Imports System.Threading
Module Module1
Sub Main()
'test code
'Dim a, b As Integer
'a = 3
'b = 4
'Exchange(a, b)
'Console.WriteLine("a=" & a & ", b=" & b)
Dim int_array(19) As Integer
Dim maxValIndex As Integer
Dim startIdx As Integer '開始位置
Dim rnd As New Random
Console.WriteLine("原始數組：")
'填充數組元素
For i As Integer = 0 To int_array.Length - 1
int_array(i) = rnd.Next(0, 500)
Console.Write(int_array(i) & ", ")
Thread.Sleep(150)
Next
'選擇法排序（降序）
startIdx = 0 '默認從第一個元素開始比較
Do
maxValIndex = startIdx '默認第一個元素最大
maxValIndex = GetMaxValIdx(int_array, maxValIndex, startIdx) '求數組中最大值得下標
If (maxValIndex <> startIdx) Then
Exchange(int_array(maxValIndex), int_array(startIdx))
End If
startIdx += 1
Loop While (startIdx < int_array.Length - 1)
Console.WriteLine(vbCrLf & "排序之後：")
For i As Integer = 0 To int_array.Length - 1
Console.Write(int_array(i) & ", ")
Next i
Console.ReadKey()
End Sub
'求數組中最大值得下標，遞歸函數
Public Function GetMaxValIdx(ByVal array() As Integer, ByVal maxValIdx As Integer, ByVal startIdx As Integer) As Integer
For i As Integer = startIdx To array.Length - 1
If (i <> maxValIdx) Then
If array(i) > array(maxValIdx) Then
Return GetMaxValIdx(array, i, startIdx)
End If
End If
Next
Return maxValIdx
End Function
'交換值
Public Sub Exchange(ByRef val1 As Integer, ByRef val2 As Integer)
Dim temp As Integer
temp = val1
val1 = val2
val2 = temp
End Sub
End Module
