How do I multiply a user's text by an array item selected from a menu? - vb.net

Question

I'm trying to write a gross pay calculator, and can't quite get the coding right to multiply the user entered number by the selected pay rate.
Everything I try based off tweaking other project's code to fit my current project just returns errors.
Private strCode(,) As String = {{“P23”, “10.5”},
{“P56”, “12.5”},
{“F45”, “14.25”},
{“F68”, “15.75”},
{“F96”, “17.65”}}
Private Sub txtHours_KeyPress(sender As Object, e As KeyPressEventArgs) Handles txtHours.KeyPress
' Accept only numbers, the period, and the Backspace key.
If (e.KeyChar < "0" OrElse e.KeyChar > "9") AndAlso e.KeyChar <> "." AndAlso e.KeyChar <> ControlChars.Back Then
e.Handled = True
End If
End Sub
Private Sub BtnCal_click(sender As Object, e As EventArgs) Handles btnCalc.Click
Const V As strCodes(,)(,)
Dim txtHours As Decimal = txtHours.text
lblGross.Text = {{txtHours.Text} * {lstCodes.SelectedIndex}}
End Sub
Whether I declare the txtHours as double, decimal, it always returns the error that it can't be converted. The bottom portion of the code is non-working, but is essentially what I need to happen with this code.

Answer 1

I would expect to see something more like:
Private Sub BtnCal_click(sender As Object, e As EventArgs) Handles btnCalc.Click
If lstCodes.SelectedIndex <> -1 Then
Dim quantity, rate As Double
If Double.TryParse(txtHours.Text, quantity) AndAlso Double.TryParse(lstCodes.SelectedItem, rate) Then
Dim price As Double = quantity * rate
lblGross.Text = price
Else
MessageBox.Show("Invalid Quantity and/or Rate!")
End If
Else
MessageBox.Show("No Rate Selected!")
End If
End Sub

Answer 2

I created a structure to hold your data. A list of the type of structure then can keep the data and a List(Of T) can be bound to a list box. The display and value members are set to the properties of the structure. When an item is selected in the list box we can get the .SelectedValue and use it in the calculation.
Public Structure PayRate
Public Property RateClass As String
Public Property PayRate As Decimal
Public Sub New(rClass As String, pRate As Decimal)
RateClass = rClass
PayRate = pRate
End Sub
End Structure
Private PayRates As New List(Of PayRate)
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
PayRates.Add(New PayRate(“P56”, 12.5D))
PayRates.Add(New PayRate(“F45”, 14.25D))
PayRates.Add(New PayRate(“F68”, 15.75D))
PayRates.Add(New PayRate(“F96”, 17.65D))
ListBox1.DataSource = PayRates
ListBox1.DisplayMember = "RateClass"
ListBox1.ValueMember = "PayRate"
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim Hours As Decimal
If Decimal.TryParse(TextBox1.Text, Hours) Then
Label1.Text = (Hours * CDec(ListBox1.SelectedValue)).ToString("000.00")
Else
MessageBox.Show("Please enter a valid number in Hours box.")
End If
End Sub