The answer is very simple: it is the full set of all dates in the given range. Why? Because "birthday" means day-months combination; and each of them is someone's birthday. There are no days which are "not birthdays". These simple speculations should show you how important to formulate problems precisely.
And the following hints are to teach you how important to solve problems by yourself. All you need is this:
http://msdn.microsoft.com/en-us/library/xcfzdy4x.aspx[
^],
http://msdn.microsoft.com/en-us/library/system.datetime.compare.aspx[
^] (but instead, use '==', '>', '<', '>=' or '<='),
http://msdn.microsoft.com/en-us/library/system.datetime.date.aspx[
^],
http://msdn.microsoft.com/en-us/library/system.datetime.day.aspx[
^],
http://msdn.microsoft.com/en-us/library/system.datetime.month.aspx[
^].
The key hint: you need to ignore time and year part of the time. Also, you will need to resolve the problem: what to do if the given range has dates of more then one year.
—SA
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