only its execution is temporarily suspended.All variables retain their values , properties and statements. In this mode , you can modify

an applications code or observe the applications interface condition, or determine theactive procedures that have been called or even change the program flow.

If visual basic encounters any of the below mentioned statements then it enters into breakmode:

1) Breakpoint

2) Stop Statement

Break Mode can be entered manually in several ways:

1) You press CTRL+BREAK

2) Select the Break button on the toolbar

3) Press F5 while your program is running

Setting Breakpoints

A breakpoint works as marker in the code that tells Visual Basic to suspend programexecution. By setting the breakpoint at a place makes it easy to investigate which line has

suspended the program execution. Breakpoints are temporary and are not preserved with

the code i.e. when you close the project after setting the breakpoints and then reopen theproject , then the breakpoints will be gone.

To set a breakpoint

1. Select new project from the file menu

2. Select standard EXE as project type

3. double click on the form

4. Select the forms paint event as shown in figure


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5. Position the insertion point anywhere in the line of a procedure where the

program execution is to be halted.Lets say that you want to place it at a line

given below the code.

Print The loop is incremented for & y & times

Private Sub form_paint()

Dim x As String

Dim y As IntegerFor y = 1 To 5

x = InputBox("Enter your name below")

Print x

Print "The loop is incremented for " & y & "times"Next

Print

Print "loop is ended"

End Sub

Watch Statement

Watch Statement basically helps you to tell visual basic to observe a particular variable

and enter a break mode when a particular condition occurs.

The watch window helps in monitoring the behavior or expression as the programexecutes.

Adding a watch expression1. The following code already exists

Private Sub form_paint()Dim x As String

Dim y As Integer

For y = 1 To 5

x = InputBox("Enter your name below")Print x

Print "The loop is incremented for " & y & "times"

NextPrint

Print "loop is ended"

End Sub


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2.

The immediate window

The immediate window is used to query variables and object

Property values, and to run the code. You can use the immediate window to testprocedures, evaluate expressions , or assign new values to variables or properties in thecode. The immediate window displays information that results from debugging

statements you have placed in the code or that you typing commands directly in the

window.

To evaluate expressions , you print the immediate window.:

1. In Break mode, enter print methods directly in the immediate window.2. Include Debug print statements in the application code.

The scope or the immediate window is limited to the current procedure only. This

includes only local variables declared within the current procedure, module variables

declared within the current code module, and gloabal variables. Any variables orproperties out of scope are not displayed

Debug.Print statement


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The debug object s print method sends output to the immediate window without entering

Break mode.the following syntax is used , where the [items] is an expression or list of

expression to print if omitted, a blank line is printed.

Debug.print[items][;]

Locals Window

A Local window displays the current value of variables

Q7. How will you draw the following figure in Visual Basic?Ans:


Picture1.Circle (1000, 1000), 800, vbRed

Picture1.Line (172, 1000)-(1800, 1000), vbRedPicture1.Line (1000, 172)-(1000, 1800), vbRed

Picture1.Line (1800, 172)-(1800, 2000), vbRed

End Sub

Q8. Write short notes on any two of the following:

(i) Database support in VB(ii) Recursion

(iii) Creating MDI applications.

Q9.(a) Explain all Object based features of VB.

(b) what is control array ? How is it created?

Ans:

Control Array

A Control Array is a group of controls that share the same name and type. They alsoshare the same event procedure. Acontrol array has at least one element and can grow to

as many elements as your system supports. The maximum index you can use in the

control array is 32767. elements of the same control array have their own proipertysetting and control arrays are used in menu control and option but on groupings.


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The advantage of using control arrays is thet they need less resources than simply adding

multiple controls of the same type to form at design time. They are also useful if you

want several controls to share code.

At runtime , if you want to create control , then that control must be member of a control

array, each new element inherits the common event procedure of the array.

Creating a control array

There are three ways to create a control array at design time.

Assign the same name to more than one control.

Copy an existing control and then paste it onto the form.

Set index property to a value that is not null.

To add a control array to a form

1. Select the New Project from the File menu

2. Select standard.Exe project type.

3. Draw the TextrBox controls on the form as shown in figure:, the control will becomethe first element in the array.

4. Set the text boxs properties as follows:

Name Property to txtArrText Property clear Text1

Index property to no value


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5. Select Textbox and press Ctrl+C or select Copy from the edit menu.

6. Click on the Form. Press Ctrl+V or select paste from the Edit menu. And place a

copy of textbox on the form.7. A dialog box appears to confirm whether you want to create a control array. Click on

Yes to create a control array.

8. Drag the new text box to a position directly below the original .9. Select the original text box and observe that the index property has changed from no

value to a value of 0.

10. Paste another copy of text box control on the form as shown in figure below.

Writing code for Control Arrays:

Private Sub txtarr_GotFocus(Index As Integer)

txtarr(0).Text = "Jyoti"

txtarr(1).Text = "B-12,Sec-20,Noida"

txtarr(2).Text = "U.P"

End Sub

Q10(a) How is an array declared in VB ? Explain the static and dynamic arrays in VB

Ans:

An array is a group of related data items that share a common name. These arrays may

contain the days of the week, months of the year, a list of valid employee numbers, or anyother group of related information. Let us consider the following situation:


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We are provided with marks of 30 students. We wish to compute the average marks and

find out the number of students who have secured more than average marks. To find outthe number of students who have secured more marks than the average marks, we need to

compare all of the 30 marks with the average. We must therefore store marks in 30

different memory variable names such as mark1, mark2mark30. A neat and simplesolution to the problem is to define a single variable marks to store all the 30 marks. This

variable should refer to 30 values.

To declare an array in Visual Basic use the following statement

Dim x(5) as integer

In the above statement Dim is the keyword use for declaration

X(5) is the name of the array which can hold 5 values

All values are of integer type

In other words, Arrays are used to refer to a series of variables by the same name. They

use an index to refer to the individual elements. Some important points to be noted about

arrays are:All the elements in an array have the same data type.

We can declare an array of the fundamental data types i.e integer, float etc

Arrays are declared with DIM statement followed by the name of the array and the upper

bound in parenthesis. The upper bound cannot exceed the range of a LONG data type.

DIM PLAYER(10)

In the above example, PLAYER is the name of an array that can hold 11 elements. 11 isthe upper bound of the array and 0 is the lower bound of the array. By default, the lower

bound of an array is 0. Thus in the above example we have declared an array that

contains 11 elements (0-10).

Values can be assigned to the elements of an array as shown below:

Player(0) = RohitPlayer(1) = Anil

.

Player(10) = Rajiv

The keyword AS can be used optionally to specify the type of the arrays elements.


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We can explicitly set the lower bound of the array .

DIM PLAYERS(1 TO 10) AS STRING

CLASSIFICATION OF ARRAYS

STATIC ARRAYS or FIXED SIZE ARRAYS: Those arrays which are always of the

same size and their size cannot be changed at run time

DYNAMIC ARRAYS: Those arrays whose size can be changed at run time.

CONTROL ARRAYS: The arrays which holds controls of visual basic are called Control

Arrays

Example of Static Arrays


Dim marks(5) As Integer

For i = 0 To 5marks(i) = CInt(InputBox("Enter marks"))

Next i

End Sub

Q11. How are functions and subroutines declared in VB? Expalin with examples. Also

discuss different ways of passing of parameters.

What Are Subroutines

Subroutines can be thought of as miniature programs. A subroutine has a name

attributed with it, much like a variable does. Unlike a variable, a subroutine doesn't hold

data. Instead, it holds code. When the code in a subroutine is executed, the subroutine is

said to be "called". Therefore, one subroutine can "call" another subroutine. Somesubroutines are called automatically when certain actions are performed. For example,

the Form_Load subroutine is automatically called when a form loads. This is where you

have been inserting your test code before. What you were actually doing was adding codeto this subroutine.

Why Use Subroutine

You may ask yourself why subroutines would even be used. Why wouldn't you simply

put all of your code in one place? Subroutines are useful because they eliminateredundancy. Consider a complicated program like a word processor. When certain


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actions are performed, such as closing the program, opening a file, or closing an

individual file, the word processor would probably check to see if you had modified your

document. If the user had modified the document since they opened it, the user would beprompted to save the file before performing the action. You could imagine that checking

if the document was modified, prompting the user, and acting on the input would require

many lines of code. If the programmer had literally typed this code into all of the placesin the program where this check was to be made, it would still work fine. However, what

would happen if the way the program handles documents changed, and therefore this

code needed to be changed? The programmer would have to change the code in everyplace where this check was made. Even worse, what if the programmer changed the code

in a few places but not in another? This would lead to bugs that are difficult to track

down. Instead, if this code was put in a subroutine, the subroutine would simply be called

from all of these places. If the code then needed to be changed, the programmer wouldonly have to change it in one place; inside the subroutine. By doing this, subroutines

eliminate redundant code, making the entire program easier to manage.

Creating A Subroutine

Creating a subroutine involves two lines of code. Luckily though, the Visual Basic codeeditor is smart, and will insert the second line for you! A subroutine begins with the word

"Sub", followed by a space, then a name identifying the subroutine. Two parentheses

follow, which are used for a parameter list. Don't worry about these yet, they will becovered later in the lesson.

Sub TestSub()

EndSub

After you enter the first line and press Enter, the second line will automatically be addedfor you. These lines represent the start and end of the subroutine. Any code inserted

between these lines will be executed when the subroutine is called. A subroutine can be

called in one of two ways: using the Call keyword, or by simply stating its name.

Sub TestSub()MsgBox "Code in TestSub()"

End Sub


MsgBox "Code in Form_Load()"

TestSub

MsgBox "Back in Form_Load()"End Sub

You can also use the Call keyword, as mentioned above:

Sub TestSub()

MsgBox "Code in TestSub()"End Sub


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MsgBox "Code in Form_Load()"'This line is functionally equal as the line in the previous example

Call TestSub

MsgBox "Back in Form_Load()"End Sub

Subroutine Scope

The declaration of a subroutine has an optional keyword that can be used before "Sub".

You may enter a keyword representing scope here. "Private" and "Public" are examples

of scopes. You may have noticed that the Form_Load subroutine has the word "Private"before "Sub". This declares that this subroutine has a Private scope. If you don't specify

the scope of a subroutine, Visual Basic will use a default scope. You should never rely on

default scope, however. Get in the habit of always explicitly declaring the scope of your

subroutines.

What Is Scope

In the context of subroutines, scope represents where in your program the subroutine can

be called from. Subroutines with a Private scope can only be called from the source filefrom where they were defined. Subroutines with a Public scope can be called from

anywhere in your program. For example, a subroutine with a Private scope in a form can

not be called from another form, whereas it can if it has a Public scope.

Why Use Scope?

Why would you ever limit where you can call a subroutine from? Why wouldn't you

make all subroutines Public so that there are no limitations on your program? Subroutine

Scope is one of many tools that programmers can use to find bugs. If you know that yoursubroutine should never be called from a different source file, you should declare the

subroutine to be Private. This will prevent you from making a silly mistake and calling

this subroutine where it shouldn't be called. This will prevent mistakes that could be

extremely damaging and hard to detect. Instead, your program will crash with an errorrather than executing the subroutine with unpredictable results.

Parameters

Parameters, also called Arguments, are variables that can be "passed into" a subroutine. A

subroutine with parameters looks like this:

Private Sub DisplayAdd(x As Integer, y As Integer)MsgBox x + y

End Sub


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DisplayAdd 5, 2

End Sub

A new subroutine has been declared called DisplayAdd. This declaration is different than

the declarations that you have seen so far, however, as code has been added between theparenthesis. From your knowledge of variables, this syntax should look somewhat similar

to you. x As Integer and y As Integer appear to be variable declarations without

the "Dim" keyword. These declarations are separated by a comma. These variables are

the Parameters for the DisplayAdd subroutine. Code within the subroutine can access x

and y as usual, as if they were normal variables. However, when the subroutine is called,the calling subroutine will also provide values for these parameters. Therefore, the

subroutine has now become dynamic. The code can act on input without caring where the

input came from. When the Form_Load subroutine calls DisplayAdd with the parameters5 and 2, the code within DisplayAdd is executed. The first line adds x and y together and

displays the result. x and y have already been filled with the values 5 and 2 from the

Form_Load subroutine. The calling subroutine doesn't have to use numeric constants,however. It can use variables as well:

PrivateSub DisplayAdd(x AsInteger, y AsInteger)

MsgBox x + y

EndSub

PrivateSub Form_Load() Dim a AsInteger

Dim b AsInteger

a = 5

b = 2DisplayAdd a, b

EndSub

This code has identical results. Note that DisplayAdd cannot access a and b. As far as

DisplayAdd is concerned, a and b are represented as x and y. Attempting to access a or bfrom DisplayAdd would result in an error.

ByRef and ByVal

Parameters can be sent to a subroutine By Reference (ByRef) or By Value (ByVal).

ByRef is the default, and means that changes to the variable in the subroutine will resultin changes to the source variable outside of the subroutine. ByVal literally copies the

values of the variables from the calling subroutine into the called subroutine. By doingthis, the variables can be changed, but their values will not change outside of the calledsubroutine. ByVal can also be a lot slower with large variable types, however, since

memory has to be copied from one location to another. If you don't have any reason to do

so, there is no need to pass variables ByVal. You can explicitly state the way that a

variable is passed to a subroutine by using these keywords before the variable name.Using the ByRef keyword, one could write a Swap function, which switches the values of

2 variables.


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PrivateSub Swap(ByRef x AsInteger, ByRef y AsInteger)

Dim temp AsInteger

temp = xx = y

y = tempEndSub

Private Sub DisplayVals(ByRef a As Integer, ByVal b As Integer)

'Don't worry about understanding the next line yet, it will be explained laterMsgBox "a = " & CStr(a) & vbCrLf & "b = " & CStr(b)

End Sub

Private Sub Form_Load()Dim a As Integer

Dim b As Integer

a = 10b = 12

'Display values, swap, and display again

DisplayVals a, b'The next line is functionally identical to "Swap a, b"

Call Swap(a, b)

DisplayVals a, bEnd Sub

Notice that Call was used instead of simply stating the subroutine name. When using the

Call method however, you must use parenthesis when calling the subroutine. Note that

this program would also have worked without typing "ByRef" anywhere, since it is thedefault. The ByRef and ByVal keywords are rarely used in simple programs, however,

but it's a nice trick for your toolkit.

Functions

Subroutines have a close cousin called Functions. Functions are basically the exact same

as subroutines, except that they return a value. That means that the function itself has atype, and the function will return a value to the calling subroutine based on the code that

it contains. An example of this would be a function that adds two numbers, shown below.

A function is declared the exact same way as a subroutine, except using the "Function"keyword instead of "Sub". To return a value, assign a value of the proper type to the

function's name, as if it were a variable.

Private Function Add(ByVal x As Integer, ByVal y As Integer) As Integer

Dim Res as integerRes = x + yAdd = Res

EndFunction


Dim a As Intege


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Dim b As Integer

Dim c As Integer

a = 32b = 64

c = Add(a, b)

MsgBox ("Sum is : " & c)End Sub

Functions Or Subroutines

The best way to determine which is better for your application is by asking yourself a

simple question. Will you need to return a value? If so, use Functions. If you don't, use

subroutines.

Q12. Discuss important events , VB statements and methods with respect to form object.Also discuss the various parts of MDI form.Ans: Given in Question bank

Q13. discuss the following basic Active-X controls in VB with suitable examples:

(a) Scroll Bar control

(b) Image Control command button.Q14. Write Short notes on the following :

(a) OLE

(b) DLLAns: Given in Question bank

Q15. Write a program in VB that draws a diamond, an arrow , a box and an oval on the

form.

Q16. Discuss error handling statements and objects in VB briefly.

Ans: Given in Question bank

Q17. What are the different ways to organize data files in VB ? Explain different modesand I/O statements for handling data files.

Ans: Given in Question bank

Q18. what do you mean by data controls ? How are these used to access database ? writeall steps.

Ans: see also in question Bank

Database Management


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A database can be viewed as a set of interrelated data. Databasemanagement deals with the storage, retrieval and editing of the data withinthe database. One of the most important functions of Database managementis the Database security and Database validations.

Visual Basic makes it simple by supplying a variety of tools and approaches

for data management. For significant database applications, utilizingdatabase functionality that already exists becomes necessary. Visual Basic6.0 provides full-fledged database engine called Jet. This engine containsvirtually all the database functions that applications may need. The simplestand easiest way to access the Jet database engine is through bound datacontrol.

Data Access Object (DAO) has been the standard database access method forVisual Basic programmers. DAO was the first database interface includedwith Visual Basic in its third version.

Remote Data Object (RDO) was then introduced to make data-access moreflexible and functional in VB 4. The most recent release by Microsoft with

Visual Basic is the ActiveX data object, which is in a short while going to takeover all the other methods of data access.

Data Access Object

Data Access Object enables you to use a programming language to accessand manipulate data in local or remote databases and to manage databases,their objects and their structure. DAO utilizes Microsofts Jet database engineand can be used to access a wide variety of database formats, including,ISAM (Indexed Sequential Access Method) and Text.

In addition to this, DAO can also make use of Open Database Connectivity

(ODBC) databases through its ODBC Direct Object Model.Generally ODBC is a special technique to access a database residing on aseparate Server such as Informix, Oracle etc.

The DAO object model has 17 types of objects like Databases, RecordSets,Fields etc. Databases are accessed by opening an existing Database objector creating a new one. The individual fields in a table make up a RecordsetsField object and table of a database is held in a Recordset Object.

Data Access object is implemented through an ActiveX control called theData Control. This allows a large amount of DAOs power to be utilizedwithout having to add a single line of code. When used in conjunction with

Data aware controls such as TextBox, DBList, DbCombo, DbGrid etc, the Datacontrol becomes very powerful.

Information from a database table is fetched by the DAO and then supplied tovarious Data aware controls like TextBox, DBListBox etc.

Databases accessible through the DB Engine are FoxPro 2.0 to 3.0 and VFP,dBase III, IV and 5.0, Paradox 3x, 4x and 5x, Microsoft Access 1x to 3x, ODBCdatabases, Microsoft Excel 3.0 to 8.0, Lotus 1-2-3, WKS, WK1, WK3 and WK4,ASCII tabular Format, HTML Tabular Data and Microsoft Exchange 4.0 The


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DBEngine consists of several Dynamic Link Libraries that are linked to yourVisual Basic program at runtime. DBEngine is controlled by our applicationthrough DBEngines object classes, their methods and properties.

Data Binding

In order to display the values of the columns accessed by the Data Control,some controls are required which support the data control. These control arecalled Data Bound controls and are simpler to use e.g., TextBox, LabelDBGrid, DBList etc.

These controls have basically two standard properties other than their regularproperties. The DataSource property enables you to specify the name of theData Control to which the client control will bind. The name of the DataControl(s) available on your form is already present in the dropped downCombo Box of this property in the property window.

The Datafield property, a string property of the Client Control, specifies whichof the Database field names available from the data control the client willbind.

After the DataSource and Datafield properties are set, the Data Control isproperly initialized, the Client Control automatically displays the contents ofthe bound field as the data control is used to navigate though the recordset.

You can then use an appropriate editable control, such as the textox, tochange the Data contained in the Bound field. DBCombo and DBlist enableyou to use the data control to provide a list of valid choices for a field, as wellas to bind the client control to a specific field.

Data Control and The Data Bound Controls

Visual Basic provides many sources to connect to a data source. DataControl is one of them. Data Control was the first medium to connect theapplications to a database in the third version of Visual Basic.

The Data control is an excellent tool for rapidly developing a databaseinformation retrieval system. With very little code you can get a useful viewinto stored information. This is practically a drop-in-place process where byyou can place a data control, A DBGrid and a Command Button on a form andbe able to access your database in a matter of minutes. After you setproperties your application is set to go.

Data Control

Data Control is one of the easiest modes to access databases. You canperform most data access operations using the Data control without writingany code at all. Data-aware controls bound to a Data control automaticallydisplay data from one or more fields for the current record or, in some cases,for a set of records on either side of the current record. The Data controlperforms all operations on the current record.


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If the Data control is instructed to move to a different record, all boundcontrols automatically pass any changes to the Data control to be saved inthe database. The Data control then moves to the requested record andpasses back data from the current record to the bound controls when itsdisplayed.

The Data control is itself smart enough to handle a number of contingenciesincluding empty recordsets, adding new records, editing and updatingexisting records, and handling some types of errors. However, in moresophisticated applications, you need to trap some error conditions that theData control cant handle. For example, if the Microsoft Jet database enginehas a problem accessing the database file, doesnt have permission, or cantexecute the query as coded, a trappable error results. If the error occursbefore your application procedures start or due to some internal errors, theErrors event is triggered.

Data Control in Action

Using the data control

The data control is an intrinsic control used to bind that is, create aconnection- between a database and control such as text boxes. A databaseis sent to data control via its properties. Then individual control is bound todata control.

To add a data control to a form:

1. With a form open, double-click the data control in the toolbox (Figure9.1). The data control is placed on the form (Figure 9.2).

Figure 9.1


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Figure 9.2

2. Using the properties window, change the caption of the data control tosomething descriptive, such as click here to control data display (Figure9.3).

Figure 9.3

Figure shows navigation buttons that are build into the data control.

To connect the data control to a base

1. With the data control open in the properties windows, select the database name properties in the left column (figure 9.4)

Figure 9.4

2. Click the ellipsis in the right column. The data base name dialog open(figure9.5)


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Figure 9.5

3. From your file system, select the database.

4. Click open.

Figure 9.6

The data base file now appears in the right column of the properties windows(figure 9.6). The sample biblio.mdb database is shown in the figure.

Tips

Visual basic is often used with Microsoft access databases. Access

databases file have the .mdb suffix. Visual basic ships two sample access databases- biblio.mdb and

Nwind.mdb- for you to experiment with. You can find these databases inyour visual basic home directory.

Data control properties assignments can also be made in code. Biblioconsists of publisher, author, and book table. Nwind is an inventorydatabase of fictional food- trading company

End of File and Beginning of File Actions

The Data control can also manage what happens when you encounter aRecordset with no records. By changing the EOFAction property, you canprogram the Data control to enter Addnew mode automatically. Theseproperties have been discussed later.

Alignment

You can program the Data control to automatically snap to the top or bottomof its parent form by using the Align property. In either case, the Datacontrol is resized horizontally to fill the width of its parent form whenever the


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parent form is resized. This property allows a Data control to be placed to anMDI form without requiring an enclosing Picture control.

Data Binding

In order to display the values of the columns accessed by the Data control,some controls are required which support the data control. These controlsare called Data Bound controls and are simpler to use e.g., TextBox, Label,DBGrid, DBList etc.

These controls have basically two standard properties apart from theirregular properties. The DataSource property enables you to specify thename of the Data Control to which the client control will bind. The name ofthe Data Control(s) available on your form is already present in the dropdown Combo Box of this property in the property window.

The Datafield property, a string property of the Client Control, specifieswhich of the Database field names available from the data control, the clientwill bind.

After the DataSource and Datafield properties are set, the Data Control isproperly initialized, the Client Control automatically displays the contents ofthe bound fields as the data control is used to navigate though the recordset.

You can use an appropriate editable control, such as the TextBox, to changethe data contained in the bound field. DBCombo and DBList enables you touse the data control to provide a list of valid choices for a field, as well as tobind the client control to a specific field.

Properties of The Data Control

BOFAction and EOFAction Properties

As discussed earlier the BOFAction and EOFAction properties return or set avalue indicating what action the data control takes when the BOF or EOF isencountered by Data control.

Syntax:

DataControlName.Recordset.BOFAction = value

DataControlName.Recordset.EOFAction = value

Different settings for the properties are :

Constant Value Description

VbBOFActionMoveFirst 0 Moves the record pointer back to the firstvalid record.

VbBOFActionBOF 1 Causes a validation event on the firstrecord, repositions

to the first record.

Above given values are for the BOFAction property, values for EOFActionproperty are :


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VbEOFActionMoveLast 0 Moves the record pointer back to the lastrecord.

VbEOFActionEOF 1 Causes a validation event on the lastrecord, repositions to the last record.

VbEOFActionAddNew 2 After moving past the last record, triggersan AddNew event after Validation event.

Connect Property

The Connect property sets or returns a value that provides information aboutthe source of an open connection, an open database, a database used in apass through query, or a linked table. This property is read/write fordatabase objects, new connection objects linked tables and tabledef objects.

This property is read only for Querydef objects and basic tables.

Syntax :

Object.Connect = databasetype; parameters

Database type specifies the type of database. This parameter can beexcluded for Microsoft Jet Databases.

Database Property

This property returns a reference to a database connected through a datacontrol.

Syntax :

Object.Database

The Database object created by the Data control is based on the controlsDatabase Name, Exclusive Read Only and Connect properties. Databaseobjects have properties and methods you can use to manage your data. Youcan use any method of a Database object with the Database property of aData control such as close and execute. You can also examine the intervalstructure of database by using its TableDefs collection and in turn, the Fields,Indexes Collections of individual TableDef Objects.

DatabaseName Property

The DatabaseName Property reads or sets the name and location of thedatabase. Setting the value in the data controls Database Name Propertywhile your program is running, changes the database to which the control isconnected. You must use the Refresh method to reopen the control afterchanging databases for a data control.

Syntax :


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DataControlName.DatabaseName = PathName

The following example closes a database referred by DBName variable afterconfirming from the user.

Private Sub OpenDatabaseNew (DBName as String)

ans = Msgbox(Close + Data1.DatabaseName+Now,VBYesNo,Confirm)

If ans = VBYes Then Data1.DatabaseName = DBName

Data1.Refresh

End If

End Sub

Exclusive Property

The Exclusive property reads or sets whether a database is opened for single

user or multiuser access. The data control exclusively reads or writes thedatabase at both design time and runtime, if set to True.

Syntax :

Object.Exclusive = True False

ReadOnly Property

ReadOnly property returns or sets a value that determines whether thecontrols Database is opened for read-only access.

Syntax :

Object.ReadOnly [ =boolean]The object expression evaluates to a data object and a Boolean expressiondetermines read/write access.

The controls Database object is opened with read-only access when set toTrue. Changes to data arent allowed. The controls Database is opened withread/write access to when set False.

You can use the ReadOnly property with a Data control to specify whetherdata in the underlying Database can be changed. For example, you mightcreate an application that only displays data. Accessing a Database usingread-only results in faster access.

For a Data control, this property is used only the first time a database isopened by your application. If your application subsequently opens otherinstances of the database, the property is ignored. For a change in thisproperty to take effect, you must close all instances of the databases andthen use the Refresh method.

Recordset Property


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The Recordset property sets or returns a Recordset object defined by a Datacontrols properties or by an existing Recordset object.

You can use the Recordset property like any other Recordset object. Forexample, you can use any of the Recordset methods or properties to examinethe structure of the Recordset objects underlying schema.

You can also request the type of Recordset to be created by setting the Datacontrols Recordset Type property. If you dont request a specific type, adynaset-type Recordset is created. Using the RecordsetType property, youcan request to create either a Table -, Snapshot or dynaset typeRecordset.

The syntax for the Recordset property is as follows :

Set Object.RecordSet = value

Object refers to a valid Data control name and value is any object variablecontaining a reference to a RecordSet object.

RecordSource Property

The RecordSource Property specifies the source of the records accessiblethrough bound controls on your Form.

Syntax :

Object.RecordSource = [SQL Query Table Name ProcedureName]

The object expression evaluates to a Data control. Values can be the nameof any table in the database specified by the DatabaseName property of the

Data control or any table defined in the database objects TableDefscollection. Value can be also a string variable or a string containing aSQL.query. It can also be the name of any stored procedure in the Database.

If you set the RecordSource property to the name of an existing table in thedatabase, all of the fields in that table are visible to the bound controlsattached to the Data control. For table-type recordsets (RecordsetType =vbRSTypeTable), the order of the records retrieved is set by the Index objectthat you select using the Index property of the Recordset. For dynaset-typeand snapshot-type Recordset objects, you can order the records by using anSQL statement with an Order By clause in the RecordSource property of theData control. Otherwise, the data is returned in no particular order.

If you set the RecordSource property to the name of an existing QueryDef inthe database, all fields returned by the QueryDef are visible to the boundcontrols attached to the Data control. The order of the records retrieved isset by the QueryDef objects query. For example, the QueryDef may includean ORDER BY clause to change the order of the records returned by theRecordset created by the Data control or a WHERE clause to filter therecords.


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You must use the Refresh method on a Data control to reopen the database ifthe RecordSource, property settings have changed and rebuild the dynaset inthe controls Recordset property.

Example 1

Data1.RecordSource = Select * from Emp where EMPID >=1001

Data1.Refresh

The Refresh Method

The refresh method when applied to a data control, opens or reopens adatabase specified in the DatabaseName property of Data control.

Syntax :

Object.Refresh

This refresh method also resets the current record back to the first record or(row) in the table.

Important Events Of The Data Control

Error Event

This event occurs only as the result of a data access error that takes placewhen no Visual Basic code is being executed. The general form of this eventprocedure is

Private Sub object_Error([Index As Integer,] dataerr As Integer,

response As Integer)End Sub

Index identifies the control if its in a control array, contains the indexnumber of the Data control. Dataerr returns the error number and responseis a number corresponding to the response you want to take, as describedbelow :


DataErrContinue 0 Ignores the error and continues theexecution of the program.

VbDataErrDisplay 1 Displays the Error message. This is bydefault.

Run-time errors can occur when none of your code is running, as when :

A user clicks a Data control button.

The Data control automatically opens a database and loads a Recordsetobject after the Form_Load event.


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A custom control performs an operation such as the MoveNext method,and AddNew method or the Delete method.

If an error results from one of these actions, the Error event occurs.

If an event procedure has not been written for the Error event, Visual Basicitself displays the message associated with the error.

Reposition Event

Reposition event occurs after a record becomes the current record. When aData control is loaded, the first record in the Recordset object becomes thecurrent record. Whenever a user clicks any button on the Data control,moving from record to record, or if you use one of the Move methods, such asMoveNext, the Find methods, such as FindFirst, or any other property ormethod that changes the current record, the Reposition event occurs after,when each record becomes current. Delete, Unload, Update are few actionscausing this event. The general form of this event is :

Private Sub Object.Reposition([Index As Integer])

End Sub

Index specifies the index number of control if it is a part of control array. Incontrast, the Validate event occurs before moving to a different record.Youcan use this event to perform calculations based on data in the currentrecord.

Validate Event

The Validate event occurs before the reposition event (or a different record

becomes the current record). Validate event procedure has two argumentsIndex number as integer for the Data control, if it is a part of a Data controlarray, Save a Boolean expresssion specifying whether bound Data haschanged or not and Action an integer specifying operation that causes thisevent. Values for action are :


VbDataActionCancel 0 Cancels the operation when the sub exits.

VbDataActionMoveNext 3 Caused due to MoveNext method.

VbDataActionMoveLast 4 Caused due to MoveLast method.

VbDataActionAddNew 5 Caused due to AddNew method.

VbDataActionUpdate 6 Caused due to Update method.

VbDataActionDelete 7 Caused due to Delete method.

VbDataActionFind 8 Caused due to Find method.

VbDataActionUnload 11 Caused due to Form being unloaded.


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This event occurs even if no changes have been made to data in the boundcontrols and even if no bound controls exist. You can use this event tochange values and update data. You can also choose to save data to stopwhatever action is causing the event to occur and substitute a differentaction.

You can change the action argument to convert one action into another. Youcan change the various Move methods and the Addnew method, which canbe freely exchanged. Any action can be stopped by setting action to 0.

You can check the data in each bound control where DataChanged is True.You can then set DataChanged to False to avoid saving that data in thedatabase. If it is invalid or corrupted, you can't use any methods such asMoveNext on the underlying Recordset object during this event.

Using Objects

Visual Basic allows you to create objects to represent a database, Recordsets,Fields etc. This makes the job easier in programming a Database application.

You can then easilty manipulate the objects or change the DataSourceaccording to your requirement in run-time.

Data Access Object (DAO) has been the simple Database access methods forVisual Basic programmers. You can use the Database and RecordSet objects.

The RecordSet and Database objects, each has properties and methods oftheir own. You can either use a Database, RecordSet object created by a Datacontrol or create an instance of you own, to manipulate the data.

Database Object

A Database object represents a Database. A Database object contains

Recordsets, QueryDefs, and Procedures. A Database object is declared withina Workspace object, which is a part of Workspace collection.

A database object can be declared using the following code :

Dim MyDb As Database

Dim MyWrk As WorkSpace

Set MyWrk = WorkSpaces(0)

Set MyDB = MyWrk. OpenDatabase

("C:\ProgramFiles\MicrosoftOffice\Office\Samples\_ Northwind.MDB)

The OpenDatabase method of the Workspace object opens a database andreturns its reference to a valid Database type object variable.

Important Methods Of A Database Object Are

Close Closes an open Database Access Object.

Execute Runs an Action Query or executes an SQL statement.


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ExecuteSQL Executes an Action Query as an SQL statement on anODBC database.

OpenRecordset Creates a new Recordset object and applies it to theRecordset collection.

Refresh Refresh method closes or rebuilds the Recordset object.

Important Properties Of the Database Object

Connect Specifies the source of an open database. The default sourcefor ODBC and certain

ISAM drivers in Jet databases.

Count Returns the number of objects in a collection.

Name Returns or sets a user defined name for data access objects.

Recordset Object

A Recordset object represents the entire set of records from a base table orthe set of records resulted by an executed query. At any time, Recordsetobject refers only to a single record within the set as the current record.

A RecordSet object can be used to manipulate, and access the data. In orderto navigate records in the Database you can use various methods of theRecordSet object.

The number of records returned by the Recordset can be determined bymoving to the last record in the Recordset or by examining the Recordsetobjects RecordCount property. Before you move to the last record, the valuereturned by the property to display the number of records in a Data controls

Recordset :

Data1.Recordset.MoveLast

MsgBox Records & Data1.Recordset.RecordCount

If you create a Recordset object using either code for another Data Control,you can set the Recordset property of the Data control to this new Recordset.Any existing Recordset in the Data control, and the Database objectassociated with it are released when a new Recordset is assigned to theRecordset property.

The five types of RecordSet objects are :

Table type Recordset

Dynaset type Recordset

Snapshot type Recordset

Forward only type RecordSet

Dynamic type RecordSet


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All the above mentioned RecordSet objects represent a set of records. Let usdiscuss these different types of RecordSets.

Table Type RecordSet Object

The first type of RecordSet object is the Table-type RecordSet. A table typeobject can be created from a table in a Microsoft Access database, but notfrom an Open Database Connectivity (ODBC) or a linked table. When youcreate a table-type the Jet database engine opens the actual table and yoursubsequent data manipulations operate directly on base-table data. A table-type can be opened on only one table; it cannot be opened on a union queryor a select query with a join.

The best part of this type of object is that you can use index created for theunderlying table. This allows much faster sorting and searching than theother types.

DynaSet Type RecordSet Object

Dynaset-type Recordset object represents a result of a query that can haveupdatable records. A dynaset-type object can be created from either a localor a linked table, or with a row-returning query that joins tables. Its actuallya set of references to records in one or more tables. With a dynaset you canextract and update data from more than one table, including linked tablesfrom other databases. Heterogeneous updatable joints are a unique featureof dynaset-they enable you to use updatable queries against tables indifferent types of databases. You can use the Seek methods rather than Findmethods for a Dynaset-type Recordset object for better performance.

SnapShot Type Recordset Object

A Snapshot-type object is a static copy of a set of records as it exists at thetime the snapshot is created. A snapshot-type object can contain fields fromone or more tables in a database. You cant update a snapshot.

The main advantage of a snapshot is that it creates less processingoverheads than the other types, so it can run queries and return data faster,especially when working with ODBC data sources.

Forward Only

A Forward-only type object is identical to a SnapShot type object. A forward-only-type object, sometimes referred to as a forward-scrolling snapshot or aforward-only snapshot, provides a subset of the capabilities of a snapshot.With forward-only snapshots, you can move only in a forward directionthourgh the records. Objects of this type cannot be cloned and only support


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the Move and MoveNext methods. Like snapshots, you cant update aforward-only-type object.

Dynamic Type Recordset Object

Dynamic type RecordSet object is a result of query from one or more basetables. You can add, change or delete records from a row-returning query.Besides this, records other users add, delete or edit in the base table are alsopresent in the RecordSet.

Although you can work with any of the above RecordSet object, you mustalways choose the correct RecordSet type, that suits or satisfies your desires.For example, you would like to work with the sorted data or a data wheresearching operations like FindFirst, Seek could be performed in a short spanof time, then you will go for indexed table type Recordset. Similarly, in orderto scan all the records you must use a Forward only type Recordset for betterperformance.

You can use the type argument of the Recordset object to choose theRecordSet type.

Important Methods of the RecordSet Object

AddNew

The Ms Access engine maintains a copy buffer where it keeps the pendingdata that it will be writing to the database.

The addnew method clears the copy buffer and moves the current record tothe end. This is like adding a new row.

Syntax:

Datacontrolname.Recordset.AddNew

TheAddnew method does not actually add the information to the database.This is done by the UPDATE method.

Update

This method sends the contents of the copy buffer to the table or dynaset.Syntax :

Datacontrolname.Recordset.Update

Example 2

Data1.Recordset.Addnew


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Data1.Recordset.Fields(Author) = Homes

Data1.Recordset.Fields(Titles) = Iliad

Data1.Recordset.Update

This code adds a record to a table which has two fieldsAuthors and Title.

Update Controls

This method can be used to retain the original data in the bound controls andignore the changes made to the data by a user.

For e.g., this method can be used in the Cancel button to reset the contentsof bound controls to their original value.

Edit

This method copies the current record into the copy buffer for editing.

Example :

Data1.Recordset.Edit

Authorname = Data1.Recordset.Fields(Author)

Call Changefield(Authorname)

Data1.Recordset.Fields(Author) = Authorname

Data1.Recordset.Update

This code uses a user defined procedure called Changefield, which changes

the value of the field.

Delete

This method deletes the current record in the recordset.

Syntax :

Datacontrolname.Recordset.Delete

After delete you must move the record pointer away from the deleted recordby a move method.

Example 3

Data1.Recordset.Delete

Data1.Recordset.Moveprevious

Close


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To close an open database attached to a data control or to close the specificrecordset currently attached to the control, use the following :

Syntax :

ObjectName.Close

ObjectName can be an open database, recordset, dynaset, snapshot ora table object.

You must use the update method before you close the database to save allthe pending changes made to the database.

UpdateRecord Method

Saves the current values of bound controls. Doesnt support namedarguments.

Syntax :

Object.UpdateRecord

The Object represents a RecordSet object.

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