帮我看看这里出了什么问题

For m = 1 To 6
For n = 1 To 6
For c = 1 To 8
If Controls("TextBox" & n & m).Text And Controls("TextBox" & c).Text = "" Then
MsgBox "不能为空!"
Exit Sub
Exit For
End If
请教老师及同窗，关于Controls("TextBox" & n & m).Text = "" And Controls("TextBox" & c).Text = ""不能同时运行，只运行了其中一个条件的问题怎么解决