Criteria involving Lookup List of BigInt

Criteria involving Lookup List of BigInt

Hi,

I have a form (Class_Rooms)with one of the lookup fields being a  list of Students ID (BigInt).  

How does set a criteria for Class_Rooms where the list contains a particular student ID. This is what i wrote

        for each Class_Records in Class_Rooms  [List_of_Students.contains(Student.iD)]
        {

        }

But I've been getting the following error.

Error at line number : -1 
Improper Statement
Error might be due to missing ';' at end of the line or incomplete expression