1 chapter 10 additional control structures and exceptions

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Chapter 10Additional Control Structures

and Exceptions

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Chapter 10 Topics

Select Case Multiway Branching Structure

Do-Loop While Statement for Looping For statement for Looping Bitwise Logical Operators Assignment operators Exception Handling using Try and Catch Defining Exception Classes

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10.1 Select Case Statement

Is a selection control structure for multiway branching(多重分支 ).

SYNTAXSelect Case (Test Expression) Case [expression1 to expression2] [Is comparison

operator expression] [expression], [expression]

Statements(s)... Case Else

Statement(s)End Select

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Select Case (digit) Case 1

Console.WriteLine( “digit is " & “1”) Case 2, 3

Console.WriteLine (“digit is " & “2 or 3”) Case 4

Console.WriteLine (“digit is " & “4”) Case Else

Console.WriteLine (“digit is " & “others”)

End Select

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Select Case Statement

The value of TestExpresssion (of Boolean, Byte, Char, Date, Double, Decimal, Integer, Long, Object, Short, Single, and String) determines which branch is executed

Case expressions can consist of a single expression, multiple expressions separated by commas, of the form Expression1 to Expression2 Is (comparison operator) expression

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Control in Select Case Statement

Control branches to the statement following the Case clause whose expression matches the TestExpression . Each statement in the clause is executed, and then control falls out of the Select Case Statement.

If no Case clause expression matches the TestExpression, control falls to the statement inside Case Else, if present. Otherwise, control falls out of the Select Case Statement

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Select Case (digit) Case 2, 3

Console.WriteLine (“digit is " & “2 or 3”) Case 1

Console.WriteLine( “digit is " & “1”) Case 4

Console.WriteLine (“digit is " & “4”) Case Else

Console.WriteLine (“digit is " & “others”)

End Select

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Select Case (grade) Case "A", "B"

MsgBox( “Good Work”) Case “C"

MsgBox( “Average Work”) Case “D“, “F”

MsgBox( “Poor Work”) Case Else

MsgBox( grade & “is not a valid grade”)End Select

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Select Case (grade) Case 80 to 100

MsgBox( “Good Work”) Case 70 to 79

MsgBox( “Average Work”) Case 0 to 69



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Select Case (grade) Case Is > 79

MsgBox( “Good Work”) Case Is >= 70

MsgBox( “Average Work”) Case Is >= 0



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Do While-Loop While Statement Syntax

Very similar to the While Statement.

Do While-Loop Statement

Do While (Expression)statement

Loop

Loop body can be a single statement or a block.

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'Count controlled repetitionsum = 0 'Initializecounter = 1Do While (counter <= 10) 'Condition sum = sum + counter counter += 1 'Incrementloop

Using Do While-Loop to implement a count-controlled loop

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Do-Loop While Statement Syntax

Is a looping control structure in which the loop condition is tested after executing the body of the loop.

Do-Loop While Statement

Dostatement

Loop While (Expression)

Loop body can be a single statement or a block.

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Do-Loop While Flowchart

When the expression is tested and found to be false, the loop is exited and control passes to the statement that follows the Do-Loop While statement.

Statement

Expression

DO

LOOP WHILE

False

True

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'Count controlled repetitionsum = 0 'Initializecounter = 1Do sum = sum + counter counter += 1 'Incrementloop While (counter <= 10) 'Condition

'Count controlled repetition

sum = 0 'Initializecounter = 1While (counter <= 10) sum = sum + counter counter += 1End While

Using Do-Loop While to implement a count-controlled loop

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Do-Loop vs. While

POSTTEST loop (exit-condition)

(後測離開條件 ) The loop condition is

tested after executing the loop body.

Loop body is always executed at least once.

PRETEST loop (entry-condition)

(前測進入條件 ) The loop condition is

tested before executing the loop body.

Loop body may not be executed at all.

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For Statement

For control-var = Init To End [ Step Incr ]

Statement

Next control-var

For Statement Syntax

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The For statement contains

an initial value for the control variable

an ending value for the control variable

an optional increment value for the control variable after each iteration of the loop body

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Example of Repetition

Dim num As Integer

For num = 1 To 3

Console.WriteLine("P" & num)

Next

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num

Dim num As Integer

For num = 1 To 3

Console.WriteLine ("Potato" & num)

Next

OUTPUT

?

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num

Dim num As Integer

For num = 1 To 3


Next

OUTPUT

1

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num

Dim num As Integer

For num = 1 To 3


Next

OUTPUT

1

Potato1

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num

Dim num As Integer

For num = 1 To 3


Next

OUTPUT

1

Potato1

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num

Dim num As Integer

For num = 1 To 3


Next

OUTPUT

2

Potato1

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num

Dim num As Integer

For num = 1 To 3


Next

OUTPUT

2

Potato1Potato2

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num

Dim num As Integer

For num = 1 To 3


Next

OUTPUT

2

Potato1Potato2

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num

Dim num As Integer

For num = 1 To 3


Next

OUTPUT

3

Potato1Potato2

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num

Dim num As Integer

For num = 1 To 3


Next

OUTPUT

3

Potato1Potato2Potato3

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num

Dim num As Integer

For num = 1 To 3


Next

OUTPUT

3


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num

Dim num As Integer

For num = 1 To 3


Next

OUTPUT

4


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num

Dim num As Integer

For num = 1 To 3


Next

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When the loop control variable (num) obtains a value greater than the ending value in the for, the loop is said to be “satisfied” and control passes to the statement following the for structure

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The output was:

Potato1

Potato2

Potato3

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What output from this loop?

Dim count As Integer

For count = 1 To 0

Console.WriteLine ("*")

Next

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No output from the for loop! Why?

The initial value of the loop control variable is greater than the ending value.

This means the loop is already satisfied. Control passes to the statement past the

end of the for loop

OUTPUT

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' Calculating compound interestDim year As IntegerDim amount As DoubleDim principle As Double = 1000.0Dim rate As Double = 0.07Console.WriteLine ("Year Amount")For year = 1 to 10 amount = principle * Math.Pow(1.0 + rate, year) Console.WriteLine(year & " " & amount)Next

Another count-controlled loop

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VB .NET Has Combined Assignment Operators

Dim i As Integer

Write a statement to add 5 to i.

i = i + 5

OR,

i += 5

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VB .NET Has Combined Assignment Operators

Dim pivotPoint As Integer

pivotPoint = pivotPoint * (n+3)

OR,

pivotPoint *= n+3

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Write a statement to subtract 10 from weight

Dim weight As Integer

weight = weight - 10

OR,

weight -= 10

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Write a statement to divide money by 5.0

Dim money As Double

money = money / 5.0

OR,

money /= 5.0;

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Write a statement to double profits

Dim profits As Double

profits = profits * 2.0

OR,

profits *= 2.0

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Write a statement to raise cost 15%

Dim cost As Double

OR,

cost = 1.15 * cost;

OR,

cost *= 1.15 ;

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Precedence (highest to lowest)Operator Associativity ( ) Left to right

^ Left to right- (negation) Left to right

* / Left to right \ (Integer division) Left to right Mod Left to right + - Left to right& (String concatenation) Left to right = Left to right <> Left to right <,> Left to right > = Left to right< = Left to right= += -= *= /= Right to left

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Case Study: Rainfall

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Imports System.IOModule Module1 Class DataSetException : Inherits SystemException Public Sub New(ByVal message As String) MyBase.New(message) End Sub End Class

Public Sub processOneSite(ByVal inFile As StreamReader, _ ByVal outFile As StreamWriter, _ ByVal dataSetName As String)

Dim count As Integer ' Loop control variable Dim amount As Double ' Rain for one month Dim sum As Double = 0.0 ' Sums annual rainfall Dim dataLine As String ' Input from inFile Dim currentValue As String ' String for numeric Dim index As Integer

Rainfall program

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Try dataLine = inFile.ReadLine() For count = 1 To 12 index = dataLine.IndexOf(" ") If (index > 0) Then currentValue = dataLine.Substring(0, index) dataLine = dataLine.Substring(Math.Min(index + 1, _ dataLine.Length()), _ dataLine.Length()) Else currentValue = dataLine End If amount = Double.Parse(currentValue) If (amount < 0.0) Then Throw New DataSetException("Negative in ") Else sum = sum + amount End If Next outFile.WriteLine("Average for " & dataSetName & _ " is " & sum / 12.0)

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Catch except As IOException outFile.WriteLine("IOException with site " & _

dataSetName) Catch except As FormatException outFile.WriteLine("FormatException in site " & _

dataSetName) Catch except As DataSetException outFile.WriteLine(except.ToString & dataSetName)

End Try

End Sub End Module

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Sub Main() Dim dataSetName As String ' Reporting station name Dim inFile As StreamReader ' Data file Dim outFile As StreamWriter ' Output file inFile = File.OpenText("rainData.dat") outFile = File.CreateText("outfile.dat")

' Get name of reporting station dataSetName = inFile.ReadLine

' Processing loop Do processOneSite(inFile, outFile, dataSetName) dataSetName = inFile.ReadLine() Loop While (inFile.Peek <> -1) inFile.Close() outFile.Close() Console.Write("press enter to quit") Console.Read() End Sub

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Exercises

Chapter 9 Programming problems: 1

Chapter 10 Exam preparation exercises:

– 5, 10,15– 11 ( For i=5 To 2 Step -1 )– 12 ( For row = 1 To 8 , 所有 10改為 8)

Programming warm-up exercises: – 1,5,7,9

Due Date: 12/15 ( 三 ) 請寫在 A4報表紙上，勿使用電腦列印

1 chapter 10 additional control structures and exceptions

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