Private Sub Command1_Click()
Dim a As Long, m As Long
m = 100
a = 10
mysub1 m, 3   '有参数
mysub1 a     '没有参数
End Sub

Private Sub mysub1(ByVal n As Long, Optional val)   '这里怎么把 ByVal n As Long 改成 ByRef n As Long 效果一样?
n = n + 9
Dim s As String
If IsMissing(val) Then
s = "not pass 没有参数"
Else
s = "ok 有参数"
End If
MsgBox n & "," & s
End Sub

谢谢。