这是一个PPT中利用VBS抽奖的代码，怎样才能实现已抽题目中抽了四次之后就变成白的重新开始四次抽奖

Private Num As Integer

Private Sub 开始_Click()

    停止.Enabled = True

    开始.Enabled = False

    结果框.Text = ""

    Dim a As Integer

    Randomize

    Do

        If 停止.Enabled = False Then

      州桥      结果框.Text = 抽取框.Text

            Num = Num + 1

            If Num <= 4 Then

                If 已抽题目.Text = "" Then

                    b = ""

                Else

                    b = " # "

                End If

                已抽题目.Text = 已抽题目.Text & b & 抽取框.Text

            Else

                Num = 1

                已抽题目.Text = 抽取框.Text

            End If

            

            Exit Do

        Else

            a = Fix(Rnd * 10 + 1)

           闷清 抽取框.Text = a

        End If

        

        DoEvents

    Loop

    开始.Enabled = True

End Sub

Private Sub 停止_Click()

    停止.Enabled = False

End Sub

Private Sub 打开抽取的题目_Click()

    ActivePresentation.SlideShowWindow.View.GotoSlide (Val(抽取框.Text + 1))

End Sub

' 说明：

' 册罩猛1、可能需要保存为启用宏的文档

' 2、去除了end命令，在调试状态需要手动点击代码编辑窗口的“重新设置”按钮结束程序

Dim a(1 To 100) As String

Dim i As Integer, x As Integer

Const n = 3 'n的值可根据实际需要赋予不同的变量

Private Sub Command1_Click()

Timer1.Enabled = True

End Sub

Private Sub Command2_Click()

Timer1.Enabled = False

End Sub

Private Sub Form_Load()

Randomize '游唤没初始化随机数生成器

a(1) = "富士康" '以此将n个人神纳的姓链晌名保存在数组a中

a(2) = "庞麦郎"

a(3) = "非主流"

For i = 1 To n

List1.AddItem a(i)

Next

Timer1.Enabled = False

End Sub

Private Sub Timer1_Timer()

x = Rnd() * n + 1 '产生一个[1，n]中的随机整数并存入变量x中

Label2.Caption = a(x) '在标签Label2中显示下标变量a(x)的值（第x个人的姓名）

End Sub

语言实现此程序。

以下是VB编程语言的实现示例：

'定义变量，存储每个奖项的人数

Dim firstPrize As Integer = 3

Dim secondPrize As Integer = 5

Dim thirdPrize As Integer = 12

Dim souvenirPrize As Integer = 10

'定义变量，存储抽奖结果

Dim firstPrizeList As New List(Of Integer)

Dim secondPrizeList As New List(Of Integer)

Dim thirdPrizeList As New List(Of Integer)

Dim souvenirPrizeList As New List(Of Integer)

'定义变量，存储编号滚动的起始编号

Dim currentNum As Integer = 1

'循环抽取各种奖项

For i As Integer = 1 To firstPrize

'抽取一等奖，并将编号添加到一等奖名单中

firstPrizeList.Add(currentNum)

currentNum += 1

Next

For i As Integer = 1 To secondPrize

'抽取二等奖，并将编号添加到二等奖名单中

secondPrizeList.Add(currentNum)

currentNum += 1

Next

For i As Integer = 1 To thirdPrize

'抽取三等奖，并将编洞派号添加到三等奖名单中

thirdPrizeList.Add(currentNum)

currentNum += 1

Next

For i As Integer = 1 To souvenirPrize

'抽取纪念奖，并将编纳档贺号添加到纪念奖名单中

souvenirPrizeList.Add(currentNum)

currentNum += 1

Next

'输出抽奖结果

Console.WriteLine("一等奖名单：" &String.Join(",", firstPrizeList))

Console.WriteLine("二等奖名单：" &String.Join("蠢凯,", secondPrizeList))

Console.WriteLine("三等奖名单：" &String.Join(",", thirdPrizeList))

Console.WriteLine("纪念奖名单：" &String.Join(",", souvenirPrizeList))

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