[VBA ] 發生"溢位"問題

[tnt0619 ()]

請問一下,
當我單獨執行 function pvpv的時候,輸入變數可以得到結果;
但當我利用sub中呼叫function的時候,
就會在以下程式碼中的
     j = j + Round(CF / ((1 + r) ^ i), 2)
出現錯誤訊息,"溢位"
是不是我的sub觀念弄錯了,請高手指正,謝謝.
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Sub countpv()
 CF = InputBox("enter the cash flow value", "pv calc", "100")
 Worksheets("sheet1").Cells(2, 2) = CF
 r = InputBox("enter the interest rate", "pv calc", "0.01")
 Worksheets("sheet1").Cells(3, 2) = r
 n = InputBox("cash flow entered:" & CF & Chr(10) & _
   "interest rate entered " & FormatPercent(r, "2") & Chr(10) & _
   "enter the number of periods : ", "pv calc", "10")
 Worksheets("sheet1").Cells(4, 2) = n
 Call pvpv(CF, r, n)

End Sub
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    Function pvpv(CF, r, n) As Double
        Dim i, j As Double
        i = 1
        j = 0
         Do While i <= n
          j = j + Round(CF / ((1 + r) ^ i), 2)
          i = i + 1
         Loop
        pvpv = j
        MsgBox "the pv is :" & pvpv, vbOKOnly, "pv calc"
        Worksheets("sheet1").Cells(5, 2) = pvpv
    End Function
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