Visual Basic自动售货机

Question

我已经开始用Visual Basic编写自动售货机代码。到目前为止，它是有效的，但我希望它能在你买不起东西的时候给出一个错误消息。它仍然是相当基本的，上面还没有项目，但我希望在我开始任何其他东西之前，先把它弄清楚。目前，它为"Then“语句提出了一个错误，并且不知道如何修复它。再说一次，我对它非常陌生，并提出了任何建议。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

我使用过的解决方案:公共类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)

    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，为了检查是否有足够的钱，您可以检查零头是否小于0- If Change <0 Then ...。其次，您将使用Change = Change mod 10更改Change，因此最终您将不会得到正确的结果。第三，它更容易使更改为整数。要获得找零的最后两位数(便士)，您应该使用Pennies=Change mod 100，而要获得其他数字(磅)，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，你只需要把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，我会考虑简化一下。不要再除以10，再乘以10 --这对你的事业没有帮助。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可以工作，但它是一种隐式的缩小范围，可能不会像您期望的那样工作。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-给出等于或小于所提供的值的最大整数。

还要注意Change.ToString的使用-所有内部类型都是从超类型Object派生的，这意味着它们实现了方法ToString。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#"位)对其应用格式化。Have a look at the MSDNpage on the subject查看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

change值应该等于一个值，而不是一个字符串。需要将其更改为如下所示

If change < 0 Then

通常，当我控制字符串时，我会使用&运算符，因为我不太确定=+版本是否有效(我从未尝试过)

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