Date Validation and Printing

When I enter a date, it has to be validated and the following should be printed.

1. First and the last date of the current month of the entered date.

2. First and the last date of the previous month of the entered date.

3. First and the last date of the next month of the entered date.

I am not asking for the entire program but just a clue as to how to proceed. I am a beginner and yet to learn a lot. Any help would be appreciated.

Regards,

Srinath.