title: how to add multiple textbox numbers, and store the sum as a double in variable
body: <p>Here is my issue. I want to be able to sum the values of 10 textbox's into a double type variable. </p>
  
  <p>The problem is that the textbox values are populated by a database and are not always filled. I want to be able to sum the values of all 10 without forcing a default value of zero in textbox's that are null.</p>
  
  <pre><code>amount = Convert.ToDouble(amount1TextBox.Text + amount2TextBox.Text + amount3TextBox.Text + amount4TextBox.Text + amount5TextBox.Text + amount6TextBox.Text + amount7TextBox.Text + amount8TextBox.Text + amount9TextBox.Text + amount10TextBox.Text);
  </code></pre>