第一个for循环中随机函数Rnd()为什么反回的值总一样？

[lovelovevb]

Module Module1

Sub Main()
Dim RandomArray(20) As Single
Dim SortedArray(20) As Single
Dim Rndstring As String
Dim Rnds As Single
Dim iCount, jCount, kCount As Integer
Console.WriteLine("产生的随机数列为：")
For iCount = 1 To 20
Rnds = Rnd() * 9999 + 1
Rndstring = Format(Rnds, "###0.00")
Rnds = CSng(Rndstring)
RandomArray.SetValue(Rnds, iCount)
Console.WriteLine(Convert.ToString(RandomArray.GetValue(iCount)) & ",")
Next
'插入法排序
SortedArray(1) = RandomArray(1)
For iCount = 2 To 20
SortedArray(iCount) = RandomArray(iCount)
For jCount = 1 To iCount - 1
If RandomArray(iCount) < SortedArray(jCount) Then
For kCount = iCount - 1 To jCount Step -1
SortedArray(kCount + 1) = SortedArray(kCount)
Next
SortedArray(jCount) = RandomArray(iCount)
Exit For
End If
Next
Next
Console.WriteLine("排好序的数列是：")
For iCount = 1 To 20
Console.WriteLine(Convert.ToString(SortedArray.GetValue(iCount)) & ",")
Next
Console.WriteLine()
'利用数组对象排序
RandomArray.Sort(RandomArray)
Console.WriteLine("排好序的数组是：")
For iCount = 1 To 20
Console.WriteLine(Convert.ToString(RandomArray.GetValue(iCount)) & ",")
Next
Console.WriteLine()
Console.Read()
End Sub

End Module
第一个for循环中随机函数Rnd()为什么反回的值总一样？而有时却又不一样！

[lovelovevb]

Module Module1
Function IsPrimeNumber(ByVal pNumber) As Boolean
Dim iFactor As Integer
For iFactor = 2 To Int(Math.Sqrt(pNumber))
If pNumber Mod iFactor = 0 Then
Return False
End If
Next
Return True
End Function
--------------------------------------------------------------------------------------
Sub Main()
Dim NArray(20), PArray(0) As Integer
Dim iCount, Rnds As Integer
Randomize()
Console.WriteLine("生成的10000以内的随机数列是：")
'利用循环生成随机数列，存放在数组中
For iCount = 0 To 20
Rnds = Int(Rnd() * 9998) + 2
NArray.SetValue(Rnds, iCount) '= NArray (iCount) = Rnds
Console.Write(Convert.ToString(NArray.GetValue(iCount)) & ",")
Next
Console.WriteLine()
'利用循环判断数组中的质数
For iCount = 0 To 20
If IsPrimeNumber(NArray.GetValue(iCount)) Then
ReDim Preserve PArray(PArray.GetUpperBound(0) + 1) '将质数添加进数组
PArray.SetValue(NArray.GetValue(iCount), PArray.GetUpperBound(0))
End If
Next
Console.WriteLine("数列中的质数有：{0:###}个", PArray.GetLength(0) - 1)
For iCount = 1 To PArray.GetUpperBound(0)
Console.Write(PArray.GetValue(iCount))
Console.Write(",")
Next
Console.WriteLine()
Console.ReadLine()
End Sub

End Module

这个主函数中第一个for循环中随机函数Rnd()为什么返回的值不一样？

[AntingZ]

在使用Rnd()之前加上下面的Randomize语句将 Rnd 函数的随机数生成器初始化，并给它一个新的种子值

Console.WriteLine("产生的随机数列为：")
Randomize
For iCount = 1 To 20
...
Next

[AntingZ]

详情请参考MSDN:

http://msdn.microsoft.com/library/chs/default.asp?url=/library/CHS/vblr7/html/vastmrandomize.asp

http://msdn.microsoft.com/library/chs/default.asp?url=/library/CHS/vblr7/html/vafctrnd.asp

[zhilunchen]

需用Randomize初始随机数发生器