类型不匹配,缺少数组或用户定义类型.vb初学者，实在不知道该怎么解决

Dim n As Integer
Public Sub px(a() As Single)
Dim i, j As Integer
Dim t As Single
For i = 0 To (n - 2)
For j = (n - 1) To i
t = a(i): a(i) = a(j): a(j) = t
Next j
Next i
Print "转变后数组为：";
For i = 0 To (n - 1)
Print a(i);
Next i
End Sub
Private Sub Form_Click()
Dim i As Integer
Dim a(100) As Single
n = Val(InputBox("请输入您的数组长度："))
For i = 0 To (n - 1)
a(i) = CSng(InputBox("请输入第" + (i + 1) + "个元素的值："))
Next i
Print "转变前数组为：";
For i = 0 To (n - 1)
Print a(i);
Next i
px (a)
End Sub

下面的，错了吧，n第一句就定义了。sub pxa() as single 是个什么语法？
好像数组用作参数是有限制的，用sub px(a())，也许是sub px(a() as variant) ，也许是sub px(paramArray a() as variant)。
参数数组必须使用一个ParamArray关键字来指示，并声明为可变类型，而且只能是最后一个参数。

你好！ 第二行Public Sub px(a() As Single)错误 Public Sub pxa() As Single 第五行就出现的n你没定义过 希望对你有所帮助，望采纳。