下列程序计算Sn的值。Sn=a+aa+aaa+…a,其中最后一项为n个。 例如:a=5,n=4时,则Sn=5+55+555+5555。请在空白处填入适当的内容,将程序补充完整。 Private Sub Command1_Click( ) Dim a As Integer, n As Integer, Cout As Integer Dim Sn As Long, Tn As Long Cout = 1 Sn =0 Tn =0 a = InputBox('请输入a的值:' ) 【 】 Do Tn =Tn * 10 + a Sn = Sn + Tn Cout = Cout + 1 【 】 Debug. Print a, n, Sn End Sub