Here is one of your methods rewritten using Int32.TryParse. I assumed you're doing txtTotalCost.Substring(1) to trim off the currency symbol. There are probably safe ways to do this, I'm just going to trim "$" for this example.
protected void btnOrderTickets_Click(object sender, EventArgs e)
{
int numberOfTickets, ticketCost, eventId;
if(Int32.TryParse(txtNumberOfTickets.Text, out numberOfTickets) &&
Int32.TryParse(txtTotalCost.Text.TrimStart('$'), out ticketCost) &&
Int32.TryParse(txtEventID.Text, out eventId))
{
DateTime dt = Convert.ToDateTime(Session["date"]);
TicketsDataAccessDataContext NewOrder = new TicketsDataAccessDataContext();
int returnedValue = NewOrder.PlaceOrderFull(eventId, txtEventDescription.Text, dt, Session["State"].ToString(), Session["section"].ToString(), Session["Row"].ToString(), numberOfTickets, ticketCost, "vfateev");
if (returnedValue != 0)
{
lblOutput.Text = "Error has occured. Please try again";
lblOutput.Visible = true;
btnOrderTickets.Visible = false;
}
else
{
lblOutput.Visible = true;
lblOutput.Text = "Thank you";
btnOrderTickets.Visible = false;
}
}
else
{
lblOutput.Visible = true;
lblOutput.Text = "Some validation error message here...";
}
}
You will need to make similar modifications to txtNumberOfTickets_TextChanged1
to ensure the user has entered valid text.