<nav class="navbar navbar-fixed-top" role="navigation">
  <div class="container">
  <div class="navbar-header">
    <a class="navbar-brand" href="#">Titre</a>
  </div>
  <div class="collapse navbar-collapse">
  

  <?php
    if ( 1 == 1 )
      {    
        <form class="navbar-form navbar-right" role="search">
          <button type="submit" class="btn btn-default">Inscription</button>
          <button type="submit" class="btn btn-default">Connection</button>
        </form>
      }
    else
      {
        <p class="navbar-text navbar-right">Bienvenue,_
          <a href="#" class="navbar-link">enanrock</a>
        </p>
      }
      </div>
   ?>
  
  </div>
</nav>