Dim n As Integer Dim spec As String Const period As Integer = 4 Const maxerror As Double = 0.0000001 Dim payment(period) As Double '廣域變數 4 維度的陣列 Private Sub CommandButton1_Click()   Dim a, b, c, f, gap As Double   Dim loopNumber As Integer   n = n + 1 '第幾次計算+1   a = 0     '報酬率0   b = 1     '報酬率1   gap = 10   loopNumber = 10   payment(0) = TextBox1.Value   payment(1) = TextBox2.Value   payment(2) = TextBox3.Value   payment(3) = TextBox4.Value   f = npv(a)   If f = 0 Then      Label9.Caption = 0   ElseIf f < 0 Then      Label9.Caption = "內部報酬率小於 0."   Else      Do While gap > mexerror And Abs(f) > maxerror And loopNumber < 100        loopNumber = loopNumber + 1        c = (a + b) / 2        f = npv(c)        If Abs(f) > maxerror And gap >...