题目

编写VB程序，实现如下功能：单击“生成密文”按钮Command2，在文本框Text3中产生与每个小写字母对应的密文(每个明文字母对应1个不重复的密文字母)。在文本框Text1中输入单词字符串，单击“加密”按钮Command1后，进行逐个字符加密，加密方法：在“明文”中找到相应字符，再得到明文对应位置的密文，并在文本框Text2中显示对应密文(运行效果如图所示)。实现上述功能的VB代码如下，请完善程序代码。 Dim m2 As String Private Sub Command1_Click() Dim flag(1 To 26) As Boolean Dim num As Integer，t As Integer Randomize num = 1 Text3.Text = “” For i = 1 To 26  flag(i) = False Next i Do While num <= 26  x = Int(Rnd * 26) + 97    If flag(t) = False Then m2 = m2 + Chr(x) num = num + 1  End If Loop Text3.Text = m2 End Sub Private Sub Command2_Click() Dim s As String, m As String, result As String Dim k As String, c As Integer s = Text1.Text m = “abcdefghijklmnopqrstuvwxyz” For i = 1 To Len(s)  k = Mid(s, i, 1)  If k >= ”A” And k <= “Z”  Then k = Chr(Asc(k) + 32)  End If  c = 1: continue = True  Do While If k = Mid(m, c, 1) Then  continue = False End If c = c + 1  Loop   Next i Text2.Text = result End Sub 答案：【1】t = x - Asc(”a”) + 1【2】flag(t) = True【3】countinue = True 或countinue【4】result = result + Mid(m2, c - 1, 1)

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