Use the User Input Critia as part of Query! (Mysql)

Dear all I had a form which ask user to input the Staff Number to be as part of the query, but when i execute it, it seems not working at all here is what i wrote in php The user input box is : $StaffNum $query="select name,department,Leave_From,Leave_To,Leave_Total,Reason from leaverequest where Staff_Number="<?print("$StaffNum");?>" and authorized is null"; But said there is error on this line, which is what i expected!! So could anyone pls tell me how i can get the varaible into part of the Query of Mysql? Thx jack jack@nedcor.com