title: string.Format "C" (currency) is returning the string "C" instead of formatted text
body: <p>I am trying to ensure that the text in my control derived from TextBox is always formatted as currency.</p>
  
  <p>I have overridden the Text property like this.</p>
  
  <pre><code>   public override string Text
      {
          get
          {
              return base.Text;
          }
          set
          {                
              double tempDollarAmount = 0;
              string tempVal = value.Replace("$", "").Replace(",","");
              if (double.TryParse(tempVal, out tempDollarAmount))
              {
                  base.Text = string.Format("C", tempDollarAmount);
              }
              else
              {                 
                  base.Text = "$0.00";
              }                
          }
      }
  </code></pre>
  
  <p>Results:</p>
  
  <ul>
  <li>If I pass the value "Text"
  (AmountControl.Text = "Text";) , the
  text of the control on my test page
  is set to "$0.00", as expected.</li>
  <li>If I pass the value 7
  (AmountControl.Text = "7";) , I
  expect to see "$7.00", but the text
  of the control on my test page is set
  to "C".</li>
  </ul>
  
  <p>I assume that I am missing something very simple here. Is it something about the property? Or am I using the string format method incorrectly?</p>