求大神翻译下，这段代码是如何生成不重复的26个英文字母？
搞不明白for j = 0 后面是怎么样的Private Sub Command1_Click()
Dim a(25), i As Integer, j As Integer, s As String, length As Integer, c As String
Dim t
Randomize
For i = 0 To 25
a(i) = Chr(Int(Rnd() * 26 + 65))
For j = 0 To i - 1
If a(i) = a(j) Then
i = i - 1
Exit For
End If
Next j
Next i
