Developing Microsoft .Net Applications for Windows (Visual Basic .Net) Class 5

1COMP3100E

Developing Microsoft .Net

Applications for Windows (Visual

Basic .Net)Class 5

COMP3100E

2COMP3100E

Objectives

Learn to write code to call a procedure & to create a procedure

Learn about Subroutines Learn about Functions Local and Global Variables Introduction to Arrays

3COMP3100E

Procedures

A block of Visual Basic statements enclosed by a declaration statement and an End statement. – All Visual Basic code is written within

procedures. A procedure is invoked from some

other place in the code. When it is finished executing, it

returns control to the code that invoked it; this code is known as the calling code.

The calling code is a statement, or an expression within a statement, that specifies the procedure by name and transfers control to it.

4COMP3100E

Types of Procedures

Visual Basic uses several types of procedures:

Sub procedures– perform actions but do not return a

value to the calling code. (Straight from Microsoft)

– Event-handling procedures are Sub procedures that execute in response to an event triggered by user action or by an occurrence in a program.

Function procedures– return a value to the calling code.

Property procedures – return and assign values of properties

on objects or modules.

5COMP3100E

Procedures and Structured Code

Every line of code in your application must be inside some procedure, such as Main, Calculate, or Button1_Click.

If you subdivide large procedures into smaller ones, your application is more readable.

Procedures are useful for – performing repeated or shared tasks

» such as frequently used calculations, text and control manipulation, and database operations.

– Being invoked from many different places in your code

» so you can use procedures as building blocks for your application.

Structuring your code with procedures gives you the following benefits: – Procedures allow you to break your programs

into discrete logical units. » You can debug separate units more easily than

you can an entire program without procedures. – You can use procedures developed for one

program in other programs, often with little or no modification.

6COMP3100E

SubroutineExample

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim X As Integer Dim Y As Integer

X = Val(TxtX.Text) Y = Val(TxtY.Text) Multiply(X, Y)End Sub

Sub Multiply (ByVal X As Integer, ByVal Y As Integer)

LblResult.Text = Str(X * Y)End Sub

7COMP3100E

The Header

Multiply (ByVal X As Integer, ByVal Y As Integer)

Procedure Name Argument List

– ByVal (By Value)» Indicates that the procedure cannot

replace or reassign the underlying variable element in the calling code.

» ByVal is the default in Visual Basic.

– ByRef (By Reference)» Indicates that the procedure can

modify the underlying variable in the calling code the same way the calling

– Name of Variable– Variable data type

8COMP3100E

Subroutine Example 2


Dim X As Integer

Dim Y As Integer

Dim Z As Integer

X = Val(TxtX.Text)

Y = Val(TxtY.Text)

Multiply(X, Y, Z)

LblResult.Text = Str(Z)End Sub

Sub Multiply(ByVal X As Integer, ByVal Y As Integer, ByRef Z As Integer)

Z = X * YEnd Sub

9COMP3100E

Another Subroutine

Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click

'Display the sum of two numbersDim num1, num2 As Double

lstResult.Items.Clear()

ExplainPurpose()

lstResult.Items.Add("")

num1 = 2

num2 = 3

lstResult.Items.Add("The sum of " & num1 & " and " _

& num2 & " is " & num1 + num2 & ".")

End Sub

Sub ExplainPurpose()

REM Explain the task performed by the program

lstResult.Items.Add("This program displays a sentence")

lstResult.Items.Add("identifying two numbers and their sum.")

End Sub

10COMP3100E

Another Subroutine #2

Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click

'Display the sum of two numbers lstResult.Items.Clear() ExplainPurpose() lstResult.Items.Add("") Sum(2, 3)End Sub

Sub Sum(ByVal num1 As Double, ByVal num2 As Double)

'Display numbers and their sumlstResult.Items.Add("The sum of " & num1 & " and " _ & num2 & " is " & (num1 + num2) & ".") End Sub

Sub ExplainPurpose()'Explain the task performed by the programlstResult.Items.Add("This program displays a

sentence")lstResult.Items.Add("identifying two numbers and

their sum.") End Sub

11COMP3100E

Example of Structure

Private Sub btnCompute_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCompute.Click

'This program requests two numbers and

'displays the two numbers and their sum.

Dim x As Double 'First number

Dim y As Double 'Second number

Dim t As Double 'Total

GetNumbers(x, y)

CalculateSum(x, y, t)

DisplayResult(x, y, t)End Sub

Sub GetNumbers(ByRef num1 As Double, ByRef num2 As Double)

'Retrieve the two numbers in the text boxes

num1 = CDbl(txtFirstNum.Text)

num2 = CDbl(txtSecondNum.Text)

End Sub

Sub CalculateSum(ByVal num1 As Double, ByVal num2 As Double, _

ByRef total As Double)

'Add the values of num1 and num2

total = num1 + num2End Sub

Sub DisplayResult(ByVal num1 As Double, ByVal num2 As Double, _

ByVal total As Double)

txtResult.Text = "The sum of " & num1 & " and " & num2 _

& " is " & total & "."End Sub

12COMP3100E

Option Explicit

Visual Basic .NET generally allows implicit conversions of any data type to any other data type. Data loss can occur when the value of one data type is converted to a data type with less precision or smaller capacity, however, a run-time error message will occur if data will be lost in such a conversion. – Option Strict ensures compile-time

notification of these types of conversions so they may be avoided.

In addition to the conditions described above, Option Strict generates an error for: – Any undeclared variable since it is

implied that Option Strict also means Option Explicit.

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Option Strict ON

Option Strict On

Public Class Form1 Inherits System.Windows.Forms.Form

Private Sub btnConvert_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnConvert.Click

Dim FahrenheitTemp, CelsiusTemp As Double

FahrenheitTemp = CDbl(txtTempF.Text) CelsiusTemp = FtoC(FahrenheitTemp) txtTempC.Text = CStr(CelsiusTemp)Note: The above four lines can be replaced with the

single line'txtTempC.Text = CStr(FtoC(CDbl(txtTempF.Text)))End Sub

Function FtoC(ByVal t As Double) As Double 'Convert Fahrenheit temperature to Celsius Return (5 / 9) * (t - 32)End Function

End Class

14COMP3100E

Local Variables

Private Sub btnDisplay_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDisplay.Click

'Demonstrate the local nature of variables

Dim x As Double = 2

lstResults.Items.Clear()

lstResults.Items.Add(x)

Trivial()


Trivial()


End Sub

Sub Trivial()

'Do something trivial

Dim x As Double


x = 3


End Sub

15COMP3100E

Global Variables

Dim num1, num2 As Double 'Class-level variables


'Display the sum of two numbers

num1 = 2

num2 = 3

lstResults.Items.Clear()

AddAndIncrement()

lstResults.Items.Add("")

lstResults.Items.Add("num1 = " & num1)

lstResults.Items.Add("num2 = " & num2)

End Sub

Sub AddAndIncrement()

'Display numbers and their sum

lstResults.Items.Add("The sum of " & num1 & " and " & _

num2 & " is " & (num1 + num2) & ".")

num1 += 1 'Add 1 to the value of num1

num2 += 1 'Add 1 to the value of num2

End Sub

16COMP3100E

Intializing Values

Option Strict On

Public Class Form1 Inherits System.Windows.Forms.Form

+Windows Form Designer Generated Code

Dim pi As Double = 3.14159


'Display the area of a circle of radius 5 txtArea.Text = "The area of a circle of radius 5 is " & (pi * 5

* 5) End Sub

End Class

17COMP3100E

Function

Private Sub Button1_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles Button1.Click

Dim X As Integer Dim Y As Integer Dim Z As Integer

X = Val(TxtX.Text) Y = Val(TxtY.Text)

LblResult.Text = Multiply(X, Y)End Sub

Sub Multiply(ByVal X As Integer, ByVal Y As Integer, _ ByRef Z As Integer) Z = X * YEnd Sub

Function multiply(ByVal x As Integer, ByVal y As Integer) As Integer Return (x * y)End Function

18COMP3100E

Function Calls

Private Sub btnConvert_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnConvert.Click

Dim FahrenheitTemp, CelsiusTemp As Double

FahrenheitTemp = CDbl(txtTempF.Text)

CelsiusTemp = FtoC(FahrenheitTemp)

txtTempC.Text = CStr(CelsiusTemp)

Note: The above four lines can be replaced with the single line

'txtTempC.Text = CStr(FtoC(CDbl(txtTempF.Text)))

End Sub

Function FtoC(ByVal t As Double) As Double

'Convert Fahrenheit temperature to Celsius

Return (5 / 9) * (t - 32)

End Function

19COMP3100E

Function Example #2

Private Sub btnDetermine_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDetermine.Click

'Determine a person's first name

Dim name As String

name = txtFullName.Text

txtFirstname.Text = FirstName(name)

End Sub

Function FirstName(ByVal name As String) As String

'Extract the first name from a full name

Dim firstSpace As Integer

firstSpace = name.IndexOf(" ")

Return name.Substring(0, firstSpace)

End Function

20COMP3100E

Function Example #3

Private Sub btnCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalculate.Click

'Calculate the length of the hypotenuse of a right

'triangle

Dim a, b As Double

a = CDbl(txtSideOne.Text)

b = CDbl(txtSideTwo.Text)

txtHyp.Text = CStr(Hypotenuse(a, b))

End Sub

Function Hypotenuse(ByVal a As Double, _

ByVal b As Double) As Double

'Calculate the hypotenuse of a right triangle

'having sides of lengths a and b

Return Math.Sqrt(a ^ 2 + b ^ 2)

End Function

21COMP3100E

Business Example


'Find the future value of a bank deposit

Dim p As Double 'principal, the amount deposited Dim r As Double 'annual rate of interest Dim c As Double 'number of times interest is 'compounded per year Dim n As Double 'number of years InputData(p, r, c, n) DisplayBalance(p, r, c, n)End Sub

Sub InputData(ByRef p As Double, ByRef r As Double, _

ByRef c As Double, ByRef n As Double)

'Get the four values from the text boxes p = CDbl(txtAmount.Text) r = CDbl(txtRate.Text) c = CDbl(txtNumComp.Text) n = CDbl(txtNumYrs.Text)End Sub

22COMP3100E

Business Example Continued

Sub DisplayBalance(ByVal p As Double, _ ByVal r As Double, _ ByVal c As Double, _ ByVal n As Double)'Display the balance in a text box

Dim balance As Double balance = FutureValue(p, r, c, n) txtbalance.Text = FormatCurrency(balance)End Sub

Function FutureValue(ByVal p As Double, _ ByVal r As Double, _ ByVal c As Double, _ ByVal n As Double) As Double'Find the future value of a bank savings account'p principal, the amount deposited'r annual rate of interest'c number of times interest is compounded per year'n number of years Dim i As Double 'interest rate per period Dim m As Double 'total number of times interest 'is compounded i = r / c m = c * n Return p * ((1 + i) ^ m) End Function

23COMP3100E

What are arrays?

Arrays allow you to refer to a series of variables by the same name and to use a number, called an index or subscript, to tell them apart. – This helps you create shorter and simpler code in

many situations, because you can set up loops that deal efficiently with any number of elements by using the index number.

Every dimension of an array has a nonzero length. The elements of the array are contiguous along each dimension from subscript 0 through the highest subscript of that dimension. – Because Visual Basic allocates space for an array

element corresponding to each index number, you should avoid declaring any dimension of an array larger than necessary.

– Arrays do not have fixed size in Visual Basic. You can change the size of an array after you have created it. The ReDim statement assigns a completely new array object to the specified array variable. Therefore, ReDim can change the length of each dimension.

Simple Arrays contain values of only 1 data type

24COMP3100E

Creating Arrays

Dim monthNames(11) as string– monthNames(0) = "January"– monthNames(1) = "February"– monthNames(2) = "March"– monthNames(3) = "April"– monthNames(4) = "May"– monthNames(5) = "June"– monthNames(6) = "July"– monthNames(7) = "August"– monthNames(8) = "September"– monthNames(9) = "October“– monthNames(10) = “November”– monthNames(11) = “December”

25COMP3100E

Using Arrays

Dim monthNum As Integer

Rem Display month name

Picture1.Cls

monthNum =Val(InputBox ("Enter month number:"))

txtMonthName.Text = “Month name is “ & _ monthNames(monthNum)

26COMP3100E

Using Arrays (Your teacher)

Dim teamName(3) As String

Private Sub btnWhoWon_Click(ByVal sender As _ System.Object, ByVal e As _ System.EventArgs) _ Handles btnWhoWon.Click

Dim n As Integer n = CInt(txtNumber.Text) txtWinner.Text = teamName(n -1)End Sub

Private Sub Form1_Load(ByVal sender As _ System.Object, ByVal e As System.EventArgs) _ Handles MyBase.Load

'Place Super Bowl Winners into the array teamName(0) = "Packers" teamName(1) = "Packers" teamName(2) = "Jets" teamName(3) = "Chiefs"End Sub

27COMP3100E

Simple Swap

Private Sub btnAlphabetize_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAlphabetize.Click

'Alphabetize two words

Dim firstWord, secondWord, temp As String

firstWord = txtFirstWord.Text

secondWord = txtSecondWord.Text

If (firstWord > secondWord) Then 'Swap the two words

temp = firstWord

firstWord = secondWord

secondWord = temp

End If

txtResult.Text = firstWord & " before " & secondWord

End Sub

28COMP3100E

Using Array.Sort

Public Class Form1 Dim RandArray(0 To 499) As Long

'Initialize the Progress bar object and display num of elements

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

ProgressBar1.Minimum = 0 ProgressBar1.Maximum = UBound(RandArray) Label2.Text = UBound(RandArray) + 1End Sub

'Fill the array with random numbers and display in text box


Dim i As Integer For i = 0 To UBound(RandArray) RandArray(i) = Int(Rnd() * 1000000) TextBox1.Text = TextBox1.Text & RandArray(i) &

vbCrLf ProgressBar1.Value = i 'move progress bar Next iEnd Sub

29COMP3100E

Array.sort continued

'Sort the array using the Array.Sort method and display


Dim i As Integer TextBox1.Text = "" Array.Sort(RandArray) For i = 0 To UBound(RandArray) TextBox1.Text = TextBox1.Text & RandArray(i) &

vbCrLf ProgressBar1.Value = i 'move progress bar Next iEnd Sub

'Reverse the order of array elements using Array.Reverse


Dim i As Integer TextBox1.Text = "" Array.Reverse(RandArray) For i = 0 To UBound(RandArray) TextBox1.Text = TextBox1.Text & RandArray(i) &

vbCrLf ProgressBar1.Value = i 'move progress bar Next iEnd Sub End Class

30COMP3100E

Bubble Sort

Dim person() As String = _ {"Pebbles", "Barney", "Wilma", "Fred", "Dino"}

Private Sub Form1_Load(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyBase.Load

'Display unsorted list Dim i As Integer For i = 0 To 4 lstPeople.Items.Add(person(i)) Next iEnd Sub

Private Sub btnSort_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnSort.Click

‘Bubble sort names Dim passNum, i As Integer, temp As String Dim Done As Boolean passNum = 1 Do Done = True For i = 0 To 4 - passNum If (person(i) > person(i + 1)) Then Done = False temp = person(i) person(i) = person(i + 1) person(i + 1) = temp End If Next i passNum = passNum + 1 Loop While (Not Done) lstPeople.Items.Clear() For i = 0 To 4 lstPeople.Items.Add(person(i)) Next End Sub

31COMP3100E

Shell Sort

Dim part(50) As String

Dim numParts As Integer


'Read names of parts

numParts = 0 'Number of parts

Dim sr As IO.StreamReader = IO.File.OpenText("SHOEPART.TXT")

Do While (sr.Peek <> -1) And (numParts < part.GetUpperBound(0))

numParts += 1

part(numParts) = sr.ReadLine

Loop

sr.Close()

End Sub


'Sort and display parts of running shoe

SortData()

ShowData()

End Sub

32COMP3100E

Shell Sort

Sub SortData()'Shell sort shoe parts Dim gap As Integer, doneFlag As Boolean Dim index As Integer, temp As String

gap = CInt(numParts / 2) Do While (gap >= 1) Do done = True For index = 1 To numParts - gap If (part(index) > part(index + gap)) Then temp = part(index) part(index) = part(index + gap) part(index + gap) = temp done = False End If Next index Loop while (not done) gap = CInt(gap / 2) LoopEnd Sub

33COMP3100E

Fixed Arrays

Public Class Form1Dim Temperatures(0 To 6) As Single


End SubPrivate Sub Button1_Click(ByVal sender As

System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim Prompt, Title As String Dim i As Short Prompt = "Enter the day’s high temperature." For i = 0 To UBound(Temperatures) Title = "Day " & (i + 1) Temperatures(i) = InputBox(Prompt, Title) NextEnd Sub

34COMP3100E

Fixed Arrays Continued


Dim Result As String Dim i As Short Dim Total As Single = 0 Result = "High temperatures for the

week:" & vbCrLf & vbCrLf For i = 0 To UBound(Temperatures) Result = Result & "Day " & _

(i + 1) & vbTab & _ Temperatures(i) & vbCrLf Total = Total + Temperatures(i) Next Result = Result & vbCrLf & _ "Average temperature: " & _

Format(Total / 7, "0.0") TextBox1.Text = ResultEnd SubEnd Class

35COMP3100E

Dynamic Arrays

Public Class Form1 Dim Temperatures() As Single Dim Days As Integer


End SubPrivate Sub Button1_Click(ByVal sender As

System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim Prompt, Title As String Dim i As Short Prompt = "Enter the day’s high temperature." Days = InputBox("How many days?", "Create Array") If Days > 0 Then ReDim Temperatures(Days - 1) For i = 0 To UBound(Temperatures) Title = "Day " & (i + 1) Temperatures(i) = InputBox(Prompt, Title) NextEnd Sub

36COMP3100E

Dynamic Arrays Continued


Dim Result As String Dim i As Short Dim Total As Single = 0 Result = "High temperatures:" & _ vbCrLf & vbCrLf For i = 0 To UBound(Temperatures) Result = Result & "Day " & (i + 1) & vbTab & _ Temperatures(i) & vbCrLf Total = Total + Temperatures(i) Next Result = Result & vbCrLf & _ "Average temperature: " & _ Format(Total / Days, "0.0") TextBox1.Text = ResultEnd SubEnd Class

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Developing Microsoft .Net Applications for Windows (Visual Basic .Net) Class 5