Visual Basic 自动售货机

Question

我已经开始使用 Visual Basic 编写自动售货机代码。它到目前为止有效，但我希望它在你买不起东西时提出错误消息。它仍然是相当基本的，还没有任何项目，但在我开始做其他事情之前希望这不会妨碍我。目前，“Then”语句出现错误，不知道如何解决。我再次对它很陌生，并提出任何建议。谢谢。

Public Class Form1

Private Sub BuyButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BuyButton.Click

    Dim Cost, Amount, Change As Decimal
    Dim Pennies, Pounds As Integer
    Dim msg As String

    Cost = Decimal.Parse(CostTextBox.Text)
    Amount = Decimal.Parse(AmountTextBox.Text)
    Change = (Amount - Cost) * 10

    Pounds = Change \ 10
    Change = Change Mod 10

    Pennies = Change \ 10
    Change = Change Mod 10

    If Change = "Your change is: -" Then

        msg = "You don't have enough Money"

    Else

        msg = "Your change is: " & Change & vbNewLine
        msg += "Pennies: " & Pounds & vbNewLine
        msg += "Pounds: " & Pennies & vbNewLine

    End If

    ChangeLabel.Text = msg

End Sub
End Class

我用过的解决方案： 公开课形式1

Private Sub BuyButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BuyButton.Click

    Dim Cost, Amount, Change As Decimal
    Dim Pennies, Pounds As Integer
    Dim msg As String

    Cost = Decimal.Parse(CostTextBox.Text)
    Amount = Decimal.Parse(AmountTextBox.Text)
    Change = (Amount - Cost)

    If Change < 0 Then

        msg = "You don't have enough Money"
        AmountTextBox.Text = Change + Cost

    Else

        AmountTextBox.Text = Change
        Pounds = Math.Floor(Change)
        Pennies = (Change - Pounds) * 100

        msg = "Your change is: " & Change.ToString("##.00") & Environment.NewLine
        msg += "Pounds: " & Pounds & vbNewLine
        msg += "Pennies: " & Pennies & vbNewLine

    End If
    ChangeLabel.Text = msg
End Sub

Answer 1

首先，检查是否有足够的钱，检查零钱是否小于 0 - If Change <0 Then ...。其次，您将Change 更改为Change = Change mod 10，因此最终您不会得到正确的结果。第三，更容易将 Change 设为整数。要获得最后两位零钱（便士），您应该使用Pennies=Change mod 100，要获得其他数字（英镑），您应该使用Pounds=Change\100。第四，您在创建消息时交换了英镑和便士。最后，如果有零钱，您只需将零钱分成英镑和便士。

Public Class Form1

Private Sub BuyButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BuyButton.Click

    Dim Amount, Change As Decimal
    Dim Cost, Pennies, Pounds As Integer
    Dim msg As String

    Cost = Decimal.Parse(CostTextBox.Text)
    Amount = Decimal.Parse(AmountTextBox.Text)
    Change = (Amount - Cost) * 100

    If Change < 0 Then

        msg = "You don't have enough Money"

    Else

        Pounds = Change \ 100
        Pennies = Change Mod 100
        msg = "Your change is: " & Change & vbNewLine
        msg += "Pounds: " & Pounds & vbNewLine
        msg += "Pennies: " & Pennies & vbNewLine

    End If

    ChangeLabel.Text = msg

End Sub
End Class

Answer 2

如果我是你，我会考虑精简一下。停止除以 10 再乘以 10 - 这对您的事业没有帮助。去做这样的事情。

Dim Cost, Amount, Change As Decimal
    Dim Pennies, Pounds As Integer
    Dim msg As String

    Cost = Decimal.Parse(CostTextBox.Text)
    Amount = Decimal.Parse(AmountTextBox.Text)
    Change = (Amount - Cost)  --Work in pounds

    If Change < 0 Then

        msg = "You don't have enough Money"

    Else

        Pounds = Math.Floor(Change)
        Pennies = (Change - Pounds) * 100  --Multiply pounds by 100 to get pence

        --Environment.NewLine is the preferred way to insert a newline which will
        --always be correct for the environment.
        msg = "Your change is: " & Change.ToString("##.00") & Environment.NewLine --Note the .ToString("##.00") - this tells VB to convert the number to a string and show two decimal places
        msg += "Pounds: " & Pounds.ToString() & Environment.NewLine
        msg += "Pennies: " & Pennies.ToString() & Environment.NewLine

    End If

    ChangeLabel.Text = msg

不惜一切代价避免隐式转换。是的，Pounds = Change / 10 有效，但它是一种隐含的缩小范围，可能无法按照您的预期工作。我们在这里使用Math.Floor 的原因是因为我们想要小数的整数部分，这就是Math.Floor 所做的 - 为您提供等于或小于所提供值的最大整数。

还要注意Change.ToString 的使用——所有内在类型都派生自超类型Object，这意味着它们实现了ToString 方法。这将为您提供对象值的显式转换字符串表示形式，您可以通过提供掩码（括号中的"##.00#"bit）对其应用格式设置。 Have a look at the MSDNpage on the subject 了解有关将自定义格式应用于字符串的更多信息。

Answer 3

If Change = "Your change is: -" Then

更改值应该等于一个值，而不是一个字符串，这需要更改为类似

If change < 0 Then

通常当我使用& 操作符时，我不太确定 =+ 版本是否有效（我从未尝试过）

msg = msg &  "Pennies: " & Pounds & vbNewLine
msg = msg & "Pounds: " & Pennies & vbNewLine