mark php安全问题

<code><span>$a</span> = <span>'asdfgh'</span>；<span>//字符串类型的a</span><span>echo</span><span>$a</span>[<span>2</span>]；  <span>//根据php的offset 会输出'd'</span><span>echo</span><span>$a</span>[x]；  <span>//根据php的预测，这里应该是int型，那么输入string，就会被intval成为0 也就是输出'a'</span></code>

<code><span>$i</span> =<span>"2abc"</span>;
<span>switch</span> (<span>$i</span>) {
<span>case</span><span>0</span>:
<span>case</span><span>1</span>:
<span>case</span><span>2</span>:
    <span>echo</span><span>"i is less than 3 but not negative"</span>;
    <span>break</span>;
<span>case</span><span>3</span>:
    <span>echo</span><span>"i is 3"</span>;
}</code>