无法实现新赋予的值到 subtotaldecimal里面
Public Class Form1
Const Primerib_Rate_Price As Decimal = 25.95
Const Chicken_Rate_Price As Decimal = 18.95
Const Pasta_Rate_Price As Decimal = 12.95
Const Openbar_Rate_Price As Decimal = 25.0
Const Winewithdinner_Rate_price As Decimal = 8.0
Const Tax_Rate As Decimal = 0.09

Private Sub ButtonCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ButtonCalculate.Click



Dim numberoforderAmount As Integer
Dim pricedecimal, foodpricedecimal, totalpricedecimal, subtotaldecimal ,itemamountdecimal As Decimal
Dim drinkpricedecimal As Decimal = 0.0
Dim taxdecimal As Decimal = 0.0

If RadioButtonPrimeRib.Checked = True Then
pricedecimal = Pasta_Rate_Price
ElseIf RadioButtonChicken.Checked = True Then
pricedecimal = Chicken_Rate_Price
ElseIf RadioButtonPasta.Checked = True Then
pricedecimal = Pasta_Rate_Price
End If



If CheckBoxOpenBar.Checked = True And CheckBoxWinewithDinner.Checked = False Then
drinkpricedecimal = Openbar_Rate_Price
End If
If CheckBoxOpenBar.Checked = False And CheckBoxWinewithDinner.Checked = True Then
drinkpricedecimal = Winewithdinner_Rate_price
End If
If CheckBoxOpenBar.Checked = True And CheckBoxWinewithDinner.Checked = True Then
drinkpricedecimal = Openbar_Rate_Price + Winewithdinner_Rate_price
End If

Try

numberoforderAmount = Integer.Parse(TextbookNumberofOrder.Text)
itemamountdecimal = pricedecimal * numberoforderAmount + drinkpricedecimal


subtotaldecimal += itemamountdecimal
taxdecimal = itemamountdecimal * Tax_Rate
totalpricedecimal = subtotaldecimal * 1.09

LabelItemamount.Text = itemamountdecimal.ToString("N")
LabelSubtotal.Text = subtotaldecimal.ToString("N")
LabelTax.Text = Tax_Rate.ToString("C")
LabelTotalDue.Text = totalpricedecimal.ToString("N")


Catch ex As Exception

End Try
End Sub
End Class



程序是让结算价格，之后可以多次添加结算的消费价格。
但是无法将之前的数据存储下来，不知道哪一个数据写错了，希望大家帮忙
[解决办法]
Dim pricedecimal, foodpricedecimal, totalpricedecimal, subtotaldecimal ,itemamountdecimal As Decimal
把上面的变量设成类成员变量（即全局变量，放在窗体类里定义，不要放在click事件里定义)
[解决办法]

        If RadioButtonPrimeRib.Checked = True Then
            pricedecimal = Pasta_Rate_Price
        ElseIf RadioButtonChicken.Checked = True Then
            pricedecimal = Chicken_Rate_Price
        ElseIf RadioButtonPasta.Checked = True Then
            pricedecimal = Pasta_Rate_Price
        End If

        If RadioButtonPrimeRib.Checked = True Then
            pricedecimal = Pasta_Rate_Price
        ElseIf RadioButtonChicken.Checked = True Then
            pricedecimal = Chicken_Rate_Price
        ElseIf RadioButtonPasta.Checked = True Then
            pricedecimal = Pasta_Rate_Price
        End If