求教VB问题

Private Function IsPrime(ByVal x As Integer) As Boolean
    Dim i As Integer
    For i = 2 To Sqr(x)
        If x Mod i = 0 Then
            IsPrime = False
            Exit Function
        End If
    Next
    IsPrime = True
End Function

------------------------------------------------

Private Sub cmdFind_Click()
 Dim j As Integer
 Dim n As Integer
  n = Val(txtInput.Text) - 1
  For j = 0 To 2
  While Not IsPrime(n)
      n = n - 1
    Wend
    lblResult(j).Caption = n
    n = n - 1
    Next
  -------------------------------------------------- 
 

    Open App.Path & "\out5.dat" For Output As #1
 Print #1, txtInput.Text, lblResult(0).Caption, lblResult(1).Caption, lblResult(2).Caption
    Close #1
End Sub

 

 

 

中间横线画出来的就是问题    我的问题就是  第二个n=n-1到底是为什么要写 我根本没看出来 写他的意义在哪

lblResult(j).Caption = n
这里已经将N给LABEL了   再继续下边的循环时 当然要再给他减一了  要不就重复是那一个数了