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计算机等级考试二级VB常用算法(8)：排序
作者：佚名  文章来源：不详  点击数  更新时间：2008/4/18 14:45:44  文章录入：杜斌  责任编辑：杜斌

1、算法说明
1)      顺序查找
         逐个元素找，如果有，则记录位置，然后跳出循环；否则，查找失败。
         代码如下：
                  Private Sub Search(a(), ByVal Key, Index As Integer)
                        Dim i%
                        For i = LBound(a) To UBound(a)
                              If a(i) = Key Then '找到，将元素下标保存在index中并结束查找
                                       Index = i
                                       Exit Sub
                              End If
                        Next i
                        Index = -1             '若没找到，则index值为-1
                  End Sub    
2)      二分法查找
顺序查找效率低下，当数组有序排列时，可以使用二分法查找提高效率。
         算法思想：
　　代码如下：
                  Private Sub birSearch(a(), ByVal low%, ByVal high%, ByVal Key, index%)
                        Dim mid As Integer
                        If low > high Then     '没有查找到
                              index = -1
                              Exit Sub
                        End If
                        mid = (low + high) \ 2 '取查找区间的中点
                        If Key = a(mid) Then   '查找到，返回下标
                              index = mid
                              Exit Sub
                        ElseIf Key < a(mid) Then '查找区间在上半部分
                          high = mid - 1
                     Else
                          low = mid + 1    '查找区间在下半部分
                        End If
                        Call birSearch(a, low, high, Key, index) '递归调用查找函数
                  End Sub
调用方法：
                  Private Sub Command1_Click()
                        Dim a(11)
                        a(1) = 5: a(2) = 13: a(3) = 19: a(4) = 21: a(5) = 37
                        a(6) = 56: a(7) = 64: a(8) = 75: a(9) = 80: a(10) = 88: a(11) = 92
                        Dim ind As Integer
                        Call birSearch(a, LBound(a), UBound(a), 21, ind)
                        Print ind
                  End Sub


2、实战练习        补充代码（2002春二（9））
         C盘根目录下stu.txt文件中以下的格式保存着学生姓名及班号信息。本程序的功能是：读取该文件中的数据，再利用InputvBox输入要查找的学生姓名，通过顺序查找，给出找到或找不到的信息。附图是某同学被找到时显示的信息窗口。
        张文，机械01
        李明，机械01
        王文卉，机械01
        …
        何宇宙，电子02     
    　　　Option Explicit 
                 Option Base 1
                  Private Sub Form_click()
                           Dim stu() As String, glass() As String, i As Integer
                           Dim n As Integer, name As String, k As Integer
                           Open "c:\stu\stu.txt" For Input As #11
                           Do While （1）
                                    （2）
                                    ReDim Preserve stu(n), glass(n)
                                    Input #11, stu(n), glass(n)
                           Loop
                           name = InputBox("输入欲查找的学生姓名：")
                           Call search(name, stu, k)
                           If k <= n Then
                                    MsgBox （3）
                           Else
                                    MsgBox "无此人。"
                           End If
                           Close #11
                  End Sub
                  Private Sub search(name As String, stu() As String, k As Integer)
                           Dim i As Integer
                           For i = 1 To UBound(stu)
                                    If name = stu(i) Then
                                             （4）
                                    End If
                           Next i
                           （5）
                  End Sub
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