Hi Santosh,
After getting date, month and year values from user. Do proper validation like,
date - check whether the number is in between 1-31. Do number validation
month - check whether the number is in between 1-12. Do number validation.
year - check length is of 4 digit, whether user entered number, check for some range like 1970-2010.
In all the above else cases alert error messages.
Dec 7, 2010