Answer 1

Do you need the code or just help?

Using if and else you should make sure to write all the possibilities:
* months with 28, 30, 31 days. (if your input is 1-31-2016, the output would be 2-1-2016).
*validate the date (e g. 31-2-2016 didn't exist)
*leap years
*last day of the year (12-31-2016 the output 1-1-2017)