How to display WordPress username?

Question

WordPress

I'm trying to display the username in the card, but the function itself is displayed.
Name output

$current_user = wp_get_current_user();
     $username = $current_user->display_name;
    echo $username;

Full code

echo '<div class="demo-card-wide mdl-card mdl-shadow--2dp">
  <div class="mdl-card__title">
    <h2 class="mdl-card__title-text">
    <?php
    $current_user = wp_get_current_user();
     $username = $current_user->display_name;
    echo $username;
?>
    </h2>
  </div>
  <div class="mdl-card__supporting-text">
  </div>
  <div class="mdl-card__actions mdl-card--border">
    <a class="mdl-button mdl-button--colored mdl-js-button mdl-js-ripple-effect" href="/account">
      Аккаунт
    </a>
  </div>   
  <div class="mdl-card__menu">
    <button class="mdl-button mdl-button--icon mdl-js-button mdl-js-ripple-effect" onclick="location.href=\'/auth/?action=logout\'">
      <i href="/?action-rcl=logout" class="material-icons">exit_to_app</i>
    </button>
  </div>
</div>';

Answer 1

$current_user = wp_get_current_user();
$username = $current_user->display_name;
echo '<div class="demo-card-wide mdl-card mdl-shadow--2dp">
  <div class="mdl-card__title">
    <h2 class="mdl-card__title-text">' . $username . '</h2>
  </div>
  <div class="mdl-card__supporting-text">
  </div>
  <div class="mdl-card__actions mdl-card--border">
    <a class="mdl-button mdl-button--colored mdl-js-button mdl-js-ripple-effect" href="/account">
      Аккаунт
    </a>
  </div>   
  <div class="mdl-card__menu">
    <button class="mdl-button mdl-button--icon mdl-js-button mdl-js-ripple-effect" onclick="location.href=\'/auth/?action=logout\'">
      <i href="/?action-rcl=logout" class="material-icons">exit_to_app</i>
    </button>
  </div>
</div>';