Question

vb程序设计代码完善：编制程序从输入的字符串中删除重复出现的字母（小写字母需转换为大写字母）

然后在列表框中降序显示所有出现的字母
Option Base 1
Option Explicit
Private Sub Command1_Click()
Dim a(26) As Integer, i As Integer, s As String
Dim t As String, idx As Integer, s1 As String
s = UCase(Text1)
For i = 1 To Len(s)
t = Mid(s, i, 1)
If Then

If a(idx) <> 1 Then
s1 = s1 & t

End If
Else
s1 = s1 & t
End If
Next i
Text2 = s1
For i = 26 To 1 Step -1
If a(i) = 1 Then List1.AddItem Chr(Asc("a") + i - 1)
Next i
End Sub

Answer 1

Option Base 1
Option Explicit
Private Sub Command1_Click()
  Dim a(26) As Integer, i As Integer, s As String
  Dim t As String, j As Integer
  s = UCase(Text1)
  i = 1
  While i < Len(s)
    t = Mid(s, i, 1)
    If t >= "A" And t <= "Z" Then
      a(Asc(t) - Asc("A") + 1) = 1
      j = i + 1
      While j <= Len(s)
        If Mid(s, j, 1) = t Then
          s = Left(s, j - 1) & Mid(s, j + 1)
        Else
          j = j + 1
        End If
      Wend
    End If
    i = i + 1
  Wend
  Text2 = s
  For i = 26 To 1 Step -1
    If a(i) = 1 Then List1.AddItem Chr(Asc("A") + i - 1)
  Next i
End Sub

Answer 2

If        Then
   idx = asc(t) - 64
   If a(idx) <> 1 Then
      s1 = s1 & t
      a(idx) = 1
   End If
Else
   s1 = s1 & t
End If

想了半天没想出来上面的IF和后面的ELSE有什么用,删除重复应该也不是这么写啊...