calculation is only performed once on food ordering form (VB) - vb.net

Question

I am making a food ordering form, and I am having trouble with the calculations. Every time a hotdog is ordered the form is supposed to add the cost to the total amount, so one hotdog is 2 dollars, add another and it says 4 dollars, etc. But it only performs the calculation once, so no matter how many items I add to the order the price stays the same, as if I had only ordered one.
I don't get any errors at runtime so it must be a logical error. Here is the full code. I don't know what other information I should give at this moment. All help is appreciated.
Public Class DroneDogs
Dim DogChoice As String
Dim condiment1 As String
Dim condiment2 As String
Dim condiment3 As String
Const DBL_TAX_RATE As Double = 0.07
Const DBL_DRONE_DOG As Double = 1.99
Dim intNumDog As Integer
Dim dblSubTotal As Double
Dim dblSalesTax As Double
Dim dblTotalCost As Double
Private Sub btnAddCustomer_Click(sender As Object, e As EventArgs) Handles btnAddCustomer.Click
cboCurrentCustomers.Items.Add(txtAddCustomer.Text)
End Sub
Private Sub optBeef_CheckedChanged(sender As Object, e As EventArgs) Handles optBeef.CheckedChanged
If (optBeef.Checked) Then
DogChoice = "Beef Dog"
End If
End Sub
Private Sub optPork_CheckedChanged(sender As Object, e As EventArgs) Handles optPork.CheckedChanged
If (optPork.Checked) Then
DogChoice = "Pork Dog"
End If
End Sub
Private Sub optTurkey_CheckedChanged(sender As Object, e As EventArgs) Handles optTurkey.CheckedChanged
If (optTurkey.Checked) Then
DogChoice = "Turkey Dog"
End If
End Sub
Private Sub chkKetchup_CheckedChanged(sender As Object, e As EventArgs) Handles chkKetchup.CheckedChanged
If (chkKetchup.Checked) Then
condiment1 = " + Ketchup"
Else
condiment1 = Nothing
End If
End Sub
Private Sub chkMustard_CheckedChanged(sender As Object, e As EventArgs) Handles chkMustard.CheckedChanged
If (chkMustard.Checked) Then
condiment2 = " + Mustard"
Else
condiment2 = Nothing
End If
End Sub
Private Sub chkRelish_CheckedChanged(sender As Object, e As EventArgs) Handles chkRelish.CheckedChanged
If (chkRelish.Checked) Then
condiment3 = " + Relish"
Else
condiment3 = Nothing
End If
End Sub
Private Sub btnAddDog_Click(sender As Object, e As EventArgs) Handles btnAddDog.Click
intNumDog = +1
dblSubTotal = intNumDog * DBL_DRONE_DOG
dblSalesTax = dblSubTotal * DBL_TAX_RATE
dblTotalCost = dblSubTotal + dblSalesTax
txtSub.Text = dblSubTotal.ToString("c2")
txtTax.Text = dblSalesTax.ToString("c2")
txtTotal.Text = dblTotalCost.ToString("c2")
Dim addCondiment As String = condiment1 + condiment2 + condiment3
If (DogChoice = "Beef Dog") Or
(DogChoice = "Pork Dog") Or
(DogChoice = "Turkey Dog") Then
lstOrder.Items.Add(DogChoice + addCondiment + ": " + txtTotal.Text)
Else
MsgBox("Please select a Hot Dog type.")
End If
End Sub
Private Sub btnClearOrder_Click(sender As Object, e As EventArgs) Handles btnClearOrder.Click
lstOrder.Items.Clear()
txtSub.Clear()
txtTax.Clear()
txtTotal.Clear()
chkKetchup.Checked = 0
chkMustard.Checked = 0
chkRelish.Checked = 0
optBeef.Checked = 0
optPork.Checked = 0
optTurkey.Checked = 0
End Sub
Private Sub btnExit_Click(sender As Object, e As EventArgs) Handles btnExit.Click
'Exits the program
If MessageBox.Show("Do you want to exit the DroneDogs application?", "DroneDogs",
MessageBoxButtons.YesNo, MessageBoxIcon.Question) _
= DialogResult.Yes Then
Application.Exit()
End If
End Sub
Private Sub btnOrderComplete_Click(sender As Object, e As EventArgs) Handles btnOrderComplete.Click
Receipt.Show()
End Sub
Private Sub btnRemoveDog_Click(sender As Object, e As EventArgs) Handles btnRemoveDog.Click
lstOrder.Items.Remove(lstOrder.SelectedItem)
End Sub
End Class

Answer 1

I think the problem is with the line
intNumDog = +1
In this line, you always set intNumDog to the value of +1. This is the same as:
intNumDog = 1
You want to add one to the value of intNumDog:
intNumDog += 1