Question

我很困惑地改变了我从数据库中显示的问题的逻辑。我当前的代码显示文本框中的随机问题，但它也显示空和重复的条目。

    Dim r As MySqlDataReader
    Dim i As Integer = 0
    Dim temp() As Integer = {}


    Dim txtQ() As TextBox = {txtQ1, txtQ2, txtQ3, txtQ4, txtQ5, txtQ6, txtQ7, txtQ8, txtQ9, txtQ10}
    Dim cbA() As CheckedListBox = {cbA1, cbA2, cbA3, cbA4, cbA5, cbA6, cbA7, cbA8, cbA9, cbA10}

    con.Open()
    cmd = New MySqlCommand("select * from tbexam", con)
    r = cmd.ExecuteReader


    While r.Read
        If i <= 9 Then
            Randomize()
            Dim j As Integer = CInt(Int(9 * Rnd()))

            txtQ(j).Text = r.GetString("exam_question")
            cbA(j).Items.Clear()
            cbA(j).Items.Add("a) " & r.GetString("exam_ans_a"))
            cbA(j).Items.Add("b) " & r.GetString("exam_ans_b"))
            cbA(j).Items.Add("c) " & r.GetString("exam_ans_c"))
            cbA(j).Items.Add("d) " & r.GetString("exam_ans_d"))


            i = i + 1
        End If
    End While

Answer 1

当你在j中放置一个随机数时，它（非常接近）是0到9之间的一个随机数。这相当于滚动一个十边骰子。您认为如果您要将其滚动十次，您将获得0到9中的每一个中的一个值的可能性是多少？很低。你实际得到的是：2,0,8,2,5,1,7,6,1,4。这个序列包含2和1的重复，并且不出现值3和9。这就是你的重复和差距来自的地方。

您可以尝试的一个选项是按顺序填充数组，然后将其随机播放。

Dim r As MySqlDataReader
Dim i As Integer = 0
Dim temp() As Integer = {}

Dim txtQ() As TextBox = {txtQ1, txtQ2, txtQ3, txtQ4, txtQ5, txtQ6, txtQ7, txtQ8, txtQ9, txtQ10}
Dim cbA() As CheckedListBox = {cbA1, cbA2, cbA3, cbA4, cbA5, cbA6, cbA7, cbA8, cbA9, cbA10}

con.Open()
cmd = New MySqlCommand("select * from tbexam", con)
r = cmd.ExecuteReader

' Read the Q&As into the arrays in the order they appear in the DB
While r.Read
    If i <= 9 Then
        txtQ(i).Text = r.GetString("exam_question")
        cbA(i).Items.Clear()
        cbA(i).Items.Add("a) " & r.GetString("exam_ans_a"))
        cbA(i).Items.Add("b) " & r.GetString("exam_ans_b"))
        cbA(i).Items.Add("c) " & r.GetString("exam_ans_c"))
        cbA(i).Items.Add("d) " & r.GetString("exam_ans_d"))
        i = i + 1
    End If
End While

' Re-order the arrays by swapping each element with another, randomly selected element.
' Start with i at the count of the elements read in the last loop and work down.
Dim n as Integer = i - 1
While i > 0
    Dim j As Integer = CInt(Int(n * Rnd()))
    i = i - 1
    ' Swap elements i and j of the arrays
    Dim tmpQ As TextBox = txtQ(i)
    txtQ(i) = txtQ(j)
    txtQ(j) = tmpQ
    Dim tmpA() As CheckedListBox = cbA(i)
    cbA(i) = cbA(j)
    cbA(j) = tmpA
End While

这可以简化和抽象，但你明白了。

Answer 2

使用随机数生成很难避免重复输入，但您可以避免空条目。你得到空条目，因为你生成随机数并用该id获取问题，不幸的是，id始终在数据库中不可用。首先，从数组中的数据库中获取所有ID，并生成从0到数组长度的随机数。并选择数组键的id值。

随机和随机问题vb

2 个答案: