题目

编写“构造字符串”程序，实现如下功能：输入不重复的N个字符（2≤N≤5）,构造由该N个字符（允许重复）组成的N位的字符串，输出所构造的字符串及构造的方法种数。程序运行界面如图所示。实现上述功能的VB代码如下：Private Sub Command1_Click() Dim a(0 To 4) As String Dim b(0 To 4) As IntegerDim s As String, r As StringDim i As Integer, j As Integer, k As Integer, c As Integer, n As IntegerList1.Clears = Text1.Text :n = Len(s)IfThen '选填 Label1.Caption = 数据输入有误！Exit Sub'退出 End IfFor i = 0 To n -