Is this a safe practice in php?
<p>I am trying to make an online calculater where people can calculate using form in my site, people can POST in form and result is GET by url string. Is it safe ?</p>

<p>html</p>

<pre><code>&lt;form id="form1"&gt;
            &lt;input type="text" name="user_price" size=2/&gt;
            &lt;?php echo form_dropdown('selling', $rates);?&gt;
            &lt;input type="submit" value="submit"&gt;
            &lt;/form&gt;
</code></pre>

<p>php</p>

<pre><code>        &lt;?php 
        if((int)$_GET['user_price']){
        echo 'Total '. $_GET['user_price'] * $_GET['selling'];
        }else if((string)$_GET['user_price'] OR (array)$_GET['user_price']){
            echo 'enter number not characters';
        }else{
            echo '';
        }
        ?&gt;
</code></pre>
