introducing visual basic…...initial visual basic screen chapter 3 - vb 2005 by schneider 10...

Chapter 3 - VB 2005 by Schneider 1

Introducing Visual Basic…

September 8, 2006

Today…

• Chapter 3 provides a great walkthroughintro to VB

• We’re going to take a detailed look at thistoday (and pick it up next week)…

• We’ll keep the pace even, but feel free tooffer feedback to the prof……we can always adjust as necessary

depending on the needs of the class!

Next week…

• Kim’s going to be back• She’ll keep going with today’s material

(and a quick recap)• Be prepared for your first assignment

later next week…• Also, Kim will get the website up this

weekend!• She promises… ;)

Chapter 3 – Fundamentals ofProgramming in Visual Basic

• 3.1 Visual Basic Controls

• 3.2 Visual Basic Events

• 3.3 Numbers

• 3.4 Strings

• 3.5 Input and Output

3.1 Visual Basic Controls

• Invoking Visual Basic

• Text Box Control

• Button Control

• Label Control

• List Box Control

• Name Property

• Fonts / Auto Hide

• Positioning and Aligning Controls

Visual Basic Start Page

Start a New Project

New Project Dialog Box

Initial Visual Basic Screen

Toolbox

3 Ways to Place a Control from theToolbox onto the Form Window

• Double-click

• Drag

• Click, Point, and Drag

Four Controls at Design Time

Text box

To select a control, click on it. Sizing handleswill appear when a control is selected.

Text Box Control

• Used for input and output

• When used for output, ReadOnlyproperty is set to True

Sizing handles

Tasks button

Properties Window

Categorized view Alphabetical view

Press F4 todisplay theProperties

window for theselected control.

Properties Window

PropertiesSettings

Selectedcontrol

Some Often Used Properties

• Text

• Autosize

• Font.Name

• Font.Size

• ForeColor

• BackColor

• ReadOnly

Setting Properties

• Click on property name in left column.

• Enter its setting into right column bytyping or selecting from optionsdisplayed via a button or ellipses (…).

Setting the ForeColor Property

1. Click on ForeColor.

2. Click on button at rightof settings box.

3. Click on Custom tab toobtain display shown.

4. Click on a colour.

Font Property1. Click on Font in

left column.

2. Click on ellipsisat right ofsettings box toobtain displayshown,

3. Makeselections.

Button Control

• The caption on the button should indicatethe effect of clicking on the button.

• Text property determines caption.

Add an "access key"

Label Control

• Used to identify the contents of a text box.

• Text property specifies caption.

• By default, label automatically resizes toaccommodate caption on one line.

• When the AutoSize property is set to False,label can be resized manually. Used primarilyto obtain a multi-rowed label.

List Box Control

• Initially used to display several pieces ofoutput.

• Later used to select from a list.

The Name Property• How the programmer refers to a control in

code• Setting for Name property near top of

Properties window.• Name must begin with a letter, be less than

215 characters long, and may include numbersand letters.

• Use appropriate 3- or 4-character namingprefix

Control Name Prefixes

lstOutputlstlist box

txtAddresstxttext box

lblAddresslbllabel

btnComputebtnbutton

ExamplePrefixControl

Renaming the Form

• Initial name is Form1

• The Solution Explorer window lists a filenamed Form1.vb.

• To rename the form, change the name ofthis file to newName.vb

• newName should begin with prefix frm.

• Proportional width fonts take up lessspace for "I" than for "W" – like MicrosoftSans Serif

• Fixed-width fonts take up the sameamount of space for each character –like Courier New

• Fixed-width fonts are good for tables.

Auto Hide

• Hides Toolbox when not in use

• Vertical push pin icon indicates auto hide isdisabled.

• Click the push pin to make it horizontal andenable auto hide.

Push pin

Positioning Controls

Proximityline

Aligning Controls

Snap line

Aligning Controls

Snap line

3.2 Visual Basic Events

• An Event Procedure Walkthrough

• Properties and Event Procedures of theForm

• The Header of an Event Procedure

• An event is an action, such as the userclicking on a button

• Usually, nothing happens in a VisualBasic program until the user doessomething and generates an event.

• What happens is determined bystatements.

Sample Statements

• txtBox.ForeColor = Color.Red

• txtBox.Visible = True

• txtBox.Text = “Hello World”

General Form:

controlName.property = setting

Sample Form

txtFirst

txtSecond

btnRed

• When you click on a text box, a cursorappears in the text box, and you can typeinto the text box.

• Such a text box is said to have the focus.

• If you click on another text box, the first textbox loses the focus and the second text boxreceives the focus.

Examples of Events

• btnShow.Click

• txtBox.TextChanged

• txtBox.Leave

General Form:

controlName.event

The three steps in creating aVisual Basic program:

1. Create the interface; that is, generate,position, and size the objects.

2. Set properties; that is, configure theappearance of the objects.

3. Write the code that executes whenevents occur.

Code Window

MethodNamebox

ClassNamebox

Page tab

Structure of an Event Procedure

Private Sub objectName_event(...) Handles objectName.event statements End Sub

(...) is filled automatically with(ByVal sender As System.Object, ByVale As System.EventArgs)

Header

Code Window

MethodNamebox

ClassNamebox

Page tab

Create an Outline for an EventProcedure; i.e. header and End Sub

1. Double-click on a control or2. Use the Class Name and Method Name boxes.

(We primarily use the first method.)

Sample Form

txtFirst

txtSecond

btnRed

Double Click on txtFirst

Code for WalkthroughPublic Class frmDemo Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged

End SubEnd Class

Code for WalkthroughPublic Class frmDemo Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.Blue End SubEnd Class

IntelliSense

Automatically pops up to give the programmer help.

Code Window

Click tab to return to Form Designer

Sample Form

txtFirst

txtSecond

btnRed

Double-click on btnRed

Code for WalkthroughPublic Class frmDemo Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.Blue End Sub

Private Sub btnRed_Click(...) Handles btnRed.Click

End SubEnd Class

Code for WalkthroughPublic Class frmDemo Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.Blue End Sub

Private Sub btnRed_Click(...) Handles btnRed.Click txtFirst.ForeColor = Color.Red End SubEnd Class

Event Procedure txtFirst.Leave

• Select txtFirst from Class Name boxdrop-down list.

• Select Leave from Method Name boxdrop-down list.

Code for WalkthroughPrivate Sub txtFirst_Leave(...) Handles txtFirst.Leave

End Sub

Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.BlueEnd Sub

Private Sub btnRed_Click(...) Handles btnRed.Click txtFirst.ForeColor = Color.RedEnd Sub

Code for WalkthroughPrivate Sub txtFirst_Leave(...) Handles txtFirst.Leave txtFirst.ForeColor = Color.BlackEnd Sub

Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.BlueEnd Sub

Private Sub btnRed_Click(...) Handles btnRed.Click txtFirst.ForeColor = Color.RedEnd Sub

Header of Event ProcedurePrivate Sub btnRed_Click(…) Handles btnRed.Click

Identifies eventName, canbe changed.

Private Sub Button_Press(…) Handles btnRed.Click

Handling Multiple Events

Private Sub Button_Click(...) Handles btnRed.Click, txtSecond.Leave txtFirst.ForeColor = Color.RedEnd Sub

Event procedure can be invoked by two events.

Altering Properties of the Form

• The following won't work:frmDemo.Text = "Demonstration"

• The form is referred to by the keyword Me. Me.Text = "Demonstration"

3.3 Numbers

• Arithmetic Operations

• Variables

• Incrementing the Value of a Variable

• Built-In Functions:• Math.Sqrt

• Int

• Math.Round

Numbers continued

• The Integer Data Type

• Multiple Declarations

• Parentheses

• Three Types of Errors

Arithmetic Operations

• Numbers are called numeric literals

• Five arithmetic operations in Visual Basic• + addition

• - subtraction

• * multiplication

• / division

• ^ exponentiation

Numeric Expressions

• 2 + 3

• 3 * (4 + 5)

• 2 ^ 3

Displaying Numbers

Let n be a number or a numeric expression.

The statement lstBox.Items.Add(n)displays the value of n in the list box.

Example 1: Form

Example 1: Code and OutputPrivate Sub btnCompute_Click (...) Handles btnCompute.Click lstResults.Items.Add(5) lstResults.Items.Add(2 * 3) lstResults.Items.Add((2 ^ 3) – 1)End Sub

Output 5in list 6box 7

Example 1: Code using WithPrivate Sub btnCompute_Click (...) Handles btnCompute.Click With lstResults.Items .Add(5) .Add(2 * 3) .Add((2 ^ 3) – 1) End WithEnd Sub

Numeric Variable

A numeric variable is a name to which anumber can be assigned.

Examples:

speeddistance

interestRatebalance

Variables

• Declaration:Dim speed As Double

Variable name Data type

• Assignment:speed = 50

Initialization

• Numeric variables are automaticallyinitialized to 0:Dim varName As Double

• To specify a nonzero initial valueDim varName As Double = 50

Numeric Expressions

Numeric variables can be used in numeric

expressions.

Dim balance As Double = 1000lstBox.Items.Add(1.05 * balance)

Output: 1050

Assignment Statement

Dim numVar1 As Double = 5Dim numVar2 As Double = 4numVar1 = 3 * numVar2lstBox.Items.Add(numVar1)

Output: 12

Incrementing

• To add 1 to the numeric variable varvar = var + 1

• Or as a shortcutvar += 1

• Or as a generalizationvar += numeric expression

Built-in Functions

• Functions return a value

Math.Sqrt(9) returns 3

Int(9.7) returns 9

Math.Round(2.7) is 3

Integer Data Type

• Variables of type Double can be assignedboth whole numbers and numbers withdecimals.

• The statement Dim varName As Integer declares a numeric variable that can only be assigned whole number values

between about -2 billion and 2 billion.

Multiple Declarations

Dim a, b As Double

Two other types of multiple-declarationstatements are

Dim a As Double, b As IntegerDim c As Double = 2, b As Integer = 5

Parentheses

• Parentheses should be used liberally innumeric expressions.

• In the absence of parentheses, theoperations are carried out in the followingorder: ^, * and /, + and -.

Three Types of Errors

• Syntax error

• Run-time error

• Logic error

Some Types of Syntax Errors

• Misspellings lstBox.Itms.Add(3)

• Omissions lstBox.Items.Add(2 + )

• Incorrect punctuation Dim m; n As Integer

A Type of Run-time Error

• Overflow error

Dim numVar As Integer = 1000000numVar = numVar * numVar

A Logical Error

Dim average As DoubleDim m As Double = 5Dim n As Double = 10average = m + n / 2

Value of average will be 10. Should be 7.5.

3.4 Strings

• Variables and Strings

• Using Text Boxes for Input and Output

• Concatenation

• String Properties and Methods:

•Substring•IndexOf

•ToLower•Trim

•ToUpper•Length

Strings continued

• The Empty String

• Initial Value of a String

• Option Strict

• Internal Documentation

• Line-Continuation Character

String Literal

A string literal is a sequence of

characters surrounded by quotation marks.

Examples:"hello"

"123-45-6789""#ab cde?"

String Variable

A string variable is a name to which a

string value can be assigned.

Examples:

country

firstName

String Variable

• Declaration:Dim firstName As String

Variable nameData type

• Assignment:firstName = "Fred"

String Variable

You can declare a string variable and

assign it a value at the same time.

Dim firstName As String = "Fred"

Add Method

Let str be a string literal or variable. Then, lstBox.Items.Add(str)

displays the value of str in the list box.

String Variable

You can assign the value of one string

variable to another.

Dim strVar1 As String = "Hello"Dim strVar2 As String = "Goodbye"strVar2 = strVar1lstOutput.Items.Add(strVar2)

Output: Hello

Variables and StringsPrivate Sub btnDisplay_Click(...) Handles btnDisplay.Click Dim today As String today = "Monday" lstOutput.Items.Add("hello") lstOutput.Items.Add(today)End Sub

Output: hello Monday

Using Text Boxes for Input andOutput

• The contents of a text box is always a string

• Input example strVar = txtBox.Text

• Output example txtBox.Text = strVar

Data Conversion

• Because the contents of a text box isalways a string, sometimes you mustconvert the input or output.

dblVar = CDbl(txtBox.Text)

txtBox.Text = CStr(numVar)Converts a String to a Double

Converts a number to a string

Concatenation

Combining two strings to make a new string

quote1 = "We'll always "quote2 = "have Paris."quote = quote1 & quote2txtOutput.Text = quote & " - Humphrey Bogart"

DisplaysWe'll always have Paris. - Humphrey Bogart

Appending

• To append str to the string variable varvar = var & str

• Or as a shortcutvar &= str

Appending ExampleDim var As String = "Good"var &= "bye"txtBox.Text = var

OUTPUT: Goodbye

String Properties and Methods

"Visual".Length is 6.

"Visual".ToUpper is VISUAL.

"123 Hike".Length is 8.

"123 Hike".ToLower is 123 hike.

"a" & " bcd ".Trim & "efg" is abcdefg.

Positions in a StringPositions of characters in a string are numbered

0, 1, 2, ….

Consider the string “Visual Basic”.

Position 0: V

Position 1: i

Position 7: B

Substring “al” begins at position 4

Substring MethodLet str be a string.str.Substring(m, n) is the substring of length

n, beginning at position m in str.

“Visual Basic”.Substring(2, 3) is “sua”

“Visual Basic”.Substring(0, 1) is “V”

IndexOf MethodLet str1 and str2 be strings. str1.IndexOf(str2)

is the position of the first occurrence of str2 in str1.

(Note: Has value -1 if str2 is not a substring of str1.)

"Visual Basic".IndexOf("is") is 1.

"Visual Basic".IndexOf("si") is 9.

"Visual Basic".IndexOf("ab") is -1.

The Empty String• The string "", which contains no characters, is

called the empty string or the zero-lengthstring.

• The statement lstBox.Items.Add("") skips aline in the list box.

• The contents of a text box can be cleared witheither the statement

txtBox.Clear()• or the statement txtBox.Text = ""

Initial Value of a String

• By default the initial value is Nothing

• Strings can be given a different initialvalue as follows:

Dim today As String = "Monday"

Option Strict

• Visual Basic allows numeric variables tobe assigned strings and vice versa, apoor programming practice.

• To turn this feature off, put the followingstatement at the very top of the codewindow

Option Strict On

Option Strict On for All Programs

• Select Options from the Tools menu

• In left pane, expand Projects andSolution

• Select VB Defaults

• Set Option Strict to On

With Option Strict OnDim dblVar As Double, intVar As IntegerDim strVar As String

Not Valid: Replace with:intVar = dblVar intVar = CInt(dblVar)dblVar = strVar dblVar = CDbl(strVar)strVar = intVar strVar = CStr(intVar)

CommentsPrivate Sub btnCompute_Click (...) Handles btnCompute.Click 'Calculate the balance in an account Dim rate As Double 'Annual rate of interest Dim curBalance As Double 'Current balance

Internal Documentation

1. Other people can easily understand theprogram.

2. You can understand the program whenyou read it later.

3. Long programs are easier to readbecause the purposes of individualpieces can be determined at a glance.

Automatic Colorization

Comments – green

String literals – maroon

Keywords – blue

Note: Keywords are words such as Sub,

Handles, Private, With, and End that have

special meaning in Visual Basic. They

cannot be used as variable names.

Line-Continuation Character

• A long line of code can be continued onanother line by using an underscore (_)preceded by a space

msg = "I'm going to make " & _ "him an offer he can't refuse."

3.5 Input and Output

• Formatting Output with Format Functions

• Formatting Output with Zones

• Reading Data from Files

• Getting Input from an Input Dialog Box

• Using a Message Dialog Box for Output

• Using a Masked Text Box for Input

Formatting Output with FormatFunctions

18%FormatPercent(0.183, 0)

$12,345.63FormatCurrency(12345.628, 2)

12,345.6FormatNumber(12345.628, 1)

String ValueFunction

Formatting Output with Zones

• Use a fixed-width font such as Courier New

• Divide the characters into zones with aformat string.

Dim fmtStr As String = "{0, 15}{1, 10}{2, 8}"lstOutput.Items.Add(String.Format(fmtStr, _ data0, data1, data2))

Formatting Output with ZonesDim fmtStr As String = "{0, -15}{1, 10}{2, 8}"lstOutput.Items.Add(String.Format(fmtStr, _ data0, data1, data2))

Here, 15 was preceded by a minus sign. This

produces left justification in 0th zone. There will

be right justification in the other two zones.

Zone Formatting Symbols

FormatPercent(data, r):Pr

FormatCurrency(data, r):Cr

FormatNumber(data, r):Nr

Effect on zoneSymbols: N, C, and P

Dim fmtStr As String = "{0,15:N1}{1,10:C2}{2,8:P0}"

Reading Data from Files

• Data can be stored in files and accessedwith a StreamReader object.

• We assume that the files are text files(that is, have extension .TXT) and haveone piece of data per line.

Sample File: PAYROLL.TXT

Mike Jones

John Smith

Hourly wage

Number of hours worked

Steps to Use StreamReaderExecute a statement of the form

Dim readerVar As IO.StreamReader = _ IO.File.OpenText(filespec)

or the pair of statements

Dim readerVar As IO.StreamReader readerVar = IO.File.OpenText(filespec)

Steps to Use StreamReaderRead items of data in order, one at a time,from the file with the ReadLine method.

strVar = readerVar.ReadLine

After the desired items have been read fromthe file, terminate the communications link

readerVar.Close()

Example using StreamReaderDim name As StringDim wage, hours As DoubleDim sr As IO.StreamReader = _ IO.File.OpenText("PAYROLL.TXT")name = sr.ReadLinewage = CDbl(sr.ReadLine)hours = CDbl(sr.ReadLine)lstBox.Items.Add(name & ": " & wage * hours)

OUTPUT: Mike Jones: 257.25

Comment on Example

Consider

lstBox.Items.Add(name & ": " & wage * hours)

The ampersand automatically converted

wage * hours into a string before concatenating.

We didn’t have to convert wage * hours with CStr.

Getting Input from an InputDialog Box

stringVar = InputBox(prompt, title)fileName = InputBox("Enter the name " _ & "of the file containing the " & _ "information.", "Name of File")

Prompt

Using a Message Dialog Boxfor OutputMsgBox(prompt, 0, title)

MsgBox("Nice try, but no cigar.", 0, _ "Consolation")

Prompt

Masked Text Box

Similar to an ordinary text box, but hasa Mask property that restricts what canbe typed into the masked text box.

Input Mask Dialog Box

A Mask setting is a sequence of characters,with 0, L, and & having special meanings.

0 Placeholder for a digit.

L Placeholder for a letter.

& Placeholder for a character or space.

Sample Masks

State abbreviation: LL

Phone number: 000-0000

Social Security Number: 000-00-0000

License plate: &&&&&&

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