how to modify a given input in a search form?

Hi,
I have a search application calling a form app. In the search app users enter the number of their card and i am supposed to take only the first 11 digits of this no. If its one digit more, the database doesn’t find anything and returns an error.
I have been trying to find the right way to use ‘substr()’ in the “onapplicationinit” event of the search app, but it doesn’t make any changes…
Here is the code:

" $cards = ‘SUBSTR({CARD_NO},1,11)’;
$check_table = ‘cards’; // Table name
$check_where = “cards.CARD_NO = ‘$cards’”; // Where clause

// Check for record
$check_sql = ‘SELECT *’
. ’ FROM ’ . $check_table
. ’ WHERE ’ . $check_where ;
sc_select(dataset, $check_sql);

if (false == {dataset})
{
// Error while accessing database
}
elseif ({dataset}->EOF)
{
// No record found
}
else
{
// Record found
}"

Note: It works fine when a number of 11 digits is given.
What am i doing wrong??
Thanks