求素数个数.frm

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VERSION 5.00
Begin VB.Form Form1 
   Caption         =   "例[8-13]求素数的个数"
   ClientHeight    =   1080
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   3870
   LinkTopic       =   "Form1"
   ScaleHeight     =   1080
   ScaleWidth      =   3870
   StartUpPosition =   3  '窗口缺省
   Begin VB.Label Label2 
      BorderStyle     =   1  'Fixed Single
      Height          =   435
      Left            =   2535
      TabIndex        =   1
      Top             =   360
      Width           =   1095
   End
   Begin VB.Label Label1 
      Caption         =   "500~1999之间的素数个数："
      Height          =   375
      Left            =   248
      TabIndex        =   0
      Top             =   413
      Width           =   2895
   End
End
Attribute VB_Name = "Form1"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Private Sub Form_Click()
  Dim i As Integer, num As Integer
  num = 0
  For i = 500 To 1999
    If (isprime(i) And (i Mod 100) \ 10 = 7) Then num = num + 1
  Next i
  Label2.Caption = Str(num)
End Sub
Private Function isprime(k As Integer) As Boolean
   '本函数isprime判断正整数k是否为素数，函数返回值为Boolean类型
  Dim i As Integer
  isprime = True              '先假设该数为素数，isprime赋值为True
  If (k <= 1) Then
    isprime = False
    Exit Function
  End If
  For i = 2 To k - 1
    If (k Mod i = 0) Then    '如果该数能被2~k-1之间的某一个数整除，
      isprime = False       '则该数不是一个素数，isprime赋值为False
      Exit Function
    End If
  Next i
End Function