HELP To Write Stored Procedure Whose Values Are Calculated Automatically In Database

 Hi frdz,
    I m creating my web-application in asp.net with C# 2005 and using sql server 2005.
    I have created the stored procedure for the insert,update.
    I want to know how to write the mathematical calculations in the stored procedure..
    Pls tell me from the below  stored procedure  were i m making the mistake  ??
    As the discount and the total amount are not calculated by itself....and stored in the database
   How to convert the @discpercent numeric(5,2) to@discpercent ="NoDiscount" should be displayed when no discount is being given to the customers....

 
  ALTER PROCEDURE CalculationStoredProcedure

@accountid int output,
@accountname varchar(20),
@opbal numeric(10, 2),
@opbalcode char(2),
@total numeric(10, 2),
@clbal numeric(10, 2),
@clbalcode char(2),
@discpercent numeric(5,2),
@discamt numeric(10, 2)


as


begin
set nocount on



if @opbal IS NULL OR @opbal = 0

begin
select @opbal=0
select @opbalcode= ' '
select @clbal= 0
select @total= 0
select @clbalcode= ' '
@discpercent ="NoDiscount"
@discamt=0
end




select @accountid = isnull(max(accountid),0) + 1 from accountmaster



select @total=@opbal - @clbal from accountmaster
select @discamt=@total* @discpercent/100 from accountmaster

begin
insert into accountmaster
(
accountname,opbal,opbalcode,clbal,clbalcode

)
values
(
@accountname,@opbal,@opbalcode,@clbal,@clbalcode
)

end

set nocount off
end

 
 
  


Thanxs in adv...