照着书打了段程序，仔细对了没有问题，但是运行不起来，希望高手指点一下！！！谢谢

Dim st As String
Private Sub copy_click()
st = txtNoteEdit.SelText
copy.Enabled = False
cut.Enabled = False
paste.Enabled = True
End Sub

Private Sub cut_click()
st = txtNoteEdit.SelText
txtNoteEdit.SelText = ""
copy.Enabled = False
cut.Enabled = False
paste.Enabled = True
End Sub

Private Sub delete_Click()
Text1.Text = ""
Text2.Text = ""
End Sub

Private Sub exit_Click()
End
End Sub

Private Sub paste_Click()
txtNoteEdit.SelText = st
End Sub

Sub txtnoteedit_mousemove(button As Integer, shift As Integer, X As Single, y As Single)
If txtNoteEdit.seltxt <> "" Then
copy.Enabled = True
cut.Enabled = True
paste.Enabled = False
Else
copy.Enabled = True
cut.Enabled = True
paste.Enabled = False
End If
End Sub

Dim st As String
Private Sub copy_click()
st = txtNoteEdit.SelText

我明明已经定义了st 但是运行是说st = txtNoteEdit.SelText有问题

我照着大学教材打的应该不会错吧