第14課: VB的用户定義函數

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14.1 建立用户定義的VB 函數

函數的基本語法如下：

Public Function functionName (Arg As dataType,..........) As dataType

或

Private Function functionName (Arg As dataType,..........) As dataType

* Public表明該函數是適用於整個程序，

Private 則表明該函數適用於某個模塊或子程序。

範例 14.1

在這個范例裡，用戶可以計算某數額金錢的未來值（FutureValue， FV), 輸出屏幕如圖14.1 所示。

圖14.1

程式碼

Public Function FV(PV As Variant, i As Variant, n As Variant) As Variant

'計算未來值（FV-Future Value）的公式

'PV 代表 Present Value （現值）
FV = PV * (1 + i / 100) ^ n

End Function

Private Sub compute_Click()

Dim FutureVal As Variant
Dim PresentVal As Variant
Dim interest As Variant
Dim period As Variant
PresentVal = TxtPV.Text
interest = TxtRate.Text
period = TxtYears.Text
FutureVal = FV(PresentVal, interest, period)
LblFV.Caption=FutureVal

End Sub

範例 14.2

以下函數將自動計算學生獲得的考試分數和等級，輸出屏幕如圖14.2 所示。

程式碼
Public Function grade(mark As Variant) As String
Select Case mark
Case Is >= 80
grade = "A"
Case Is >= 70
grade = "B"
Case Is >= 60
grade = "C"
Case Is >= 50
grade = "D"
Case Is >= 40
grade = "E"
Case Else
grade = "F"
End Select

End Function
Private Sub compute_Click()
Lbl.Caption = grade(txtMark)

End Sub

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