替自定义函数设置可选参数

本文为《别怕，Excel VBA其实很简单（第3版）》随书问题参考答案

Function JoinText(Rng As Range, Optional Txt As String = "，") As String
Dim c As Range
For Each c In Rng
JoinText = JoinText & c.Value & Txt
Next c
JoinText = Left(JoinText, Len(JoinText) - 1)
End Function

或者

Function JoinText(Rng As Range, Optional Txt As Variant) As String
Dim c As Range
If IsMissing(Txt) Then Txt = "，"
For Each c In Rng
JoinText = JoinText & c.Value & Txt
Next c
JoinText = Left(JoinText, Len(JoinText) - 1)
End Function