Intro_to_VB.PPT

Developed by :Abhijeet
Visual
Basic
An Introduction

What is Visual Basic?
 Visual Basic is event-driven. It means that the
code is executed in response to some event
such as clicking a button, selecting a menu
item, loading a window etc. Nothing happens
until an event is detected. Once an event is
detected, the code corresponding to that event
(event procedure) is executed. Program control
is then returned to the event processor.

Visual Basic: Background
 3rd Generation Languages (Procedural)
Use English-like statements (COBOL, Fortran)
 BASIC
Beginner’s All-purpose Symbolic Instruction
Code
Created in 1963 to teach programming with a
limited set of reserved words
In 1975, Bill Gates and Paul Allen developed a
version of Basic that ran in 4K RAM on the Altair
1981 – Basic was default user-interface on IBM-
PCs
1991 – Microsoft introduced Visual Basic

Visual Basic: Background
(cont’d)
 Microsoft “Visual Basic” (VB)
Modified to work within “Windows”
environment
Kept programming language
Added visual text editor
Added graphical “controls” (e.g., command
buttons, check boxes, etc.)

Features of Visual Basic
 It has a full set of controls (labels, text
boxes, list boxes)
 Use of Mouse and keyboard actions.
 It supports string handling and graphics
functions.
 It supports sequential and random
access file support.
 It provides powerful database access
tools.

VB Development Environment
 Integrated Development Environment
Includes all tools needed to develop and
TEST program
 Event-driven: Events are actions that
result from end-user activity
 Object-oriented: Each control is an object
with:
Properties (set in property palette)
Methods (predefined set of actions)

VB Development Environment
(cont’d)
 Project window includes:
Project Explorer (hierarchical list of forms and
modules – view code or view object
Form Module(s)
Code Module(s)
Properties
Toolbox
Other information …

Visual Basic: Files
 VBP file (“project” file)
 Text file: Names of other files in project, info
about the VB environment (e.g., version)
 FRM file (“form” file)
 One .frm file for each form in project
 Can have multiple forms
 VBW (“workspace” file)
 Holds info about forms and development
environment

Terms
 Forms Windows that you create for
use interface
 Controls Graphical features drawn on
forms to allow user interaction
 Objects Forms and Controls are
objects.
 Properties: Every characteristic of a form
or control is specified by a property.
 Methods Build-in procedure that can be
invoked to impart some action to a particular
object

The VB
Environment

The Toolbox
&
Controls

3-step process for
writing a VB project
1. Design the user interface
2. Define the properties
3. Write the code

 Project Explorer Window
Lists the forms, and modules in your current
projects.
 Properties Window
Properties Window is used to assign and
display the different properties of control

Writing
the code

Writing the code
• You can add code to an object by double-clicking
on that object.
• You can also add code by choosing code under
the view menu.

Assignment
Statements

Assignment Statements
• The assignment statement assigns a value to a
property or variable.
• Assignment statements operate from right to left
• That is, the value appearing on the right side of
the equals sign is assigned to the property named
on the left.
• You should read the equals sign as “is assigned
the value”

lblTitle.Caption = “My First Program”
Assignment Statements
Object Name
Property Value
Period Is assigned the value

Comments

Comments
• Comments are statements which are not executed when
the program runs.
• The purpose of comments are to explain your
programming code
• VB comments begin with an apostrophe
• In the general declarations of each form put the program
name, your name, date, & a brief description
• Every procedure or function should have a brief description
as to its purpose.
• Every variable used must be commented.

Variables
&
Constants

Variables
A variable is a location in memory where data is
stored.
A variable holds the data assigned to it until a new
value is assigned or the program is finished.
Variables can be changed throughout a program

Constants
A constant is also location in memory where data
is stored.
However, a constant cannot change throughout a
program.

Data Types
The data type of a variable or constant indicates
what type of information will be stored in the
allocated memory space.
Some common data types include :
• Currency (decimal fractions, dollars & cents)
• Integer (whole numbers)
• Double (numbers w/ 14 digits of accuracy)
• Single (numbers w/ 6 digits of accuracy)
• String (letters, digits, & other characters)

When you declare a variable or a named constant,
VB reserves an area of memory and assigns it a
name, called an identifier.
Declarations
The declaration statements establish your
project’s variables and constants, give them
names, and specify the type of data they will hold.
To declare a variable use Dim statement
To declare a constant use Const statement

Declaring a variable
Dim iCount As Integer ‘declare an integer variable
Declare a variable
Variable Name or
Identifier
Data type prefix
Variable Name
Data Type
Comment

Declaring a constant
Const cRate As Currency ‘declare a constant
Declare a constant
Constant Name or
Identifier
Data type prefix
Constant Name
Data Type
Comment

Functions

Functions
A function performs an action and returns a value.
VB supplies many built in functions you can use in
your programs.
The expression to operate upon, called the
argument(s), must be enclosed in paretheses.

Function Example
Val (txtQuantity.Text)
Function
Argument

Function Example Cont’d
Functions cannot stand by themselves. Functions
return values which can be used as part of a
statement.
iQuantity = Val (txtQuantity.Text)
Argument
Function
Is assigned the
value
Variable

Some
built-in
Functions

Val Function
The Val function converts text into a number.
iQuantity = Val (txtQuantity.Text)
Val (ExpressionToConvert)

Format Function
The Format function controls the way output is
displayed
lblGst.Caption = Format$(cGst, "Currency")
Format[$] (ExpressionToFormat [, “Description”])

+ Plus
- Minus
* Multiply
/ Division
( Opening parenthesis
) Closing parenthesis
^ Power
Mathematical Operators

Intro_to_VB.PPT

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