第二套 试题三( 21 分) 修改 VB 程序,使其具有下列功能:程序启动运行在文本框上显示 20 个 [10 , 99] 的随机整数。单击“素数个数”按钮,在标签 3 上显示出素数数列及标签 4 上显示素数个数。单击“平均数”按钮,在标签 4 上显示出此数列的平均数。运行效果如图 5 、图 6 所示。 Dim a%(1 To 20), k% Private Sub Form_Load() Randomize For i = 1 To 20 a(i) = + 10 '(1) Text1.Text = Text1.Text & a(i) & " " Next i End Sub Private Sub Command1_Click() Dim x%, f% For i = 1 To 20 f = 0 For j = 2 To a(i) - 1 If = 0 Then '(2) f = 1: Exit For End If Next j If f = 0 Then k = '(3) a(k) = a(i) If k = 1 Then Label3.Caption = a(k) Else Label3.Caption = '(4) End If End If Next i Label4.Caption = ' (5) End Sub Private Sub Command2_Click() Dim s% Dim pj! For i = 1 To k s = '(6) Next i pj = s / k Label4.Caption = Int(pj ) / 10 ' (7) End Sub