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

就是刚生成的a(i)与以前生成的字符去校对，如果有相同的，就 重新生成一个，为什么会i=i-1，是因为next语句会自动+1的，所以先-1。在j循环里正常执行完了，是没有i=i-1的，这样next i后，才生成下一个字母。

给一个简单的生成不重复26个字母的代码：

Private Sub Command2_Click()
    Dim a(25) As String, i As Integer, j As Integer, st As String
    st = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    For i = 25 To 0 Step -1
        j = Rnd() * i + 1
        a(i) = Mid(st, j, 1)
        st = Replace(st, a(i), "")
        Print a(i);
    Next
    Print
End Sub

新生成的和已经生成的一一对比，如果有，就再生成一个，如果没有，这个就生成了