title: Echo string with multiple variables
body: <p>All of the following commands work but which one is considered correct in terms of security, compatibility, speed, and other conventions? </p>
  
  <pre><code>//one
  echo "$row-&gt;first_name $row-&gt;last_name &lt;br /&gt;";
  
  //two
  echo $row-&gt;first_name . ' ' . $row-&gt;last_name .'&lt;br /&gt;';
  
  //three
  echo $row-&gt;first_name;
  echo $row-&gt;last_name;
  echo '&lt;br /&gt;';
  </code></pre>