Include error on php 4.3.2

[dlc2000]

Warning: main(.php): failed to open stream: No such file or directory in /home/xxxxx/public_html/std.php on line 52

Warning: main(): Failed opening '.php' for inclusion (include_path='.:/usr/lib/php') in /home/xxxx/public_html/std.php on line 52

this should be the line 52:

              <?

if (file_exists($inc.".htm")) {
include $inc.".htm";
} else {
include $inc.".php";
}
?>

[Brak]

Looks like $inc is null, it's trying to open a file called ".php", meaning there was no value for $inc.