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copied!<p>Many years ago, to provide an <a href="http://cloud9.hedgee.com/age" rel="noreferrer">age calculator gimmick</a> on my website, I wrote a function to calculate age to a fraction. This is a quick port of that function to C# (from <a href="http://hedgee.svn.sourceforge.net/viewvc/hedgee/trunk/chris/ckwww/ckage.php3" rel="noreferrer">the PHP version</a>). I'm afraid I haven't been able to test the C# version, but hope you enjoy all the same!</p> <p>(Admittedly this is a bit gimmicky for the purposes of showing user profiles on Stack Overflow, but maybe readers will find some use for it. :-))</p> <pre><code>double AgeDiff(DateTime date1, DateTime date2) { double years = date2.Year - date1.Year; /* * If date2 and date1 + round(date2 - date1) are on different sides * of 29 February, then our partial year is considered to have 366 * days total, otherwise it's 365. Note that 59 is the day number * of 29 Feb. */ double fraction = 365 + (DateTime.IsLeapYear(date2.Year) && date2.DayOfYear >= 59 && (date1.DayOfYear < 59 || date1.DayOfYear > date2.DayOfYear) ? 1 : 0); /* * The only really nontrivial case is if date1 is in a leap year, * and date2 is not. So let's handle the others first. */ if (DateTime.IsLeapYear(date2.Year) == DateTime.IsLeapYear(date1.Year)) return years + (date2.DayOfYear - date1.DayOfYear) / fraction; /* * If date2 is in a leap year, but date1 is not and is March or * beyond, shift up by a day. */ if (DateTime.IsLeapYear(date2.Year)) { return years + (date2.DayOfYear - date1.DayOfYear - (date1.DayOfYear >= 59 ? 1 : 0)) / fraction; } /* * If date1 is not on 29 February, shift down date1 by a day if * March or later. Proceed normally. */ if (date1.DayOfYear != 59) { return years + (date2.DayOfYear - date1.DayOfYear + (date1.DayOfYear > 59 ? 1 : 0)) / fraction; } /* * Okay, here date1 is on 29 February, and date2 is not on a leap * year. What to do now? On 28 Feb in date2's year, the ``age'' * should be just shy of a whole number, and on 1 Mar should be * just over. Perhaps the easiest way is to a point halfway * between those two: 58.5. */ return years + (date2.DayOfYear - 58.5) / fraction; } </code></pre>

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