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