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步骤 4：添加 CheckTheAnswer() 方法

测验需要验证用户的答案是否正确。幸运的是，编写执行简单计算的方法（如 CheckTheAnswer() 方法）并不难。

说明说明

对于使用 Visual Basic 的用户而言，有一点值得注意，由于此方法返回一个值，因此您将使用 Function 关键字来代替常见的 Sub 关键字。真的很简单：Sub 不会返回值，但函数会返回值。

添加 CheckTheAnswer() 方法

  1. 添加 CheckTheAnswer() 方法，该方法将 addend1 和 addend2 相加，并验证得到的和与 sum NumericUpDown 控件中的值是否相等。如果和相等，则此方法返回 true；否则返回 false。您的代码应类似以下内容。

    ''' <summary>
''' Check the answer to see if the user got everything right.
''' </summary>
''' <returns>True if the answer's correct, false otherwise.</returns>
''' <remarks></remarks>
Public Function CheckTheAnswer() As Boolean

    If addend1 + addend2 = sum.Value Then
        Return True
    Else
        Return False
    End If

End Function

    /// <summary>
/// Check the answer to see if the user got everything right.
/// </summary>
/// <returns>True if the answer's correct, false otherwise.</returns>
private bool CheckTheAnswer()
{
    if (addend1 + addend2 == sum.Value)
        return true;
    else
        return false;
}

    程序需要调用此方法以验证用户的答案是否正确。可以通过添加 if else 语句来做到这一点。该语句看起来类似下面这样。

    If CheckTheAnswer() Then
    ' statements that will get executed
    ' if the answer is correct 
ElseIf timeLeft > 0 Then
    ' statements that will get executed
    ' if there's still time left on the timer
Else
    ' statements that will get executed if the timer ran out
End If

    if (CheckTheAnswer())
{
      // statements that will get executed
      // if the answer is correct 
}
else if (timeLeft > 0)
{
      // statements that will get executed
      // if there's still time left on the timer
}
else
{
      // statements that will get executed if the timer ran out
}

  2. 接下来，修改计时器的 Tick 事件处理程序以检查答案。带有答案检查功能的新事件处理程序应包括以下内容。

    Private Sub Timer1_Tick() Handles Timer1.Tick

    If CheckTheAnswer() Then
        ' If the user got the answer right, stop the timer
        ' and show a MessageBox.
        Timer1.Stop()
        MessageBox.Show("You got all of the answers right!", "Congratulations!")
        startButton.Enabled = True
    ElseIf timeLeft > 0 Then
        ' Decrease the time left by one second and display
        ' the new time left by updating the Time Left label.
        timeLeft -= 1
        timeLabel.Text = timeLeft & " seconds"
    Else
        ' If the user ran out of time, stop the timer, show
        ' a MessageBox, and fill in the answers.
        Timer1.Stop()
        timeLabel.Text = "Time's up!"
        MessageBox.Show("You didn't finish in time.", "Sorry")
        sum.Value = addend1 + addend2
        startButton.Enabled = True
    End If

End Sub

    private void timer1_Tick(object sender, EventArgs e)
{
    if (CheckTheAnswer())
    {
        // If the user got the answer right, stop the timer 
        // and show a MessageBox.
        timer1.Stop();
        MessageBox.Show("You got all the answers right!",
                        "Congratulations");
        startButton.Enabled = true;
    }
    else if (timeLeft > 0)
    {
        // Decrease the time left by one second and display 
        // the new time left by updating the Time Left label.
        timeLeft--;
        timeLabel.Text = timeLeft + " seconds";
    }
    else
    {
        // If the user ran out of time, stop the timer, show
        // a MessageBox, and fill in the answers.
        timer1.Stop();
        timeLabel.Text = "Time's up!";
        MessageBox.Show("You didn't finish in time.", "Sorry");
        sum.Value = addend1 + addend2;
        startButton.Enabled = true;
    }
}

    此时，如果计时器的事件处理程序确认用户的答案正确，则该事件处理程序将停止计时器并显示祝贺消息，然后使**“开始”**按钮重新可用。

  3. 保存并运行程序。开始游戏，然后键入加法问题的正确答案。

    说明说明

    在键入答案时，您可能会注意到有关 NumericUpDown 控件的意外情况。如果在未选择整个答案的情况下开始键入，则原来的 0 将会保留，并且您必须手动将其删除。本教程后面将更正此情况。

  4. 当您键入正确答案之后，消息框将打开，**“开始”按钮将可用，并且计时器将停止。再次单击“开始”**按钮以确保此情况属实。

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