php 小知识点

<pre code_snippet_id="1793776" snippet_file_name="blog_20160729_1_9159542" name="code" class="php"><span style="font-family:SimSun;font-size:14px;">function add(){</span>

<span style="font-family:SimSun;font-size:14px;">    return 3</span>

<span style="font-family:SimSun;font-size:14px;">}$a = add(100);echo $a;</span>

"${username}"

<?php$var = "hello";$var_ = "world";echo "{$var}_ $var_";