我想知道如果用户想返回上一个问题，系统如何识别该问题。如果已经回答，则答案将更新，或者分数增加或不增加，或者如果答案未编辑，则分数相同。
BUTTON1将返回上一个问题 Button2用于检查答案是否为真 按钮3用于继续考试
Imports MySql.Data.MySqlClient
Imports System.Drawing
Imports System.IO
Public Class Exam
'declaring variables for connection'
Dim score As Integer
Dim rightans As String
Dim correct As Integer = 0
Dim choice As String
Dim choice1 As String
Dim choice2 As String
Dim choice3 As String
Dim con As MySqlConnection
Dim con1 As MySqlConnection
Dim COMMAND As MySqlCommand
Dim read As MySqlDataReader
Dim da As MySqlDataAdapter
Dim sql As String
Private Sub Exam_Load(sender As Object, e As EventArgs) Handles MyBase.Load
'setting the radiobutton to false, so that when the form load there is no shaded button'
Label2.Text = 1
A.Checked = False
B.Checked = False
C.Checked = False
D.Checked = False
con = New MySqlConnection
Button1.Enabled = False
con.ConnectionString = "server=localhost;userid=root;password=;database=user;"
'calling sub
qno()
End Sub
Sub clear()
'to set the radiobutton false/no shaded.
A.Checked = False
B.Checked = False
C.Checked = False
D.Checked = False
End Sub
Sub qno()
'calling connection'
Try
con = New MySqlConnection
con.ConnectionString = "server=localhost; user id=root; password=; database=user;"
con.Open()
sql = "SELECT * FROM user.math WHERE question_id = @ID;"
COMMAND = New MySqlCommand
With COMMAND
.Connection = con
.CommandText = sql
.Parameters.Clear()
.Parameters.AddWithValue("@ID", Label2.Text)
.ExecuteNonQuery()
End With
Dim arrImage() As Byte
Dim dt As New DataTable
da = New MySqlDataAdapter
da.SelectCommand = COMMAND
da.Fill(dt)
If dt.Rows.Count > 0 Then
arrImage = dt.Rows(0).Item(7)
Dim mstream As New System.IO.MemoryStream(arrImage)
Pic1.Image = Image.FromStream(mstream)
question.Text = dt.Rows(0).Item(1)
A.Text = dt.Rows(0).Item(2)
B.Text = dt.Rows(0).Item(3)
C.Text = dt.Rows(0).Item(4)
D.Text = dt.Rows(0).Item(5)
Else
MsgBox("No results!")
End If
Catch ex As MySqlException
MsgBox(ex.Message)
Finally
con.Close()
da.Dispose()
End Try
End Sub
Sub increment()
'incrementing the score f the answer is correct'
Dim i As Integer = 0
i = Label2.Text
i = i + 1
Label2.Text = i
If Label2.Text > 1 Then
Button1.Enabled = True
End If
End Sub
Sub decrement()
'incrementing the score f the answer is correct'
Dim i As Integer = 1
i = Label2.Text
i = i - 1
Label2.Text = i
If Label2.Text = 1 Then
Button1.Enabled = False
End If
End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
'checking of the user answer the questions'
If ((A.Checked = False) And (B.Checked = False) And (C.Checked = False) And (D.Checked = False)) Then
MsgBox("Please answer the question")
Else
'if the examinee answers all the examination it will call another questions from database'
If A.Checked = True Then
con.Open()
' Dim ans As String
Dim arren As String = "A"
Dim sql As String = ("select answer from user.math where question_id = '" & Label2.Text & "' ")
COMMAND = New MySqlCommand(sql, con)
Dim it As String
read = COMMAND.ExecuteReader
If read.HasRows Then
If read.Read Then
it = read.Item("answer")
If it = choice Then
correct = correct + 1
Label4.Text = correct
ElseIf it <> choice And Label2.Text <= 1 Then
correct = correct - 1
Label4.Text = correct
End If
End If
clear()
End If
If Label2.Text = 10 Then
MessageBox.Show("proceed to other subject test")
End If
con.Close()
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
decrement()
qno()
End Sub
End Class
答案 0 :(得分：0)
未经测试，因为我没有您的数据库。以上和内嵌评论。
Public Class Form3
Dim correct As Integer = 0
Private Sub Exam_Load(sender As Object, e As EventArgs) Handles MyBase.Load
'setting the radiobutton to false, so that when the form load there is no shaded button'
Label2.Text = "1"
A.Checked = False
B.Checked = False
C.Checked = False
D.Checked = False
Button1.Enabled = False
qno()
End Sub
Private Sub clear()
'to set the radiobutton false/no shaded.
A.Checked = False
B.Checked = False
C.Checked = False
D.Checked = False
End Sub
Private Sub qno()
Try
'Using...End Using blocks will close and dispose of your objects
Using con = New MySqlConnection("server=localhost;userid=root;password=;database=user;")
Using Cmd = New MySqlCommand("SELECT * FROM user.math WHERE question_id = @ID;", con)
Cmd.Parameters.AddWithValue("@ID", Label2.Text)
Dim arrImage() As Byte
Dim dt As New DataTable
Using da = New MySqlDataAdapter
da.SelectCommand = Cmd
da.Fill(dt)
If dt.Rows.Count > 0 Then
'Not at all sure about this picture code
arrImage = CType(dt.Rows(0).Item(7), Byte())
Dim mstream As New System.IO.MemoryStream(arrImage)
Pic1.Image = Image.FromStream(mstream)
question.Text = dt.Rows(0).Item(1).ToString
A.Text = dt.Rows(0).Item(2).ToString
B.Text = dt.Rows(0).Item(3).ToString
C.Text = dt.Rows(0).Item(4).ToString
D.Text = dt.Rows(0).Item(5).ToString
'guessing that answer it item 6
HiddenLabel.Text = dt.Rows(0).Item(6).ToString
Else
MsgBox("No results!")
End If
End Using
End Using
End Using
Catch ex As MySqlException
MsgBox(ex.Message)
End Try
End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
'checking of the user answer the questions'
If ((A.Checked = False) And (B.Checked = False) And (C.Checked = False) And (D.Checked = False)) Then
MsgBox("Please answer the question")
Exit Sub
End If
'The correct answer was put in the HiddenLabel.Text (Visible set to False)
'in the qno Sub
Dim CorrectAnswer As String = HiddenLabel.Text
Dim UserChoice As String = ""
If A.Checked Then
UserChoice = "A"
ElseIf B.Checked Then
UserChoice = "B"
ElseIf C.Checked Then
UserChoice = "C"
Else
UserChoice = "D"
End If
If UserChoice = CorrectAnswer Then
correct += 1
Else
'It is very hard to get a good score if it is decremented with every wrong answer
'Why not skip this and just give a zero for a wrong answer
correct -= 1
End If
Label4.Text = correct.ToString
clear()
If Label2.Text = "10" Then
MessageBox.Show("proceed to other subject test")
Me.Hide()
exam2.Show()
Else
'Add code to keep track of question number in
'Add code to show the next question
End If
End Sub