title: To set default prefix value for input field
body: <p>I have <code>form</code> which consists of 2 fields called <code>countrycode</code> and <code>Phone Number</code>.</p>
  
  <ul>
  <li>My requirement is I want add <code>+</code> as default value in country code input field. Like this:</li>
  </ul>
  
  <p><a href="https://i.stack.imgur.com/Legfq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Legfq.png" alt="enter image description here"></a></p>
  
  <ul>
  <li>And i should be able to send this prefix value(+), Along with the entered value in <code>country code</code> field.</li>
  </ul>
  
  <p>Stackblitz <strong><a href="https://stackblitz.com/edit/angular-material2-issue-vvmbnu?file=app/demo/demo.component.ts" rel="nofollow noreferrer">DEMO</a></strong></p>