1、算法说明
1)        加密解密
最简单的加密方法是：将每个字母加一序数，例如5，这时：
“A”→”F”,”a” →”f”,”B” →”G”,”b” →”g”……”Y” →”D”, ”y” →”d”,”Z” →”E”, ”z” →”e”
解密是加密的逆操作。 
代码如下：
                  Option Explicit
                  Private Sub Command1_Click()
                        Dim strInput$, Code$, Record$, c As String * 1
                        Dim i%, length%, iAsc%
                        strInput = Text1.Text
                        length = Len(Trim(strInput))
                        Code = ""
                        For i = 1 To length
                              c = mid(strInput, i, 1)
                              Select Case c
                                   Case "A" To "Z"
                                         iAsc = Asc(c) + 5
                                         If iAsc > Asc("Z") Then iAsc = iAsc - 26
                                         Code = Code & Chr(iAsc)
                                   Case "a" To "z"
                                         iAsc = Asc(c) + 5
                                         If iAsc > Asc("z") Then iAsc = iAsc - 26
                                         Code = Code & Chr(iAsc)
                                   Case Else
                                         Code = Code & c
                              End Select
                        Next i
                        Text2.Text = Code
                  End Sub
                  Private Sub Command3_Click()
                  Text1.Text = ""
                  Text2.Text = ""
                  Text3.Text = ""
                  Text1.SetFocus
                  End Sub

2、实战练习
1)        补充代码（2003秋二（8））
         下面程序的功能是统计文件中英文字母（不区分大小写）出现的个数。
                  Option Base 1
                  Private Sub Command1_Click()
　　　　            Dim alpha(26) As Integer,n As Integer
　　　　            Dim i As Integer,s As String
　　　　            Open "c:\kav2003\readme.txt" For Input As #11
　　　　            Do While Not EOF(11)
　　　　                     s=  （1） 
　　　　　　　　     s=UCase(s)
　　　　　　　　     If s>="A" And s<="Z" Then
　　　　　　　　　　      n=  （2） 
　　　　　　　　　　      alpha(n)=alpha(n)+1
　　　　　　　　     End If
　　　　            Loop
　　　　            For i=1 To 26
　　　　　　             If alpha(i)<>0 Then
　　　　　　　　              List1.AddItem Chr(i+64)&":"&CStr(alpha(i))
　　　　　　             End If
　　　　            Next i
　　　　            Close
                  End Sub
 
 
2)        补充代码（2000秋二（6））
         下面程序的功能是：统计当前盘当前文件夹中的顺序文件data.txt中共有多少个单词，约定连续出现的字母定义为一个单词。
                Option Explicit
 
 
                  Private Sub Form_Click()
                           Dim Char() As String, St As String, Tem As String
                           Dim Idx As Integer, Js As Long, Flen As Long
                           Dim F As Boolean, W As String * 1
                             （1） 
                           Flen = LOF(10)
                           St = Input(Flen, #10)
                           Js = 1
                           Do While Js <= Flen＋1
                                    W = Mid(St, Js, 1)
                                    If   （2）   Then
                                             Tem = Tem + W
                                             F = True
                                    ElseIf F = True Then
                                             Idx = Idx + 1
                                             ReDim Preserve Char(Idx)
                                             Char(Idx) = Tem
                                             Tem =  （3） 
                                             F = False
                                    End If
                                      （4） 
                           Loop
                           Print "共有"; Idx; "个单词"
                           For Js = 1 To Idx
                                    Print Char(Js)
                           Next Js
                  End Sub