<nav class="navbar navbar-fixed-top" role="navigation">
    <div class="container">
    <div class="navbar-header">

      <a class="navbar-brand" href="#">CREP</a>

    </div>

    <div class="collapse navbar-collapse">

    <?php
      if ( 0 == 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">NOM DE LA PERSONNE</a>
          </p>
        }
        </div>

     ?>

    </div>
  </nav>