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Question Bank for Visual Basic

1) What is Visual Basic ? What are the various Editions of Visual Basic

Available in market ?

Visual basic is a powerful application development tool developed by Microsoft. It is

used for creating customized windows based programs. Visual Basic is the fastest and

easiest way to create application for Microsoft Windows. Visual Basic provides acomplete set of tools to simplify rapid application development, whether we are an

experienced programmer or new to windows programming. Visual Basic consists of two

parts Visual and Basic. The Visual part refers to the method used to create thegraphical user interface (GUI). Rather than writing numerous lines to code to describe the

appearance and location of interface elements, We simply add objects which are prebuilt

into place on screen. This part makes visual basic a true RAD ( Rapid ApplicationDevelopment) tool. The BASIC part refers to the BASIC language since Visual Basic is a

descendent of BASIC (Beginners All Purpose Symbolic Instruction Code) which was

often the first language that programmers used to learn in order to become familiar from

the original BASIC language and now contains several hundred statements , functions

and keywords , may of which relate directly to the Windows GUI. Visual Basic is not justa language but is an Integrated Development Environment (IDE). An IDE is basically a

term commonly used in the programming world to describe the interface andenvironment where we can develop , run , test and debug our applications.

The Visual Basic is available in the following three editions :

1. Learning Edition : It allows programmers to easily create powerful applications

for the Windows and Windows NT operating systems . Basically it contains all

the tools like Visual Basic development environment , standard controls,samples , Setup Wizard and other tools that are required for creating a powerful

application.2. Professional Edition : It adds to the capabilities of the Learning Edition by

allowing us to create client/Server or Internet Enabled applications. The

Professional Edition of Visual Basic has all the features that are found in the

Learning Edition and includes advanced features such as tools to develop ActiveXand Internet controls.

3. Enterprise Edition : In incorporate environment benefit by using the advanced

features in the Enterprise Edition to create robust distributed applications in ateam setting. It includes all the features found in the professional Edition. It also

includes Microsoft Visual Source Safe for source code control and the

Automation and Component Manager.

2) Define the following terms

Design Time : The time an application is being developed in the Visual Basic

Environment

Run Time : The time an application is running . At run time the programmer

interacts with application as a user would

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Controls : Graphical representation of objects such as command button, Textbox,

Label etc that are used by the user to provide information to the application

Properties : The features of an object such as size, caption or color

Methods : The actions that an object can perform or that can be performed on the

object

Forms : Customizable windows that serve as the interface for an application or asdialog boxes used to gather information from the user

Project : A Visual Basic application is comprised of one or more components that

are arranged under a project. The project is stored as a file with .vbp extension.

Objects : A general term used to describe all the forms and controls that make up

a program. In Visual Basic an application is a combination of Object like Form

and Controls. Procedures that respond to Events, and other general purposeprocedures. Objects in Visual Basic as basically considered as combination of

code and data which is treated and controlled as a unit. Command Buttons and

other controls on a form are objects. These objects form a major part of a Visual

Basic Application which allow the user to enter the data as well as view the

results. Each form in a Visual Basic project is a separate object. Events : Events are the actions recognized by a form or control. Events occur a

user, operating system or application interacts with the objects of a program. Any

action performed by pressing a key one the keyboard or clicking a mouse for

which code can be written is an event procedure that runs whenever the event

occurs as a result of the user actions or program code, or they can be triggered bythe system. Depending on the event the corresponding procedure is executed but

some events recognized by one object might not be the same as recognized by

other objects.

Event Driven Programming : When a program is event driven its code is executed

in response to events invoked by the user, operating system or application. This

differs from procedural programming where the program starts at the first line ofcode and follows a defined pathway calling procedures as needed. In traditional orprocedural applications the application itself determines which portion of code is

to be executed and in what sequence. Execution starts with the first line of code

and follows the coding sequence defined in the application. At times controls aretransferred to other parts of the program through statements and procedures.

Whereas application written in Visual Basic are event driven. In an event driven

application the code does not follow a predetermined path it executes differentcode sections in response to events. Events can be triggered itself by the user

actions, by messages from the system or other application or even from the

application itself. The sequence of these events determine the order in which the

code executes thus the path differs each time the program runs.

3) What are various types of projects available in Visual Basic Explain

The Various types of project available in Visual Basic are as follows

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Standard EXE A Standard EXE project is a typical and commonly used

project type.

ActiveX EXEActiveX DLL

These types of projects are available with the ProfessionalEdition. ActiveX components are basic code building

components. These are identical in functionality, but are

packed differentlyActiveX Controls This type of project is also a feature of professional edition.

ActiveX controls allow a user to develop their own custom

controls or use ActiveX controls such as textbox or commandbutton control which are basic element of the user interface

ActiveX Document Exe

ActiveX Document DLL

ActiveX documents are in essence Visual Basic applications

that can run in the environment of a container that supports

hyperlinks.VB Application Wizard

VB Wizard Manager

The Application Wizard provides a series of steps for setting

up the skeleton of a new application and the wizard manager

let the user builds its own wizard

A wizard is a sequence of windows that collect informationfrom the user. After the user fills out all the windows, the

wizard proceeds to build an application , install software orcarry out an automated operation for the end user.

Data Project This is a feature of Enterprise Edition. And it does not

correspond to a new project type. It is identical to the standard

Exe project type but it automatically adds the control that areused in accessing databases to the toolbox. It also adds the

database ActiveX Designers to the project Explorer Window.

The ActiveX Designers are visual tools for accessing andmanipulating databases and generating reports.

DHTML Application It allow us to build Dynamic HTML pages that can be

displayed in the browsers window on the client computerIIS Application It allow us to build application that run on the Web Server and

interact with clients over the internet with the internet

information Server.Addin It allows us to create our own add-in for the visual basic IDE.

Add ins are special commands that we can add to visual

basics menu

VB Enterprise EditionControl

This is not a new type of project but it simply creates a newstandard Exe project and loads all the tools of the Enterprise

Edition of Visual Basic

4) What is Visual Basic ? Explain its various features

Visual basic is a powerful application development tool developed by Microsoft. It isused for creating customized windows based programs. Visual Basic is the fastest and

easiest way to create application for Microsoft Windows. Visual Basic provides a

complete set of tools to simplify rapid application development, whether we are anexperienced programmer or new to windows programming. Visual Basic consists of two

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parts Visual and Basic. The Visual part refers to the method used to create the

graphical user interface (GUI). Rather than writing numerous lines to code to describe the

appearance and location of interface elements, We simply add objects which are prebuiltinto place on screen. This part makes visual basic a true RAD ( Rapid Application

Development) tool. The BASIC part refers to the BASIC language since Visual Basic is a

descendent of BASIC (Beginners All Purpose Symbolic Instruction Code) which wasoften the first language that programmers used to learn in order to become familiar from


and keywords , may of which relate directly to the Windows GUI. Visual Basic is not justa language but is an Integrated Development Environment (IDE). An IDE is basically a

term commonly used in the programming world to describe the interface and

environment where we can develop , run , test and debug our applications.

Features of Visual Basic are as follows

1. Global Object : To simplify the creation of reusable code libraries. Visual Basic

let us mark objects in a code component as global so that their methods can beinvoked without explicitly creating an instance of the global objects.

2. Portable : Both 16 bit application for windows 3.1 or 32 bit applications forwindows 95 and windows NT can be written using visual basic

3. OLE programmability : On can write OLE server application using visual basic

that can be manipulated from within other applications

4. Support to Client / Server architecture : It supports client server architecturewhich can share everything from data processing power , distributing the

responsible the responsibility for process and data integrity to the software and

hardware of both the client and server.5. Multiple Project : Open multiple projects in the same instance of Visual Basic.

Useful for debugging ActiveX controls.

6. Polymorphism : The implements features allows our classes to support multipleinterfaces. Users of our component can early bind these interfaces, regardless of

the object that implements them.

7. Code Editor Environment : Through this feature we can block and Unblockcomments adds and removes the comment character for each line of selected

block of text, list properties/methods presents a drop down list of properties

available for that control.

8. Wizards : The ActiveX Control Interface Wizards, ActiveX Document MigrationWizard , Data Form Wizard and Property Page Wizard are new . The Setup

Wizard has been enhanced to support distribution via the Internet.

5) What is an Integrated Development Environment ? Explain in detail

Visual basic is a powerful application development tool developed by Microsoft. It isused for creating customized windows based programs. Visual Basic is the fastest and

easiest way to create application for Microsoft Windows. Visual Basic provides a

complete set of tools to simplify rapid application development, whether we are anexperienced programmer or new to windows programming. Visual Basic consists of two

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parts Visual and Basic. The Visual part refers to the method used to create the

graphical user interface (GUI). Rather than writing numerous lines to code to describe the

appearance and location of interface elements, We simply add objects which are prebuiltinto place on screen. This part makes visual basic a true RAD ( Rapid Application

Development) tool. The BASIC part refers to the BASIC language since Visual Basic is a

descendent of BASIC (Beginners All Purpose Symbolic Instruction Code) which wasoften the first language that programmers used to learn in order to become familiar from


and keywords , may of which relate directly to the Windows GUI. Visual Basic is not

just a language but is an Integrated Development Environment (IDE). An IDE is

basically a term commonly used in the programming world to describe the interface

and environment where we can develop , run , test and debug our applications.

The various features of this environment are as follows

Visual Basic Menus : VB contains two types of menus :

o

Built In Menus : It appears on the menu bar across the top of VB window.Each menu contains commands that relate to the menu name. For example

Format Menu contains commands used for formatting our form. Some of

the commands have sub menus that contain more specific commands

o Shortcut Menus : These are those menus containing frequently used

commands that appear when we click the right mouse button or press

SHIFT+F10 . The specific list of shortcuts available from context menus

depends on the object on which we click the right mouse button.

Toolbar : The buttons in the Toolbar represents the controls we can include in

any program we develop. The toolbar is typically the main focus of our attention

as we begin a new project and choose controls to depicts the options, proceduresand activities we are planning in our application

Toolbox : The toolbox contains the objects and controls that can be added toforms to create the user interface of simple as well as complex applications. Even

additional controls can be added to the toolbox by using the Components

command on the Project menu.

Form Window: In the middle of the screen between all the toolboxes and other

windows, the form designer is place which is actually a workplace where we

actually design the layout of the application

Project Explorer Window : The project explorer window is quite similar towindow explorer which allows us to expand and collapse the subfolders.Projectexplorer is a quick reference to various elements forms, classes and modules in

our project.

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Property Window :It displays the various characteristics of the selected object .Each and every control for example a command button that appears on a form isalso an object and all characteristics of an object are called its properties.

Code Editor Window :In visual basic , the editor is called the Code Window.Code Window can be opened by double clicking on a form or control in the formlayout window.The code can be either associated with a form in our project or

contained in a separate code module. It contains two drop down list at the top of

the window; the object list contains a list of all the controls contained in the formand the procedure list displays all the event for that control

6) What are modules ? Explain its various types

Code in visual basic is stored in three kinds of modules viz. Class module, Form module

and Standard module. Single Application can consist of just a single form and all of code

in the application resides in that form module. At times as our application gets larger and

more complex we can add more forms. Eventually we may find that there is a certaincommon code we may want to execute in several forms and at the same time we does not

want to duplicate the code in the forms. So at that point we can create a separate modulecontaining a procedure that implements the common code . This separate module should

be a standard module. Each Standard, Class and Form module can contain :

Procedure : A sub , function or property procedure contains pieces of code thatcan be executed as a unit

Declarations : We can place constants , variables , procedure declarations at the

module level of form , class or standard module.

Standard Module: Standard modules (.BAS filename extension) are containers forprocedures and declarations commonly used by other parts of the application. They cancontain global or module level declarations of constants, variables, external proceduresand global procedures.

Form Modules: Form modules (.FRM filename extensions) are the foundations ofany visual basic application. They contain the textual description of a Form and its

control including their property settings. They can contain Form level declarations of

types, constants, variables and external procedures that handle events and generalprocedures. Form are a part of our application that are visible to users at run time.

Class Modules: Class modules (.CLS filename extension) mark up the foundation for the

object-oriented programming in Visual Basic. We can write code in Class modules tocreate new objects. These new classes can include their own customized properties,

methods and events. All of the properties and methods we create can also be used by

other object in our application.

7) What are the various step one has to follow for managing project

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Three main steps are used to create an application in Visual Basic are as under :

1. Creating an Interface

2. Setting Properties3. Coding

Creating an InterfaceForms are the foundation for creating the interface of an application. Forms can be used

to add windows and dialog boxes to the application. These can also be used as containers

for items that are not part of the applications interface. For example any application canhave a from that serves as a container for graphics that is planned to display in other

forms.

Creating a Form

The first step in building Visual Basic application is to create the forms that will be the

basis of the applications interface. To start with a new project use New project command

from File menu or click open button after selecting a project type from the first dialog

box titled as New project whenever you start visual basic for the first time.

Coding

Once we add objects on the form we have to set the objects properties. We can either set

the properties using the Properties windows at design time or use code to modify the

properties at run time. While setting the initial properties for the form and each objects

we can add code that executes in response to events. For example, Click is one event thatoccurs for command button being clicked.

8) What is Coordinate System ?The coordinate system is a two dimensional grid that defines location on the screen in a

form, or other container. We define locations on this grid using coordinates in the form :(x,y)The value x is the location of the point along the x-axis with the default location 0 tothe extreme left. The value y is the location along the y-axis with the default location of 0

at the extreme top.The upper left corner of the screen is always (0,0). The default

coordinate system for any container starts with the (0,0) coordinate in the upper-leftcorner of the container.

The following rules apply to the Visual Basic Coordinate System

When inside a picture box use the coordinate system of that control

Statements we move or resize a control we use the coordinate system of the

controls container. If we draw the object directly on the form, the form is thecontainer. If we draw the control inside a frame or picture box , the frame or the

control is the container.

All graphics and print methods use the coordinate system of the container. Forexample statements that draw that resize or move form always express the forms

position and size in twips. When we create code to resize or move a form, we

should first check the Height and Width properties of the Screen object to makesure the form would fit on the screen.

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Twips

All visual basic movement sizing and graphical drawing statements use a unit of one

twip. A twip is 1/20 of a printers point.

9) What is Form and explain the various properties of the form and also

list the various events which are associated with a form

A Visual Basic form is used to develop the user interface . It is basically a window where

we can different elements in order to create a complete application. Every application wesee on the screen is based on some type of form. Forms have their own properties , events

and methods which are used to control their appearance and behavior. A default form

Form1 is add to development environment when Visual Basic starts. It applies a defaultset of properties to this form and any forms that are added to the project. The properties

of these forms can be changed for its appearance and behavior at design time or at run

time.

Properties of form

1. Border Style property: It determines how the border of a form behaves and looks.This property is used for setting form size that can be set at design time and

cannot be changed at run time.

Setting Description

0-None None (No border)

1-Fixed Single This setting that the forms cannot be resized by dragging

2-Sizeable It is default setting for Visual Basic forms and most otherwindow applications. The form can be resized by dragging

borders

3-Fixed Dialog It can include control menu box and title bar4-FixedToolwindow

It displays a nonsizeable window with a close button

5-SizeableToolWindow

It displays a sizeable window with a close button, but does notinclude a maximize or minimize button .

2. Caption Property : It is a text that appears on the title bar of the form. The captioncan be set either at design time by using Caption property in the properties

window or by writing code at run time

3. ControlBox : The control menu is a simple menu that allows the user to restore ,move , resize , minimize , maximize and close a form. This button can be enabled

in the form by setting the forms controlbox property in the forms propertywindow. It can set to true or false. When we set to true then also set the Borderstyle property to either 1,2 or 3 to display the control box.

4. Font : It is used to set the font for use in the form. Whatever controls are placed

on the form will be by default use the font set for the form. Double click-click

font property.5. Name : In Visual Basic the name property is the most important property as it is

the name of the control that is refers to when the program runs. The default name

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for a new form is Form plus a unique integer. The form name property is

prefixed by letters frm and can include numbers with an underscore.

6. Window State : This property is responsible for how the form starts up. By settingany of the three options the display of the form can be determined.

Options Effect

0-Normal Opens form in the normal state1-Minimized Opens form in the minimized state

2-Maximized Opens form in the maximized state

Form Events

1. Load : It occurs when the form is loaded in to memory

2. Activate : It occurs when the form is displayed initially or when the user returns

from one form to another form3. Deactivate : It occurs when the user moves to another form or form is hidden

4. Unload : It occurs when the form is unloaded from memory

5. Initialize : It occurs when an instance of the form object is created6. Terminate : It occurs when an instance of the form object is destroyed

10) What are controls and Explain its various types in details

Controls are objects that are placed within form objects. Command buttons, List boxes

and Scrollbars are examples of controls. Each type of control has its own set of

properties, methods and events suitable for a particular purpose. The controls can beadded to a form by just double clicking on the control or by drawing the selected control

on a form by dragging the mouse around the area where we want the control to be placed.

When a control is created, Visual Basic gives a default name indicating the type of

control, plus a unique integer which can be changed by starting it with a letter followedby number.

Classification of controls

There are two types of controls in Visual Basic

1. Standard controls: The Standard Controls also known as Intrinsic Controls are

always available on the toolbox

2. ActiveX controls: These are those controls which can be added later on to thetoolbox. This can be either third party controls like some of them are provided by

Microsoft or can be user created controls.

Standard controls

Label

A Label control is a graphical control we can use to display text that user cant changedirectly. It used to display static information. It displays read only text; the user cannot

edit the text directly. The property which is set in a label control is the caption property

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which can be set either at design time or run time. At design time we set the property by

selecting it from the controls properties window. At run time we can set the caption

property to provide instruction or additional help to the user.

Commonly used Label Properties

Name : It returns the name used in code to identify the label.

Caption: It determines the text displayed in the label

Alignment : Specifies how the caption will be aligned in the label. The values 0,1

and 2 indicate left,right and center alignment

AutoSize : It returns or sets a value that determines whether whether label is

automatically resized to display its entire contents

BackStyle : It returns or sets a value indicating whether a label control istransparent or opaque

BorderStyle : It returns or sets the border style for an object . It determines

whether a visible border appears around the label or not

Wordwrap : It returns or sets a value indicating whether a label control with its

Autsize property set to True expands vertically or horizontally to fit the textspecified in its caption property.

Textbox

To obtain fill-in-the-blank information from the user or to display information providedby the application . It can be used in conjunction with a Data Control to display

information from a database. It is also used to set up database queries or to edit records in

a database.

Commonly used TextBox properties

Name : It returns the name used in code to identify the Textbox. Borderline : The default borderstyle is 1 which provides a thin line around the

box.

Enabled : It returns or sets the value that determine whether or not the textbox can

respond to user generated events.

Maxlength : It returns or sets a value indicating whether there is a maximum

number of characters that can be entered in the Textbox control and if so specifiesthe maximum number of characters that can be entered.

MousePointer : It is used to change the mouse pointer shape. The default shape is

I-beam

Multiline : It returns or sets a value indicating whether a Textbox control canaccept and display multiple lines of text.

PasswordChar : It is used for displaying specified character when a password is

typed by the user.

ScrollBars : It sets a value indicating whether the textbox has horizontal or

vertical scroll bars.

Text : It returns or sets the text contained in the edit area of textbox.

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Frame Control

A Frame control provides an identifiable group of controls. It acts as container for othercontrols typically option button or checkboxes.

Commonly used Frame properties

Caption : It determines the caption to the frame control

Enabled : It determines whether a control can respond to user generated events.

Name : It gives a name to identify the frame

Visible : It returns or sets a value indicating whether the frame is visible or

hidden.

Command Button

It used to begin , interrupt or end a process. When chosen a command button appears

pushed in and so is sometimes called push button. One can attached an access key to acommand button by placing an ampersand (&) before a character in the caption property.

Commonly used Command button properties

Caption : It returns or sets the text is displayed in the command button

Name : It returns the name used in code to identify the command button

Value : It returns or sets a value indicating whether the button is chosen. This is

not available at design time

CheckBox

It used to give the user a True/False or Yes/No option . One can use checkbox control in

groups to display multiple choices from which the user can select one or more.

Commonly used checkbox properties are

Alignment : It specifies the alignment of the checkbox with respect to the caption

Caption : It specifies the text appears besides the checkbox

Enabled : It sets a value that specifies whether the checkbox can respond to user

generated events

Name : It assigns a name to identify the checkbox Value : It is used to specify the state of checkbox. The value 0 or false indicates

that the checkbox is deselected . Value 1 or true indicates that the checkbox is

selected.

Option Button

An option button control displays an option that can be turned on or offCommonly used checkbox properties are :

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Alignment : It specifies the alignment of the option button with respect to the

caption

Caption : It specifies the text appears besides the option button

Name : It assigns a name to identify the option button.

Value : It returns the state of the option button

ScrollBar

A ScrollBar enables the user to select a value by positioning it at the desired location. Itrepresents the set of values. The Min and Max property represents the minimum or

maximum value. The value property of the ScrollBar represents its current value, which

is any integer between the minimum and maximum value. The Horizontal and Verticalscrollbar are identical as they share the same properties , events and methods.

File System Controls

These controls are used to add the file handling capabilities to the application. They arenormally

DriveListBox : It normally used in conjunction with DirListConroll and filelist

control .It used to select a drive.

DirListBox : It is used to display file and folders of the selected drive

FileListBox : It is used to select a file or files of select directory.

Timer

The timer control is one of the few controls always hidden at run time. It can execute

code at regular interval . It has some important propertiesInterval : The interval property is measured in milliseconds and is represented bya value from 1 to 65,535

Enabled : The enabled property determines if the timer control will invoked the

timer event in the time specified by the interval property.

OLE ( Object Linking and Embedding)

Reuse is a central goal in software design . Reusing instead of rewriting code saves

development effort. ActiveX controls are reusable software components that can quickly

add specialized functionality to web sites, desktop applications and development tools.

ActiveX controls are a component object model (COM) technology. It is softwarearchitecture that allows application to be built from binary software components . COM

is the underlying architecture that forms the foundation for higher level software services,

such as those provided by OLE a technology for transferring and sharing informationamong applications, It is based on dynamic data exchange. It gave developers the ability

to add new interfaces to an OLE component without needing to recompile the

components clients.

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Common ActiveX controls

Status Bar

It is a control that is displayed at the bottom of application window and displaysinformation about the current state of the application. The status bar control can display

and update certain types of information automatically. Set the style property to display

the following :1. Keyboard status for the CAPS LOCK, NUM LOCK,INSERT, and SCROLL

LOCK keys

2. Time

3. DateIt can contain text and bitmaps. We can display messages from the application in the

status bar using the Text property

TreeView Control

It is used to display information within a tree hierarchy. It is made up of nodes that arerelated to each other in some way. It display a hierarchical list of nodes objects, each of

which consist of a label and an optional bitmap. After creating a treeview we can add ,

remove , arrange and otherwise manipulate Nodes objects by setting properties.

ListView Control

It displays data as ListItem objects. Each ListItem object can have an optional iconassociated with the Label of the object. The ListView property is often used in

association with a tree view control. The ListView also has several properties which canviewed using the property window.The property page in addition to the general tab hasthe following

1. ImageList Tab to associate to a particular ImageList

2. Sorting Tab to display fields that expose the properties related to storing in aListView control

3. Column Header tab using which the index field is incremented every time a

Columnheader object is added to the List View control

ListView control can be used

To display the results of a query of database

To display all the records in a table

In association with a TreeView control to give users an expanded view of

TreeView control node.

Progress Bar

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This control allow us to graphically represent the progress of a transaction. The control

consists of a frame that is filled as the transaction occurs. The value property determines

how much of the control has been filled. The Min and Max properties set the limits of thecontrol

Slider Control

It consists of a scale , defined by the Min and Max properties and a thumb which the user

can manipulate using the mouse or arrow keys. At run time the Min and Max propertiescan be dynamically reset to reflect a new range of values. The Value property returns the

current position of the thumb. Using the events such as the MouseDown and MouseUp

events , the slider control can be used to graphically select a range of values. Its working

is same like the progress bar except that the looks of the two controls are different.

11) What are Data types ? Explain the various data types available in

Visual Basic ?

Data types are explanation of data stored in the variables.Visual Basic also supportsmost of the fundamental data types used in several programming languages.

Data Type Storage size

Byte 1 bytes

Boolean 2 bytes

Integer 2 bytes

Long 4 bytes

Single(floating point) 4 bytes

Double(floating point) 8 bytes

Currency 8 bytes

Decimal 14bytesDate 8 bytes

Object 4 bytes

String (variable length) 10 bytes + string length

String (Fixed length) Length of string

Variant 16 bytes

User Defined Number required by elements

Byte Data type

Byte variables are stored as single , unsigned 8-bit numbers ranging in value 0-255. The

byte data type is useful for containing binary data

Boolean Data type

Boolean variables are stored as 16-bit numbers but they can only be true or false.

Example :

Dim x as Boolean

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x=true

Numeric Data type

The following data types are used for storing numeric values depending on data storage

requirements

Whole numbers Integer or longFraction-Single, Double or Currency

Example :

Dim age as integer

Dim ID as long

Dim sum as singleDim price as currency

Date Data TypeData variable are stored as 64-bit floating point numbers. They represents dates ranging

from 1 january 100 to 31 December 9999 and times 0:00:00 to 23:59:59.

Dim mydate as Date

String Data Type

To store any text in a variable one can declare the variable as string data type. There are

two kinds of strings variable length and fixed length strings.

A variable length strings can contain upto 2 billion charactersA fixed length strings can contain 64K characters.

Dim name as string

Variant Data Type

The variant data type is the data type for all variables that are not explicitly declared assome other type. The variant data type has no type declaration characters.

Dim avar

Object Data Type

Object variables are stored an 32 bit addresses that refers to objects. Using the set

statement a variable declared as an Object can have any object reference assigned to it. Avariable declared as Object can be assigned to any object recognized by the application.

12) What are variables ? Explain the variable naming convention ?While performing calculations one may need to store values temporarily . One may also

need to store the values calculated by more than one method and then have to compare

the values. Variables are used to store values like numbers, strings and dates.A variable is

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a named temporary storage location. A variable is capable of containing a certain type of

data that can be modified during program execution.

Variable naming convention

Must begin with a letter

Cannot contain an embedded period

Cannot exceed 255 characters.

A variable has a variable name by which it is referred to and can store a value into it. For

example there is variable name Radius to store a value in it as

Dim Radius as floatRadius=4.5

A variable has to be created first only then one can use it

Empty variables

If a variable has been declared but not value is assigned to it , it is said to empty variables

Static Statements

Variables declared with the static statement retain their values as long as the code is

running

Public Statement

Used at module level to declare public variables and allocate storage space. Variable

declared using the Public statement are available to all procedures in all modules in allapplication

Private StatementUsed at module level to declare private variables and allocate storage space. Privatevariables are available only to the module in which they are declared.

Scope of Variable

The scope of variables refers to the accessibility or visibility with in the project. The level

at which the variable is declared determines the accessibility of a variable.

It is important for variables used with in procedures :

Procedure level variables are recognized only in the procedure in which they are

declared Local variables declared with static statement exist as long as the code is running

while the variable declared with Dim statement exist only as long as the

procedure in the module but is not available to code in other modules.

A module level variable is available to all procedures in the module but is not

available to code in other module

If public variables in different modules share the same name, it is possible todifferentiate between them in code. For example if integer variable Myint is

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declared in Form1 and Module1 one can refer to it as Module1.Myint and

Form1.Myint

Converting Variable Types

Visual Basic provides certain conversion functions one can used to convert values from

one datatype to another.Function Description

Asc Returns the character code corresponding to the first letter in a

string

Chr Returns the character associated with the specified character code

Cbool Converts an expression to a Boolean

Cbyte Converts an expression to a Byte

Ccur Converts an expression to a currency

Cdate Converts an expression to a date

Cdbl Converts an expression to double

Cint Converts an expression to int

CLng Converts an expression to longCSng Converts an expression to string

CStr Converts an expression to string

Cvar Converts an expression to variant

13) Write Short note on User Defined Data type

Any data type one define using the Type statement is called user defined datatype. User-defined data types can contain one or more elements of a datatype.

Declaring a userdefined datatpye

Type StudenttypeRollno as string

Name as string

Class as stringTmarks as integer

End type

Now declare variable of the user defined datatype

Dim student1 as studenttype

Storing values in user define datatype

Student1.rollno=A45

Student1.name=RahulStudent1.class=BBA(CAM)

Student1.tmarks=345

14) What is Constant ?

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A constant is meaningful name that takes the place of a number or string that does not

change. A constants value cannot be changed.

For exampleConst pi=3.14

What is an operator ? Explain the various types of operators available

in Visual Basic with the help of an example ?

Operators are special symbols or words used to describe an operation or an action which

is to take place between two or more or among more than two values.Operators are available in Visual Basic for performing arithmetic,comparison and logical

operations.

The different categories of operators in Visual Basic are

Arithmetic operator

Comparison operator

Logical operator Concatenation operator

Arithmetic operators

These operators are used to perform mathematical operations on two numbers or numericexpression. The list of the arithmetic operators are

+,-,*,/,Mod

Comparison Operator

The comparison operators are used to compare expression. They compare expressionsand return a Boolean value.

Operator Description

> Greater than

< Less than

>= Greater than equals to


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*:for matching more than one characters in string

Program of Like operator

Private Sub Command1_Click()Dim x As String

x = "hello"

Dim yy = x Like "m*"

MsgBox y

End Sub

IS Operator

It is used to compare two object reference variables and returns two if both the objectsnames refers to the same object.

Syntax result = object1 is object 2

Program of IS operator

Private Sub Command1_Click()Dim x As CommandButton

Dim y As CommandButton

Dim z

z = x Is yMsgBox z

End Sub

Logical operator

Logical operator are used to combine conditions and returns a Boolean value. Commonly

used logical operator are AND,OR and NOT

Private Sub Command1_Click()

Dim a, b, c As IntegerDim d

a = 10: b = 8: c = 6

d = a > b And b > c

MsgBox dd = a > b Or b > c

MsgBox d

d = Not (a > b)MsgBox d

End Sub

Concatenation operators

These are used to join to expression

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MsgBox "hello" & "Visual Basic"

End Sub

15) What is Loop Statements ? Explain the various types of Loop

statementsLoop structures of Visual Basic are used for iteratively performing a statement /

statement block. They are used when a group of statements have to be executed

repeatedly based on a condition.

FOR.LOOP

This is used when the repetition is to be done for a certain number of times and a countermay be used.


Dim i As Integer

For i = 1 To 10MsgBox "i=" & i

Next iEnd Sub

Another Example of FOR LOOP


Dim i As Integer

For i = 1 To 10 step 2

MsgBox "i=" & iNext i

End Sub

DO While Loop

This loop test the condition first and if true executes the statement which are given in the

loopPrivate Sub Command1_Click()

Dim i As Integer

i = 1Do While i


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While i 10

MsgBox "i= " & ii = i + 1

Loop

End Sub

16) What is an Array ? Explain with the help of an example ?

An array is a contigous area in memory referred to by a common name. All elements in

an array have the same data type. The size of the array is a specified at the time of

definition of the array. An array allows us to set variables by the same name and anumber to tell them apart. The memory occupied by the data can be calculated by

multiplying the number of data elements by the size of each elements.

Syntax : Dim x(5) as integer


Dim x(5) As IntegerFor i = 0 To 4x(i) = InputBox("Enter value")

Next i

For i = 0 To 4MsgBox (x(i))

Next i

End Sub

Dynamic Arrays

A dynamic arrays can be resized at any time. It is possible to change the size of array at

run time using ReDim statement. If you create a dynamic array. A dynamic array can becreated by giving an empty dimension list.

For example

Dim x() as integerRedim x(5)

Example of Dynamic Arrays


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Dim x() As Integer

Dim i As Integer

i = InputBox("Enter the size")ReDim x(i)

For a = 1 To i

x(a) = InputBox("enter the number")Next a

For a = 1 To i

MsgBox (x(a))Next a

End Sub

17) Difference between an Event and General Procedure

In Visual Basic event procedures are invoked in response to keyboard , mouse or system

action. Our code can also explicitly invoke event procedures. The maximum number of

events a control can have is fixed . Event procedures are stored in a form module and areprivate by default.

A general procedure is not executed unless explicitly invoked. One can create a general

procedure either by choosing the procedure from the insert menu or by typing the

procedure heading Sub followed by the procedure name on a blank line.

18) What is an Event ? Explain the Event Driven programming model ?

Explain the various types of events?

Events : Events are the actions recognized by a form or control. Events occur a user,

operating system or application interacts with the objects of a program. Any actionperformed by pressing a key one the keyboard or clicking a mouse for which code can bewritten is an event procedure that runs whenever the event occurs as a result of the user

actions or program code, or they can be triggered by the system. Depending on the event

the corresponding procedure is executed but some events recognized by one object mightnot be the same as recognized by other objects.

Event Driven Programming : When a program is event driven its code is executed inresponse to events invoked by the user, operating system or application. This differs from

procedural programming where the program starts at the first line of code and follows a

defined pathway calling procedures as needed. In traditional or procedural applications

the application itself determines which portion of code is to be executed and in whatsequence. Execution starts with the first line of code and follows the coding sequence

defined in the application. At times controls are transferred to other parts of the program

through statements and procedures. Whereas application written in Visual Basic are eventdriven. In an event driven application the code does not follow a predetermined path it

executes different code sections in response to events. Events can be triggered itself by

the user actions, by messages from the system or other application or even from the

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application itself. The sequence of these events determine the order in which the code

executes thus the path differs each time the program runs.

Event Driven Programming Model

1. The application starts and a from is loaded and displayed2. The form receives and event. The event would have been caused by the user

called as user initiated events. The event would have been caused by the system

itself is called system initiated events3. If there is code in the corresponding event procedure it executed

4. The application waits for the next event

Types of events

In Visual Basic program basically two types of events can occur :

1. User Initiated Events: These are those that occur in response of an action takenby the user. It includes keystrokes and mouse clicks but other events are also

carried out by the user, either directly or indirectly. For example when the userclicks on aTextbox to start editing the information on the Textbox the click event

is fired to the textbox. Along with it several other events are also fired such as

GotFocus which occurs every time the user moves to the textbox either by

clicking the mouse or using the Tab key. Similarly when the textbox gets the programs focus another control must lose the focus. This action causes a

LostFocus event to fire another control. The GotFocus and LostFocus events are

caused by the users action just as the Click event.2. System Initiated Events: Even though we design and code the programs with

utmost care, run time errors can always occur in our program. A run time error

occur when the user tries to open a file when the file does not exists or when hetries to read a from the disk without inserting a disk in the floppy drive. These

error generates an event and these handled by operating system. The events which

are caused by the system itself are known as System initiated events.

19) What is an object ? Why do we require them ? Explain in detail ?

When we create an application in Visual Basic we work with objects. We can use objects

provided by Visual Basic Such as controls, forms and data access objects. We can also

control other applications objects within our visual basic application. We can even createour own objects and define additional properties and methods for them.

An object is a combination of code and data that can be treated as a unit. An object canbe a piece of an application like a control or a form. An entire application can also be an

object. Software objects are often used to model real world objects we find in everyday

life. As the name implies Objects are key concept in understanding object orientedtechnology. We can look around ourself and see many examples of real world objects :

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dog , lion etc. These real world objects share two characteristics : they all have a state and

they all have a behavior. For example dog have state (name, color, breed) and behavior

(barking and fetching) . Software objects are modeled after real world objects in that theytoo have state and behavior. A software object maintains its state in variables and

implements its behavior with methods. The following table describes examples of the

types of objects we can use in Visual Basic :

Example Description

Command Button Controls on a form such as command button and frames are

object

Form Each form in a Visual Basic project is a separate object

DataBase Database objects are objects and contain other objects likefields and indexes

Chart A Chart in Microsoft Excel is an object.

Each object in Visual Basic is defined by a class. For example The controls on the Toolbox in Visual Basic represents classes. The objects

known as control doesnt exist until we draw it on a form. When we create acontrol we are creating a copy or instance of the control class. That instance of the

class is the object we refer to in our application.

The form we work with at design time is a class. At run time Visual Basic createsan instance of the forms class.

An object provides code we dont have to write. For example we could create our

own File Open and File Save dialog boxes. Instead we can use the common dialogcontrol provided by Visual Basic. We could write our own scheduling and

resource management code. We can use the Calender , Resources and Task

objects provided by Microsoft Project. Visual Basic provides the tools to allow us to combine objects from different

sources. We can now build custom solutions combining the most powerful

features of Visual Basic and applications that support Automation. Automations is

a feature of the Component Object Model (COM) an industry standard used byapplications to expose objects to development tools and other applications.

20) What is a Class ? Explain the Various features of OOPS

A class is a blueprint or prototype that defines the variables and the methods common to

all objects of a certain kind. In the real world we often have many objects of the same

kind. For examples our car is really just one of the many cars in the real world. Usingobject oriented terminology we say that our car object is an instance of the class of

objects known as cars. All cars have some state and behavior. However each cars state is

independent of and can be different from other cars. While producing cars ,manufacturers take advantage of the fact that cars share characteristics and they build

many cars from the same blueprint it would be inefficient to produce a new blueprint for

every individual car manufactured.

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Features of OOPS

1. Abstraction : It is the process of selecting essential features of an entity thatdescribe it completely. Humans manage complexity through abstraction. For

example people do not think of a car as a set of thousands of individual parts.

They think of it as a well defined objects with its own unique behavior. Thisabstraction allows people to drive the car without being overwhelmed by the

complexity of the parts that form the car. The can ignore the details of how the

engine , transmission and braking system works. Instead they are free to utilizethe object as a whole.

2. Encapsulation : This refers to the fact that objects hide the details of how they

internally work. For example when we set the Text property of a toolbox, we as a

user do not know how the textbox internally repaints the characters. This can alsobe termed as information hiding.

3. Inheritance It is the idea that a class can gain the pre-existing interface and

behavior of an existing class. This is done by inheriting these behaviors from the

existing class through a process known as sub classing. The class from whichanother class is derived is the super class and the class that inherits the code from

the super class is known as sub class.4. Polymorphism : It is the ability to write one procedure that can operate on objects

from more than one class treating different objects from different classes in

exactly the same way. For example an operation may exhibit different behavior in

different instances. The behavior depends upon the types of data used in theoperation. For example consider the operation of addition. For two numbers the

operation will generate a sum . If the operands were strings then the operation will

be concatenation.

21) What is an API ? Explain them in detail

An API is simply a set of functions available to an application programming. This term is

most often used to describe a set of function that are a part of one application but are

being accessed by another application. When a Visual Basic program uses OLEautomation to execute an Excel spreadsheet function we can say that is accessing the

Excel API. API is one of those acronyms that seems to be used primarily to scare people.

The DOS interrupt function can technically be considered the DOS APT. The Windows

API refers to the set functions that are a part of windows and are accessible to anyWindows application. When we consider that the windows API has literally thousands of

functions. From the point of view of Visual Basic programmer , the windows API

functions can divided into four categories1. API functions that correspond to VB feature : Many API functions are already

built into VB so that there is no need to access them via the Declare statement.

2. API function that cannot be used from VB : There are number of API functionsthat simply cannot be accessed from VB. In most cases this is because they

require parameters that incompatible with VB

3. API functions that are useful for VB programmers

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4. API functions that cannot be directly called from VB but can be accessed through

a simple interface that performs certain parameters conversions or allows access

to information that cannot be obtained directly

22) What are Dynamic Link Libraries (DLL) ? What are the benefits ofusing DLL?

When we need capabilities that do beyond the core language and controls provided withVB we could make direct calls to procedures contained in DLLs. By calling procedures

in DLLs we can access the thousands of procedures that form the backbone of Microsoft

Windows operating system as well as routines written in other languages.

As their name suggests, DLLs are libraries of procedures that applications can link to and

use at run time rather that link to statically at compile time. This means that the libraries

can be updated independently of the application and many applications can share a single

DLL. Microsoft windows itself is comprised of DLLs, and other applications call theprocedures within these libraries to display windows and graphics, manage memory or

perform other tasks. These procedures are sometimes also referred to as the WindowsAPIs or application programming interfaces.

Benefits of DLLs

1. Accomplish tasks not available in VB DLLs can perform tasks that are not

possible in VB directly. For example we can invoke a DLL procedure that causes

our application to remain the topmost window.2. Improve performance -- DLLs execute much faster than VB code. If we have a

procedure that requires maximum performance, we can write a DLL procedureand then invoke the DLL from VB

3. Get Update independently of the application DLLs can be updated without

recompiling the application that invoked the DLL. This provides greater

modularity and application maintenance.

23) What are Dialog Boxes ? Explain it ?

Dialog boxes are used to display information for the user or to prompt the user for typing

appropriate data. The easiest way to add a dialog box to application is to use a predefined

dialog because we dont have worry about designing , loading or showing the dialog box.

However our control over its appearance is limited. Predefined dialog boxes are alwaysmodal which they must be closed before we can continue working with the rest of

applications. MsgBox and InputBox are the functions used for creating such dialog

boxes.

24) Differentiate between MsgBox and InputBox ?

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Message Box displays a message in a dialog box waits for the user to click a button and

returns an integer indicating which button the user clicked. We can use the MsgBox

function to get Yes or No responses from users and to brief messages such as errors,warnings or alerts in a dialog box. After reading the message the user chooses a button to

close the dialog box.

Syntax :

Msbox (prompt,[button][,title])

Prompt Required : Sting Expression displayed as the message in the dialog box. The

maximum length is approximately 1024 characters depending on the width of the

characters used.Button (optional) : Numeric expression that is the sum of values specifying the number

and type of buttons to display , the icon style to use , the identify of the default button and

the modality of the message box. If omitted the default value for buttons is 0.

Title (optional) : String expression displayed in the title bar of the dialog box. If we omittitle the application name is placed in the title bar.

InputBox : Displays a prompt in a dialog box waits for the user to input text or click a

button and returns a string containing the contents of the text box.

Syntax :

InputBox (prompt[,title])

Prompt Required : String expression displayed as the message in the dialog box. The

maximum length of prompt approximately 1024 characters depending on the width of the

characters used.

Title (Optional) : String expression displayed in the title bar of the dialog box. If we omit

title the application name is placed in the title bar.

25) What are menus ? Explain the various types of Menus ?

Visual Basic provides a feature that increases the functionality of an application byadding the menu bar. Once these menus are created they can be individually programmed

to respond when selected. Another type of menu that has become popular with users is

the pop-up menu. This menu can be very specific to certain control areas of theapplication . Pop-up menu is also referred to as context sensitive menus.

Menu bars are used in applications to provide an organized collections of commands thatcan be used by the user. In visual basic there are two different methods to create menus-

first is the built in menu editor dialog box. It provides an easy and simple way to generate

menus. Once created all menu objects can set their properties through the program code.Another method used to create menus in Visual Basic involves using the Win32

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application programming interface. The win32 API is a series of functions that are

extremely called by Visual Basic and are provided by the operating system.

Types of Menus

Drop Down Menus

The menu that have a single level menu.

Nested Menus

The nested menus can be created the way we have created normal menus by simply

adding new to the list and shifting them to the right of the one we want them to be nested.

Pop Menus

These are also context menus and it provides the user another way to control theapplication. In Excel the user has the option to use the main menu bar or shortcut keys or

pop-up menus. These menus are created as part of the main menu system but they arevisible only when they are needed and invoked through program code.

Properties of Menus

Property Description

Caption The text of the menu that the user will see

Name The name that we will use in our code to refer to this menu and toidentify the event code for each menu item

Index Used to from menu control arraysShortcut The menu can be invoked either by clicking it with the mouse in a

normal way or by pressing the short cut key.

Visible Clicking the check box to set this property to true causes the menu

item to be visible at run time

Enabled If this is clicked or set to true , then the user can select the menu

item setting it to false by clearing the check box causes the menu

item to appear the grayed out meaning the user cant select it

26) What are Errors ? Explain its types.?

Even though we design and code the programs with utmost care run time errors canalways occur in our program. A run time errors can occur when the user tries to open afile when the file does not exist or when we tries to read from the disk without inserting

a disk in the floppy drive. Visual Basic does not handle errors automatically . It simply

notifies our program of the error. A good programmer will always handle the error in the

code to provide understandable information to the user , allow the user to correct a valuea value and retry an operation or exit the program.

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When our code and run the programs, we might encounter three types of errors :

Syntax Errors: When code is constructed incorrectly Syntax error occurs. An incorrectlytyped keyword, omission of required punctuation or an incorrect construct such as Next

statement without a corresponding For statement.

Run Time Errors: A run time error occurs at the time of running a program. Forexample if the program tires to open a file that does not exist or the user forgets to put a

floppy disk in the floppy disk drive. If a run time error occurs and the program contains

code for handling that error. Visual Basic displays a message and lets us enter the debugmode or Help or end the application.

Logical Errors: It usually occurs when an application does not perform the way it

should. It may contain syntactically valid code. Finding logical errors is especiallydifficult . The programmer needs to verify and analyze the results to trap the logical

errors.

27) What is 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 tracing

what is happening in the application while it is running, it also helps in diagnosing theprogram errors as you write through its automatic syntax checker and various other tools

which help in remembering the keywords and syntax as you type in the code.

28) What is Visual Database Architecture ?

A Visual Database application consists of three components :1. User Interface and Application code-it is the part what the user interacts with. It

contains forms that display the data enable the user to view or update it

2. Database Engine-This part is contained in a set of Dynamic Link Library files and

is linked to our Visual Basic program at run time. The engine is responsible forreading and modifying the database. Data store is the file or files containing the

database tables. A database application can be categorized into two types :

Client Server is a system which both the database engine and the datastore are located on a central server. Multiple client applications can

simultaneously request the services of the engine. The engine can access

the data store and return the requested records to local application.

Remote is a system in which database engine resides on the samecomputer as the user application while the data store is located on a

remote machine.

3. Programmatically, using Visual Basic Data Access Object (DAO) Creatingdatabase programmatically using Data Access objects gives our program

complete control how the database is created and structured.

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4. Using the Visual Data Manager application provided with Visual Basic Using

this Visual Basic add-in one can create databases, as well as create , modify and

delete tables , indexes and relations with a database.5. Using Microsoft Access This tool is probably the most widely used to create Jet

databases. It provides the added advantage of enabling us to create queries and

relations using a Visual drag and drop interface6. Using the Third party database management programs Many other programs ,

both commercial and shareware are available to manage Jet and other types of

database. Some are highly specialized where as others general purpose ultimatelike Visual Data manager.

29) What is Data Manager ?

The Data manager is Visual application included with Visual Basic that we can use to

create a Jet Database. Once the database is created, we can manipulate it using data

controls and data access objects.

30) What is Data control ? Define Tables, Fields, records.

The data control provides a relation interface to database files, Basically a relational

database is one that stores data of tables made up of columns and rows of data. In Visual

Basic columns are referred to as fields and rows are referred to as records. The MicrosoftJet Database engine that powers the data control view all database as a set of relational

tables, regardless of their physical file format. This means that when we use data from

external databases (Such as Foxpro and Oracle), we can use the same relational terms.

Tables : A table is a logical grouping of related information arranged in rows and

columns similar to a spreadsheet table. For example a table might contain a list ofinformation about authors such as their names, date of birth, addresses etc.

Fields : Each column in a database table is called a field. Tables are defined by

the fields they contain with each field describing the data it is to hold. When

creating a database we assign a data type, maximum length and other attributes toeach field. Fields can contain characters , numbers or even graphics.

Records : It is a collection of fields

31) What is Structured Query Language ?

Once the data is stored in the database , retrieving it is made easier by using an Englishlike language called Structured Query Language (SQL). It has evolved into the most

widely accepted means to converse with a database. Basically the user asks a question

in the SQL language, this question is called a query. The database engine answers byreturning any database rows that meet the requirements of the query. The query usually

contains the names of the tables to search, the names of the columns to return and other

information that sets the scope of the search.

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32) What is Data control ? Explain the concept of Databases in details ?

What the user can perform with the help of data control ?All business applications need to store large volumes of data organized in a format so thatinformation can be retrieved efficiently and quickly as and when required. With the help

of a DBMS (Database Management System) managing data becomes easy. A DBMS is a

system that manages the storage and retrieval of data in a database. It helps theprogrammer in concentrating on managing information. Microsoft Visual Basic provides

tools for creating and accessing a variety of Relational Database Management System

(RDBMS). An RDBMS stores and retrieve information according to a set of definedrelationships. In an RDBMS the database is the container of tables in which all data is

stored and the relationships are formed by data values.

A database is a collection of data that are related to one another to support a commonapplication. Employee details, Names and addresses- each of these collections of data

constitutes a database. In a database data is organized and stored in a table comprising of

rows and columns. Rows in a table are called records and columns are called fields. Each

record in a table has a unique key field that identifies it and are used to link with other

tables. This key field is termed as Primary key. The primary key of a table is added as afield in another table to establish the relationship between the two tables and it becomes a

Foreign Key in the second table. For example employee records have employee numberand department record have department number both in employee table and in the

department table. In the employee table the primary key is employee number and foreign

key is deptno.

The Data control can perform the following task without the use of code :

Connect to a local or remote database

Open a specified database table or define a set of records based on Structured

Query Language (SQL) query of the tables in that database.

Pass data fields to bound controls, where we can display of change the values Add new records or update a database based on any changes we can make to data

displayed in the bound controls.

Trap errors that occur as data is accessed

Close the database.

33) What are the Various categories of accessing database is available in

Visual Basic ?

Visual Basic can access three categories of databases:

1. Jet Databases: Databases are created and manipulated directly by the Jet engine.The Jet engine is the data manager component of Microsoft Access and Visual

Basic

2. ODBC (Open Database Connectivity ): Visual Basic also allows access to adatabase on a Network. These include client server databases that conform to the

ODBC standard such as oracle. Most databases that support ODBC can be

accessed.

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3. Indexed Sequential Access Method (ISAM) Databases: ISAM databases include

dbase, Microsoft Visual Foxpro and Paradox.

34) What is Data Access Object Model ? Explain in detail

The Data Access Object Model is an object oriented interface to the Jet database engine.The DAO model is a collection of object classes that corresponds to the structure of a

relational database system. Each of these classes provides properties and methods that

allow us to perform like creating databases, defining tables, fields and indexes andestablishing relations between tables, querying the database. At the top of the hierarchy is

the DBEngine object that represents the Microsoft Jet Database engine. The DBEngine

object contains and controls all other objects in the hierarchy of data access objects. It has

a collection called workspaces, which contain one or more workspace objects. TheWorkspace object defines a session for the user. In a session one can open multiple

databases, managing transactions and establish a security level. By default the Jet engine

creates a Workspace object DBEngineWorkSpace(0) Additional workspace objects can

be created if required . Each workspace has a user ID and a password associated with it.Each workspace has a database collection contains one or ore Database objects. Each

database object has TableDefs collection which contain one or more TableDef object andso on.

35) What is Recordset ? Explain the various types of Recordset.

Recordset is an object that contains a set of records from the database. Using a Recordset

object one can programmatically manipulate the data in a database. There are three types

of Recordset objects

1. Tables type Recordset: The table type Recordset object is a set of records thatrepresents a single table that represents a single table that can use to add, changeor delete records. One cannot create a table-type Recordset on an attached table.

An attached table is another table in another database. Some operations such as

indexing and using the seek method are only allowed on a table type Recordset.Table are the fastest type of Recordsets.

2. Dynaset type Recordset: The dynaset-type recordset object is a set records that

represents or attached tables or the results of queries containing fields from one ormore tables. A dynaset contains keys to the underlying tables. A dynaset enables

us to extract and update data from more than one table.

3. Snapshot-type Recordset: This object is a fixed set of records that one can use to

find data or generate reports. A snapshot type Recordset can refer to any table,attached table or query. A snapshot cannot be updated and does not reflect

changes to data made by other users.

36) Explain the Data Access methodology in context to Visual Basic ?

Today companies building database solutions face a number of challenges as they seek togain maximum business advantage from the data and information distributed throughout

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their corporations. Universal Data Access provides high performance access to a variety

of information sources, including relational and non relational and an easy to use

programming interface that is tool and language independent. These technologies enablecorporations to integrate diverse data sources, create easy to maintain solutions and use

their choice of best of breed tools, applications and platform services. Universal Data

Access is based on open industry specifications with broad industry support and workswith all major established database platforms.

Universal Database Access Architecture (UDA)

The strategy of UDA is to enable developers to access diverse types of data, from both

relational and non relational data sources. Non relational data sources are data such as

email , Internet explorer and file systems.

The UDA architecture consists of three kinds of database components : Providers ,

Services and Consumers

Data Providers:

Data providers are components that represent data sources such as SQL databases,

indexed sequential files and spreadsheets. ActiveX Data objects uses general OLE DB

providers to access unique features of specific data sources. It also uses native OLE DB

providers including a specific OLE DB provider that provides access to Open DatabaseConnectivity drivers

Service Components:

These components provide an interface between the Data providers and Data consumers.

The service components process the data and transmit OLE DB data to data consumers.They consist of Cursor Engine and Query Proceessor

Data Consumers:

The Data consumers can be an application written in Visual Basic or VC++ or Java

which can consume OLE DB data. For example an application written in Visual Basic

that displays the data after retrieving it using ADO is a data member.

37) What are various components of Microsoft Data Access?

The Microsoft Data Access Components is the practical implementation of UniversalData Access

1. ODBC: Open Database Connectivity is a widely used accepted applicationprogramming interface (API) for database access and it uses Structured Query

Language (SQL) as its database access language.

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2. OLEDB: OLEDB is a set of interfaces for efficient access to Microsoft and third

party data stores. It provides an open standard for accessing and manipulating all

types of data.

38) What are ActiveX Data Object ? Explain in Detail

ADO is Microsofts strategic high level interface to all kinds of data. ADO provides

consistent , high performance access to data, whether we are creating a front end database

client or middle tier business object using an application, tool , language or even anInternet browser. ADO is the single data interface we need to know 1-to n-tier client

server and web based data driven solution development.

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Remote Data Services

It is a feature of ADO. RDS delivers a new Web data access technology that allows

developers to create data-centric applications within ActiveX-enabled browsers such asMicrosoft Internet explorer. It is a service used to transport ADO recordsets from a server

to a client computer. The resulting recordset is cached on the client computer and

disconnected from the server.

The future of data access is ADO. Its goal is to supersede the Data Access Object

(DAO), and Remote Data Object (RDO) models by providing flat and easy to learnobject hierarchy that is similar to the other objects used in DAO and RDO.

The ADO model is flat and small unlike other programmable object models, which rely

on the hierarchy to provide order and structure. The ADO object model consists of sevenobject and four collections, each of which has very specific role relating to the

functionality of the service provider.

39) What is an ADO object and Explain it in detail?

ADO object comprises of the following objects:

Connection Object: A connection object is used to establish a connection to a data source

based on the information that includes the connect string, username and password, cursortype and location , time-out values etc.

Command Object: A command object adds, deletes or updates data in the data source or

retrieves data. It stores information about a SQL command or reference to a stored

procedure. Parameterized commands are also available that allow the values in the queryto be changed at runtime

Recordset object: A Recordset object represents the entire set of records from a base tableon the result of an executed command. At any time the Recordset object refers to only asingle record within the set as the current record. All the recordset objects are constructed

using records and fields . When we use ADO, we manipulate data almost entirely using

recordset objects.The Recordset is the primary means of examining and modifying data in the rows. The

Recordset object allows us to:

1. Specify which rows are available for examination

2. Traverse the rows3. Specify the order in which the rows may be traversed

4. Add, change or delete rows

5. Update the data source with changed rows6. Manage the overall state of the Recordset.

40) Write short notes ADO Collection and ADO Events

ADO Collection: ADO provides collections, a type of object that contains other objects

of a particular type. The objects in the collection can be retrieved with a collection

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method either by name, as a text string, or by ordinal as an integer. ADO provides four

types of collections:

1. Errors Collection: The collection object has the Errors collection which containsall Error objects created in response to a single failure involving the data source.

It contains all of the extended information about the error that is available from

the OLE DB service provider. Any operation involving ADO objects can generateone or more errors. As each errors occurs one or more error objects can be placed

in the Error collection of connection object. When another ADO operation

generates an error, the Errors collection is cleared and the new set of Error objectscan be placed in the Errors collection.

2. Parameters Collection: The Command object has the Parameters collection

which contains all Parameters objects that apply to that command object. Often

commands require variables parts parameters that can be altered before we issuethe command.

3. Fields Collection: A row of Recordset consists of one or more fields. If we vision

the Recordset as two dimensional grid, the fields line up to form columns. Each

field has among its attributes a name, a data type and a value. It is this value thatcontains the actual data from the data source. A Field is also one of the objects in

the object model.4. Properties collection: A properties collection contains all the property objects for

a specific instance of an object.

ADO Events: ADO 2.0 introduces the concept of events to the programming model.Events are notifications issued by certain operations that an operation is about to occur,

or has already occurred. An event is actually a call to an event handler routine that we

define in our application. Event handlers called before the operation starts offer you theopportunity to examine or modify the operation parameters then either cancel or allow

the operation to complete. Event handlers called after an operation completes notify you

at the completion of an asynchronous operation.

41) Difference between DAO, RDO and ADO objects

DAO RDO ADO

DBEngine RdoEngine -

Workspace rdoEnvironment -

Database (Connection for

ODBCDirect workspace)

rdoConnection Connection

TableDef rdoTable -

QueryDef rdoQuery CommandRelation - -

Recordset rdoResultSet Recordset

Field rdoColumn Field

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42) What is an Array ? Explain its various types ?

Arrays are used to refer to a serie

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