[VB教學]VB的程序控制

VB的程序控制

• If Statement
• Select Case
• For Next Loop/Exiting For Loop/Continue For
• Do Until Loop
• Do While Loop

If...Then...Else

If 條件1 [ Then ]
    若條件1為真,會執行此處的陳述式
[ ElseIf 條件2 [ Then ]
    若條件2為真,會執行此處的陳述式 ]
[ Else
    [ 不符以上條件才執行此處的陳述式 ] ]
End If

程式範例

        Dim score As Integer = 0
        Console.WriteLine("請輸入分數:")
        score = Console.ReadLine()
       
        If score >= 60 Then
            Console.WriteLine("及格")
        ElseIf score < 60 & score >= 40 Then
            Console.WriteLine("活當")
        Else
            Console.WriteLine("死當")
        End If

Select Case

Select [ Case ] 變數名稱

    [ Case 列舉或條件
        [ 符合,執行此處的陳述式 ] ]
    [ Case Else
        [ 以上都不符,執行此處的陳述式 ] ]
End Select
case可以使用的方法如下,只要逗點就可以把該case的條件一值加下去

   Case 1 To 4, 7 To 9, 11, 13, Is > maxNumber
   Case的資料型態在2010支援Boolean、Byte、Char、Date、Double、 Decimal、         Integer、Long、Object、SByte、Short、Single、String、UInteger、ULong 和 UShort


程式範例
    Dim MyInt As Integer = Nothing
        Console.WriteLine("Plz Enter an integer:")
        MyInt = Console.ReadLine()

        Select Case MyInt
            Case 0
                Console.WriteLine("Hello 0")
            Case 1 To 9
                Console.WriteLine("Hello 1~9")
            Case 10, 11, 12
                Console.WriteLine("Hello 10,11,12")
            Case Else
                Console.WriteLine("Hello Else")
        End Select

For...Next Statement
For 變數 [ As datatype ] = 開始數值 To 結束數值 [ Step 間隔 ]
    [ 陳述式 ]
    [ Continue For ]
    [ 陳述式 ]
    [ Exit For ]
    [ 陳述式 ]
Next [ 變數 ]
程式範例 
        Dim Int1 As Integer

        For Int1 = 1 To 20
            Console.WriteLine("it's " & Int1)
        Next
        Console.WriteLine()
        For Int1 = 1 To 20 Step 2  '執行1,3,5,7,9...,19
            Console.WriteLine("(step:2)it's " & Int1)
        Next
        Console.WriteLine()

        For Int1 = 20 To 1 Step -2
            If Int1 = 2 Then  '若Int1 = 2跳出整個ForLoop
                Exit For
            End If
            If Int1 = 5 Then  '若Int1 = 5跳過底下剩餘程式,直接進入下一次回圈
                Continue For
            End If
            Console.WriteLine("(step:-2)it's " & Int1)
        Next
Do ... Loop
Do { While | Until } 條件
    [ 陳述式]
    [ Exit Do ]==>若符合IF條件就可以離開該DO Loop
    [ 陳述式 ]
Loop
-or-
Do
    [ 第一次一定執行陳述式 ]
    [ Exit Do ]==>若符合IF條件就可以離開該DO Loop
    [ 陳述式 ]
Loop { While | Until } 條件
While:條件為真執行下一個Loop 
Until :條件為真跳出Loop 

程式範例     
    Dim check As Boolean = True
    Dim counter As Integer = 0
    Do
        Do While counter < 20
            counter += 1
            If counter = 10 Then
                check = False
                Exit Do
            End If
        Loop
    Loop Until check = False
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