Hooray, it’s that magical day that only comes every four years! And guess what, a bunch of date-dependent code just broke because someone didn’t account for this special day.
In a project that I’m working on, there’s some validation code that goes like this:
var thirteenYearsAgo = new DateTime(DateTime.Now.Year - 13, DateTime.Now.Month, DateTime.Now.Day);
This code is used to validate birthdate and whether we have to treat the user as a child. You should already see the problem: 13 years ago, there was no 2/29. Instead, you should favor the following (which is also much simpler to read):
var thirteenYearsAgo = DateTime.Today.AddYears(-13);