'约束用户输入的信息:只能为正整数(放在Text_Change中)
Public Sub checkinput(obj As TextBox)
   Dim i As Integer
   If Left(obj.Text, 1) = "0" Then
      obj.Text = ""
      MsgBox "仅能输入正整数!", 0, "注意"
      Exit Sub
   End If
   For i = 1 To Len(obj.Text)
       If Asc(Mid(obj.Text, i)) > 57 Or Asc(Mid(obj.Text, i)) < 48 Then
             obj.Text = ""
             MsgBox "仅能输入正整数!", 0, "注意"
             Exit Sub
       End If
    Next
End Sub