题目

【加试题】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17所示）。实现上述功能的VB代码如下：  Dim m2 As StringPrivate Sub Command1Click()Dim flag(1 To 26) As BooleanDim num As Integer,t As IntegerRandomizenum = 1Text3.Text = " "For i = 1 To 26    flag(i) = FalseNext iDo While num <= 26    x = Int(Rnd * 26) + 97          ①           If  flag(t) = False Then    m2 = m2 + Chr(x)    num = num + 1      ②           End IfLoopText3.Text = m2End SubPrivate Sub Command2Click()Dim s As String， m As String， result As StringDim k As String， c As Integers = Text1.Textm = "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       ③           If k = Mid(m, c, 1) Then    continue = False    End If    c = c + 1    Loop   ④     Next iText2.Text = resultEnd Sub程序①处的代码是程序②处的代码是程序③处的代码是程序④处的代码是 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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