1. Controlling Program Flow with Looping Structures
Chapter 6
Controlling Program Flow with Looping Structures

2. 6.1 Looping -Applications often need to perform repetitive tasks.
-They use the same set of statements until a condition is met
-Repeating a set of statements is called looping or iteration

3. 6.2 The Do…Loop Statement
-The Do…Loop executes the statements at least once before it checks condition. If the condition is true it loops again until the condition is false.
-Format: Do
statements
Loop While condition
-Example:
Dim intNumber As Integer = 0
intNumber = intNumber + 2
Loop While intNumber < 10
-How many times did the above loop execute???

4. 6.2 Continued
-The Do While… Loop (Checks condition before it ever executes)
-Format:
Do While condition
statements
Loop
-How many times does a Do While … Loop have to execute???

5. 6.3 Infinite Loops
-A condition of a loop is used to tell a loop to stop. If that condition never becomes false the loop will continue forever. This is called an infinite loop.
-Example:
Dim intNumber As Integer = -1
Do While intNumber < 0
intNumber = intNumber -1
Loop
-While will this cause an infinite loop???
-To stop a program stuck in an infinite loop. Just click on the x in the top left hand corner of the title bar. Then choose end now when the dialog box appears.

6. Ch 6 – Review 1 -New Project -New form -Add 2 labels
(lblPromt, lblResult)
-Add 1 textbox
(txtInteger)
-Add 1 button
(btnTest)
-Add text change Event
-Add btnTest Click event.
Dim intTestNum As Integer = Val(Me.txtInteger.Text)
Dim intDivisor As Integer = 1
If intTestNum <= 1 Then
Me.lblResult.Text = "Not a prime number."
Else Do
intDivisor = intDivisor + 1
Loop While intTestNum Mod intDivisor <> 0
If intDivisor = intTestNum Then
Me.lblResult.Text = "Prime number."
End If

7. 6.4 Using an Input Box
-It’s a predefined dialog box that has a prompt, a text box, and OK and CANCEL buttons.
-Used to get input from the user
-Format:
variable = InputBox(prompt, title)
Example 1:
Dim strName as String
strName = InputBox (“Enter your full name:”, “Name”)
Example 2:
Dim intTestGrade as Integer
intTestGrade = Val(InputBox(“Enter the test grade”, “Grade”) )

8. 6.5 Accumulator Variables
-Accumulator is a variable storing a number that’s incremented by a changing value. Similar to counter variable from last chapter.
-Format:
accumulator = accumulator + value
-Example:
Dim intTestSum, intNewTest, intNumberofTests As Integer
Dim sngAverage as Single Do
intNewTest = Val(InputBox(“Enter test grade”, “Grade”))
intTestSum = intTestSum + intNewTest
Loop While intNewTest <> -1
sngAverage = intTestSum / intNumberofTests

9. 6.6 Using Flags
-Flags, or sentinels are conditions used to signify that a loop should stop executing
-Example:
Dim intFlag As Integer = -1
Dim intTestGrade, intTotal As Integer Do
intTestGrade = Val (InputBox(“Enter test grade or (-1) to quit.”))
if intTestGrade <> intFlag Then
intTotal = intTotal + intTestGrade
End If
Loop While intTestGrade <> intFlag

10. Ch 6 – Review 2 -New Project -New Form -Add 2 buttons
(btnEnterScores, btnAverageScore)
-Add 5 labels
(lblInstructions, lblScoresMessage,
lblNumberofScores, lblAverageMessage,
lblAverage)
-Add code from handout to each click event.

11. 6.7 The For … Next Statement
-A looping structure that executes a set of statements a fixed number of times
-Format:
For counter = start To end
statements
Next counter
-Example 1:
Dim intNumber As Integer
For intNumber = 1 to 10 Step 1
Messagebox.show(intNumber)
Next intNumber
-Example 2:
Dim intNumber As Integer
For intNumber = 10 to 1 Step -2
Messagebox.show(intNumber)
Next intNumber

12. Ch 6 – Review 4 -New Project -New Form -Add 1 text box (txtNumber)
-Add 1 button
(btnComputeFactorial)
-Add 3 labels
(lblPrompt, lblFactorial,
lblFactorialMessage)
-Add code to Click Event
-Add TextChange Event
Dim intNumber As Integer
Dim lngFactorial As Long = 1
Dim intCount As Integer
intNumber = Val(Me.txtNumber.Text)
For intCount = 1 To intNumber
lngFactorial = lngFactorial * intCount
Next intCount
Me.lblFactorialMessage.Text = "Factorial is:"
Me.lblFactorial.Text = lngFactorial

13. 6.8 The String Class What values get stored in the 3 variables???
-The String data type is a class
-Classes include properties and methods
-Properties:
Chars(index) -> returns the character at the specific location
Length -> returns the number of characters in the string
-Example 1:
Dim strName As String = “Ben Franklin”
Dim intLength As Integer
Dim chrPosition1, chrPosition2 As Char
intLength = strName.Length
chrPosition1 = strName.Chars(6)
chrPosition2 = strName.Chars(10)
What values get stored in the 3 variables???

14. 6.8 Continued -Methods ToUpper -> converts string to upper case
ToLower -> converts string to lower case
Trim -> removes spaces from beginning and end of String
TrimEnd -> removes spaces from end of String
TrimStart -> removes spaces from beginning of String
PadLeft(length, char) -> Adds certain number of characters to beginning of String
PadRight(length, char) -> Adds certain number of characters to end of String

15. 6.8 Continued -Examples: Dim strSeason As String = “SummerTime”
Dim strNewString As String
strNewString = strSeason.ToUpper
strNewString = strSeason.ToLower
strSeason = “ SummerTime “
strNewString = strSeason.Trim
strNewString = strSeason.TrimEnd
strNewString = strSeason.TrimStart
strSeason = “SummerTime”
strNewString = strSeason.PadLeft(15, “x”)
strNewString = strSeason.PadRight(13, “x”)
“SUMMERTIME”
“summertime”
“SummerTime”
“ SummerTime”
“SummerTime “
“xxxxxSummerTime”
“SummerTimexxx”

16. 6.8 Continued -More Methods -Substring (start position, # of char)
-returns a portion of the string
-Remove (start position, # of char)
-deletes a portion of the string
-Replace (old part, new part)
-replaces every old part with the new part
-Insert (start position, new part)
-inserts the new part into the string at the specified location
-IndexOf (search part)
-returns the position of the first occurrence of the search

17. 6.8 Continued -More Examples: Dim strSeason As String = “SummerTime”
Dim strNewString As String
Dim intPos As Integer
strNewString = strSeason.Substring(6,4)
strNewString = strSeason.Remove(0,6)
strNewString = strSeason.Replace(“Time”, “ is fun!!”)
strNewString = strSeason.Insert(6, “ is a fun ”)
intPos = strSeason.IndexOf(“mer”)
“Time”
“Time”
“Summer is fun!!”
“Summer is a fun Time” 3

18. Ch 6 – Review 6 -New Project -New Form -Add 1 Button (btnCountLetter)
-Add 2 TextBoxes
(txtText, txtSearch)
-Add 4 Labels
(lblTextPrompt,
lblSearchPrompt,
lblMessage, lblAnswer)
-Add both Text Change Events
-Add code to Click Event
Dim intChar As Integer = 0
Dim strText As String = Me.txtText.Text
Dim strSearchText As String = Me.txtSearch.Text
strText = strText.ToLower
strSearchText = strSearchText.ToLower
Dim intTextLength As Integer = strText.Length
Dim intCharacter As Integer
For intCharacter = 0 To intTextLength - 1
If strText.Chars(intCharacter) = strSearchText Then
intChar = intChar + 1
End If
Next
Me.lblMessage.Text = "Number of times letter occurs:"
Me.lblAnswer.Text = intChar

19. Ch 6 – Review 7 -New Project -New Form -Add 1 Button (btnDisplayData)
-Add 1 TextBox
(txtWord)
-Add 7 Labels
(lblPrompt, lblFirstLetter,
lblFirst, lblMiddleLetter,
lblMiddle, lblLastLetter,
lblLast)
-Add Text Changed Event
-Add code to Click Event
Dim strText As String = Me.txtWord.Text
Dim intLength As Integer = strText.Length
Dim chrFirst As Char = strText.Chars(0)
Dim chrMiddle As Char = strText.Chars(intLength \ 2)
Dim chrLast As Char = strText.Chars(intLength - 1)
Me.lblFirst.Text = chrFirst
Me.lblMiddle.Text = chrMiddle
Me.lblLast.Text = chrLast

20. Ch 6 – Review 8 -New Project -New Form -Add 1 Button (btnFindString)
-Add 2 TextBoxes
(txtText, txtSearch)
-Add 4 Labels
(lbltextPrompt,
lblSearchPrompt,
lblPositionMessage,
lblAnswer)
-Add 2 text changed Events
-Add code to Click Event
Dim strText As String = Me.txtText.Text
Dim strSearchText As String = Me.txtSearch.Text
Dim intPos As Integer = strText.IndexOf(strSearchText)
If intPos = -1 Then 'not found
Me.lblPositionMessage.Text = "Search text not found"
Else
Me.lblPositionMessage.Text = "Position of search text:"
Me.lblAnswer.Text = intPos
End If

21. 6.9 String Concatenation
-2 or more strings can be joined together in a process called concatenation
-The (&) symbol can be used to join multiple strings
-Example:
Dim strSeason As String = “SummerTime”
Dim strMessage As String = “ is a fun time!”
Dim strNewString As String
strNewString = strSeason & strMessage “SummerTime is a fun time!”

22. 6.9 Continued -Space(# of spaces) can be used to enter spaces Example:
me.lblMessage.text = “10” & space(10) & “spaces”
-vbTab Used to tab to the next field (each field has 8 characters)
me.lblMessage.text = “Mr.” & vbTab & “Newton”
-vbCrLf Used to enter a new line
Example;
me.lblMessage.text = “Mr.” & vbCrLf & “Newton”

23. Ch 6 – Review 9 -New Project -New Form -Add 1 Button (btnStart)
-Add 1 Label
(lblName)
-Add code to click event
Dim strFirstName As String
Dim strLastName As String
strFirstName = InputBox("Enter your first name: ", "First Name")
strLastName = InputBox("Enter your last name: ", "Last Name")
Dim strFullName As String = strFirstName & Space(1) & strLastName
Me.lblName.Text = strFullName

24. 6.10 The Char Structure -The Char data type is a structure.
-A structure is a simple form of a class
-Properties
ToLower(character) -> Changes character to lower case
ToUpper(character) -> Changes character to upper case
-Example:
Dim chrLetter As Char
chrLetter = Char.ToUpper(“b”) “B”
chrLetter = Char.ToLower(“E”) “e”

25. 6.11 Unicode
-Every letter/symbol of every language has a unique 16-bit binary code called UNICODE
-VB has 2 built in functions:
AscW (char) returns the integer Unicode value
ChrW (integer) returns the corresponding character
-See values on table to use functions.

26. Ch 6 – Review 10 -New Project -Add form -Add 1 button (btnStart)
-Add 1 label
(lblCode)
-Add code to click event
Dim intNumber As Integer
Dim chrUpperLetter As Char
Dim chrLowerLetter As Char
Dim intCode As Integer
For intNumber = 1 To 6
chrUpperLetter = InputBox("Enter an uppercase letter")
chrLowerLetter = Char.ToLower(chrUpperLetter)
intCode = AscW(chrLowerLetter)
Me.lblCode.Text = Me.lblCode.Text & intCode
Next intNumber

27. 6.12 Comparing Strings -Often a program will need to compare strings
-Relational operators can be used, but sometimes produces unexpected results
-Much better to use the Compare method
-Compare Method
Format:
Compare (string1, string2, Case-sensitive)
-False = case sensitive, true = not case sensitive
-if string1 is first it’s a negative number, if string2 is first it’s a positive number, if they’re the same its 0

28. 6.12 Continued Example: Select String.Compare(“Chris”, “Bob”, True)
Case 0
lblMessage.Text = “The Same”
Case Is < 0
lblMessage.Text = “Alphabetically before”
Case Is > 0
lblMessage.Text = “Alphabetically after”
End Select

29. Ch 6 – Review 11 -New Project -New Form -Add 2 textboxes
(txtFirst, txtSecond)
-Add 1 button
(btnCompareWords)
-Add 3 labels
(lblPrompt1, lblPrompt2, lblAnswer)
-Add code to Click Event
-Add 2 Text Change Events
Dim strWord1, strWord2 As String
strWord1 = Me.txtFirst.Text
strWord2 = Me.txtSecond.Text
Select Case String.Compare(strWord1, strWord2, True)
Case 0
Me.lblAnswer.Text = strWord1 & " is the same as " & strWord2
Case Is < 0
Me.lblAnswer.Text = strWord1 & " comes before " & strWord2
Case Is > 0
Me.lblAnswer.Text = strWord1 & " comes after " & strWord2
End Select

30. 6.13 The Like Operator