Hi Sivamba,
Dearness Allowance is an allowance which is paid for what u can say Mahangai Bhatta. Generally It is 20 to 40 % of Gross pay. It is neccessary to include it in Salary Structure. Some Company includes it with basic
Basic 5000
DA 3000
Basic+DA 8000
but it should be in structure.
Gratuity is a award given by employer for the completness of five regular service year. But for claiming gratuity you have to complete five years regular service in same organisation.
Formula for calculating gratuity is
(Last drawn salary/26*15)*No. of completed service
If you have still any doubt feel free to write me on

Regards,
Sanjeev