title: Format text box to accept only numbers and white spaces and plus sign
body: <p>I am trying to make a <code>text-box</code> which will only accept numbers, white spaces and plus sign.</p>
  
  <p>Currently I have done something like this in <code>KeyPressEvent</code> of the <code>textbox</code></p>
  
  <pre><code>if (!char.IsDigit(e.KeyChar) &amp;&amp; !char.IsControl(e.KeyChar) &amp;&amp;!char.IsWhiteSpace(e.KeyChar))
      {
                  e.Handled = true;
      }
  </code></pre>
  
  <p>I want to accept the <code>+</code> sign as well</p>
  
  <p><strong>Update</strong></p>
  
  <p>I did handle the <code>!char.IsSymbol(e.KeyChar)</code> but it will accept the <code>=</code> sign as well with the <code>+</code></p>
  
  <p>Any help!!!</p>
  
  <p>Thanks</p>