chapter 3 - visual basic schneider chapter 3-a fundamentals of programming in visual basic

Chapter 3 - Visual Basic Schneider

Chapter 3-A

Fundamentals of Programming in

Visual Basic


Outline and Objectives

Visual Basic Objects Visual Basic Events

Numbers Strings Input/Output Built-In Functions


The Initial Visual Basic Screen

Toolbox

Project Explorerwindow

Properties window

Form

Menu bar

Description pane

Form Layout window

Toolbar

Project Container window


Steps to Create a Visual Basic Program

1. Create the interface by placing controls on the form

2. Set properties for the controls and the form

3. Write code for event procedures associated with the controls and the form


Four Useful Visual Basic Controls

Text Boxes Labels

Command Buttons Picture Boxes


Placing a Text Box on a Form

Double-click on the text box icon in the toolbox to add a text box to your form

Activate the properties window (Press F4)

Set values of properties for text box


Placing a label on a Form


Some Useful Properties of Objects

Name

Caption Text (for Text Boxes) BorderStyle Visible BackColor Alignment Font


Naming Objects:

Use the Property window to change the Name property of an object

Good programming practice dictates that each object name begins with a three letter prefix that identifies the type of object.


Naming Objects:

Object Prefix Example

Command Button cmd cmdStart

Form frm frmPayroll

Label lbl lblName

Picture box pic picClouds

Text box txt txtAddress

Naming Objects

An Object Name•Must Start with a letter

•Can include numbers and underscore (_)

•Cannot include punctuation or spaces

•Can be a maximum of 40 characters



Visual Basic Events

Code is a set of statements that instruct the computer to carry out a task.

Code can be associated with events When an event occurs, the code

associated with that event (called an Event Procedure) is executed.


Creating An Event Procedure

Double-click on an object to open a Code window. (The empty default event procedure will appear. Click on the Procedure box if you want to display a different event procedure.)

Write the code for that event procedure.


Example of An Event Procedure

Private Sub objectName_event ( ) statementsEnd Sub

Private Sub Text2_GotFocus( ) Text2.Font.Size = 12 Text2.Font.Bold = False

Text2.forecolor=vbRedEnd Sub


More Examples

Private Sub cmdButton_Click( ) txtBox.ForeColor = vbRed txtBox.Font.Size = 24 txtBox.Text = “Hello”End Sub

Exercises: What is wrong??!


A. Private Sub cmdButton_Click( )

frmHi= “Hello”

End Sub

B. Private Sub cmdButton_Click( )

txtOne.ForeColor= “red”

End Sub

Exercises: What is wrong??!


C. Private Sub cmdButton_Click( )

txtBox.Caption = “Hello”

End Sub

D. Private Sub cmdButton_Click( )

txtOne.MultiLine= True

End Sub

Tips

Most Properties can be set or altered at run time with code.

cmdButton.visible = False The MultiLine property of a text box

can only be set from the properties window, also the Name property….

“” surrounds Caption, Name, Font.Name or strings. Not True for vars or numeric constants


Color Constants


• At design time colors are selected from a palette

• At run time the eight most common colors can be assigned with the color constants:

vbBlack vbMagentavbRed vbCyanvbGreen vbYellowvbBlue vbWhite


Components of Visual Basic Statements

Constants Variables Keywords (reserved words)


Constant

Can NOT change during the execution of a program.

Types of Constants:•numeric constants

•string constants


Valid Numeric Constants:

Integer Real number

-2987 -1900.05

16 0.0185

5 10.56


Invalid Numeric Constants:

14,005.5 6.8% 33- $190.04 15 78 3.5&


Arithmetic Operations

Operator Operation Basic expression

^ Exponentiation A ^ B

* Multiplication A * B / Division A / B + Addition A + B - Subtraction A - B

Scientific Notation


10n=1000...0103=1000

10-n=0.000...01 10-3=0.0001

b.10±r VB Notation bE±r

1.4 * 10-45

14 * 10 ^-45

1.4E -45 1.4E -44


String Constants:

A sequence of characters treated as a single item

The characters in a string must be surrounded by double quotes (“ ”)


Valid String Constants

“A rose by any other name”“9W”“134.23”“She said, ‘stop , thief!’ ”


Invalid String Constants

‘Down by the Seashore’“134.24“She said, “Stop, thief!””


Variables

A storage location in main memory whose value can be changed during program execution.

These storage locations can be referred to by their names.

Every variable has three properties: a Name, a Value, and a Data Type.

Types of variables: Numeric and String


Rules for Naming Variables

Must begin with a letter Must contain only letters, numeric

digits, and underscores ( _ ) Can have up to 255 characters VB is insensitive for uppercase or

lowercase Cannot be a Visual Basic language

keyword (for example, Sub, End, False)


Valid Variable Names:

timeElapsed a1b2c3 Var_1 n celsius


Invalid Variable Names:

maximum/average 1stChoice square yard Name?


Keywords

Words that have predefined meaning to Visual Basic .

Can Not be used as variable names. Examples:

•End - Print

•Sub - Let

•If -Select

•While -Call


Numeric Variables

Used to store numbers Value is assigned by a statement of the

form:

numVar = expression

The variable must be on the left and the expression on the right.


Assignment Statement:

The statement var = expr assigns the value of the expression to the variable

tax = 0.02 * (income - 500 * dependents)

sum = 2 + x + 4.6 + y


Valid Assignment Statements

count = count + 1 num = 5 count = count + num /2


Invalid Assignment Statements

10 = count count + 1 = count


String Variables

A string variable stores a string. The rules for naming string variables

are identical to those for naming numeric variables.

When a string variable is first declared, its value is the empty string.


Visual Basic Print Statement

Print is a method used to display data on the screen or printer.

Can be used to display values of variables or expressions


Examples of Print Statements

Private Sub cmdCompute_Click()

picResults.Print 3 + 2 picResults.Print 3 - 2 picResults.Print “3 * 2” picResults.Print 3 / 2 picResults.Print 3 ^ 2 picResults.Print 2 * (3 +

4)End Sub



speed=3taxRate=speed+5total=30picOutput.Print speedpicOutput.Print taxRatepicOutput.Print “Class average is”; total/3

3

8

Class average is 10



x = 15 y = 5picOutput.Print (x + y) / 2, x / y

Output: 10 3


String Variable Example

Private Sub cmdShow_Click() picOutput.Cls phrase = "win or lose that counts." picOutput.Print "It's not whether you ";

phrase picOutput.Print "It's whether I "; phraseEnd Sub


Concatenation

Two strings can be combined by using the concatenation operation.

The concatenation operator is the ampersand (&) sign.

Example

&: is always used to make concatenation

+: makes concatenation when it is used with strings, and as summation with numbers

What about “hi”+5 ???


Examples of Concatenation:

strVar1 = “Hello”strVar2 = “World”picOutput.Print strVar1& strVar2

txtBox.Text = “32” & Chr(176) & “ Fahrenheit”

Chr() & Asc()

The characters have numbers associated with them, these values called ANSI values of characters

Chr(65) = A Chr(66) = B Chr(97) = a Chr(176) =

•Asc(A) = 65•Asc(B) = 66•Asc(a) = 97•Asc( ) = 176

Val, Str Val (“23”) = 23 Val (23) =23 Str (23) = Val (“50” + “60”) = Val (“5060”) = 5060 Val (“50”) + Val(“60”) = 50+60=110 Val(“Hi”) = 0 Val(“89Hello”) = 89 Val(“89Hi10”) = 89 Str("10") + Str("50") = Str(“Hello”) error

10 50

space

23


Declaring Variable Types

Use the Dim statement to declare the type of a variable.

Examples: Dim number As Integer Dim flower As String

Dim interestRate As Single


Data Types

Single: a numeric variable that stores real numbers (0 By default)

Integer: a numeric variable that stores integer numbers (from -32768 to 32767) (0 By default)

String: a variable that stores a sequence of characters (“”empty string By default)

Boolean: a variable that stores True or False (False By default)


Using Text Boxes for Input/Output

The contents of a text box are always a string type.

Numbers can be stored in text boxes as strings.


Using Text Boxes for Input/Output

The contents of a text box should be converted to a number before being assigned to a numeric variable.

Val(txtBox.Text) gives the value of a numeric string as a number

Example: Dim numVar as Single numVar = Val(txtBox.Text)

The contents of a text box is always a string

Numbers types into the text box are stored as strings. Therefore, they should be converted to numbers before being assigned to numeric.


Example

Example 1xString=“528”xValue=Val(xString)

xValue=528Example 2yValue=428yString=Str(yValue)

yString=“428”

“528”

528

xString

xValue

428

“428”

xValue

xString


Program Documentation

An apostrophe (') is used to indicate that the remainder of the line is a comment. (Comments are ignored by Visual Basic.)

Remarks can appear on a separate line or following a Visual Basic statement.

chapter 3 - visual basic schneider chapter 3-a fundamentals of programming in visual basic

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