Visual Studio. Adding numbers to end result - vb.net

Question

I am working on a project where there are 3 buttons. Add, subtract and exit. When I click the "Add button it should take whatever is in the current "number ordered" box and add it to the total. If I click subtract it should subract from the current total. The buttons work but I can't get the total to stay. If I put in 5, click add, then the total box states 5 but the minute I erase it, the total box erases too. Here is my code:
Option Explicit On
Option Strict On
Option Infer Off
Public Class frmMain
Private Sub btnAdd_Click(Sender As Object, e As EventArgs) Handles btnAdd.Click
Dim intNumOrdered As Integer
Dim dblTotal As Double
Integer.TryParse(txtNumOrdered.Text, intNumOrdered)
dblTotal = intNumOrdered + dblTotal
lblTotal.Text = dblTotal.ToString("C2")
End Sub
Private Sub btnSubtract_Click(Sender As Object, e As EventArgs) Handles btnSubtract.Click
Dim intNumOrdered As Integer
Dim dblTotal As Double
Integer.TryParse(txtNumOrdered.Text, intNumOrdered)
dblTotal = dblTotal - intNumOrdered
lblTotal.Text = dblTotal.ToString("C2")
End Sub
Private Sub btnExit_Click(sender As Object, e As EventArgs) Handles btnExit.Click
Me.Close()
End Sub
Private Sub txtNumOrdered_Enter(sender As Object, e As EventArgs) Handles txtNumOrdered.Enter
txtNumOrdered.SelectAll()
End Sub
Private Sub txtNumOrdered_TextChanged(sender As Object, e As EventArgs) Handles txtNumOrdered.TextChanged
lblTotal.Text = String.Empty
End Sub
End Class
What do I need to do?

Answer 1

You said:
but the minute I erase [the contents of the numordered box], the total box erases too
And your code says:
Private Sub txtNumOrdered_TextChanged(sender As Object, e As EventArgs) Handles txtNumOrdered.TextChanged
lblTotal.Text = String.Empty
End Sub
To be fair, VB's only doing exactly what you've told it to do! :)

Answer 2

There is a few things wrong here. As pointed out already you are clearing the total box. Also you are not storing the total anywhere and instead using local variables which will initialize to 0. Another thing you should check your TryParse actually succeeds before using the variable.
Public Class frmMain
Private dblTotal As Integer = 0
Private Sub btnAdd_Click(Sender As Object, e As EventArgs) Handles btnAdd.Click
Dim intNumOrdered As Integer
If Integer.TryParse(txtNumOrdered.Text, intNumOrdered) Then
dblTotal = dblTotal + intNumOrdered
lblTotal.Text = dblTotal.ToString("C2")
End If
End Sub
Private Sub btnSubtract_Click(Sender As Object, e As EventArgs) Handles btnSubtract.Click
Dim intNumOrdered As Integer
If Integer.TryParse(txtNumOrdered.Text, intNumOrdered) Then
dblTotal = dblTotal - intNumOrdered
lblTotal.Text = dblTotal.ToString("C2")
End If
End Sub
Private Sub btnExit_Click(sender As Object, e As EventArgs) Handles btnExit.Click
Me.Close()
End Sub
Private Sub txtNumOrdered_Enter(sender As Object, e As EventArgs) Handles txtNumOrdered.Enter
txtNumOrdered.SelectAll()
End Sub
Private Sub txtNumOrdered_TextChanged(sender As Object, e As EventArgs) Handles txtNumOrdered.TextChanged
lblTotal.Text = String.Empty
End Sub
End Class