title: "FormatException was unhandled by user code" Input string was not in a correct format
body: <p>When I click submit button without typing a <code>number in my text box</code>,</p>
  
  <p>I get error message </p>
  
  <blockquote>
    <p>FormatException was unhandled by user code, Input string was not in a
    correct format.</p>
  </blockquote>
  
  <p>Here is my code:</p>
  
  <pre><code>protected void btnSubmit_Click(object sender, EventArgs e)
  {
      int section = Convert.ToInt32(lstSectionNumber.SelectedValue);
      double ticketQuantity = Convert.ToInt32(txtNumberOfTickets.Text);
  }
  </code></pre>
  
  <p>I understand that I can validate the text box so I have to type in the number, but can anyone guide me to the correct way of fixing this? </p>
  
  <p>Thank you, I've only been using C# for a week.</p>