PHP code error. html code gives the value of keya keyb and keyc
<p>php code error , this code keeps on giving use of undefined constant error..please help</p>

<pre><code>&lt; ? php
$d = 1;
$a = $_POST[keya];
$b = $_ POST[keyb];
$c = $_POST[keyc];
$d = $a + $b + $c;
echo $d;
 ? &gt;
</code></pre>
