Procedure RETURNING_A_BOOK
{  
   while (CANCEL button not pressed)
   {  
     if(OK button pressed)
     {
       read in Call_Number from the text-box;
       checks for syntax error on Call_Number;

       if(syntax error on Call_Number occurred)
         display error message(syntax error occurred);

       else /* no syntax error */
       {
         if(Call_Number doesn't exist in database)
            display error message(call number doesn't exist);

         else if(Circulation_Status is On_Loan or On_Hold or Overdue)
         {
           update Circulation_Status as Available in database;
           display message(book successfully returned);

           if(Circulation_Status is On_Hold)
           {
             open new pop-up window displaying a holder's information;

             if(PRINT button pressed) 
               print out the holder's information;

             else /* CLOSE button */ 
               close current window;

             update Circulation_Status as On_Loan in database;
             update Loans.User_ID as a holder and Loans.Loan_Date as today for book copy with Call_Number in database;
           }
         }

         else /* Circulation_Status is Available or Out_of_Circulation */
           display error message(The book is not on loan);
       }
     }
     else if(CLEAR button pressed) 
   clear the contents in the entry field;

     else /* HLEP button */
     {
       open new pop-up window displaying help;

       if(CLOSE button pressed) 
         close help window;
     }
   }
}