【正确答案】[解析] 控件在运行时是否可用由Enabled属性设置。当Enabled为True时，控件在运行时可用，当Enable为False时，控件在运行时不可用(灰色)；单击命令按钮触发其Click事件，其标题由Caption属性设置；Str$函数将数字转换为字符串。
解题步骤：
第一步：建立界面并设置控件属性。程序中用到的控件及其属性见表9-3。
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Option Explicit
Private Sub COMEXIT_Click()
End
End Sub
Private Sub COMSTART_Click()
Dim A As Integer, N As Integer, J As Integer, Sum As Single
A= 8: N= 4
For J = 1 To N
Sum = Sum + Item(A, J)
Next J
Print "Sum="; Sum
Open App. Path& "/" & "sjt5.dat" For Output As #1
Print #1, Sum
Close #1
'?.Caption = "完成"
'COMSTART.? = False
End Sub
Function Item(A, k)
Dim P As String, Q As String, S As Single
Dim i As Integer, H As Single
p = ""
For i = 1 To k
Q$ = Str$ (A)
p$ = p$ + Q$
Next i
'? = Val(P$)
'H = ? + S
Item = H
End Function
参考代码：
Option Explicit
Private Sub COMEXIT_Click()
End
End Sub
Private Sub COMSTART_Click()
Dim A As Integer, N As Integer, J As Integer, Sum As Single
A= 8: N = 4
For J = 1 To N
Sum = Sum + Item(A, J)
Next J
Print "Sum="; Sum
Open App. Path & "/" & "sjt5.dat" For Output As #1
Print #1, Sum
Close #1
COMSTART.Caption = "完成"
COMSTART.Enabled = False
End Sub
Function Item(A, k)
Dim P As String, Q As String, S As Single
Dim i As Integer, H As Single
p = ""
For i = 1 To k
Q$ =Str$ (A)
P$ = P$ + Q$
Next i
S = Val (P$)
H = H + S
Item = H
End Function
第二步：调试并运行程序。
第三步：按题目要求存盘。