Binaryworld - Test for Leap Year ... [ VB -> Date-Time ]

As long as you trust VB's IsDate function (and you can, trust me), here's the shorted and fastest method to check if a year is a leap year or not:

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Function IsLeapYear(year As Integer) As Boolean
IsLeapYear = IsDate("2/29/" & CStr(year))
End Function

Here's is another quick method, based on the DateSerial function

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IsLeapYear = DateSerial(year, 2, 29) <> DateSerial(year, 3, 1)

UPDATE: Mathias Schiffer from Germany sent us the "regular" code that lets you get to the same result without relying on the IsDate function. This is based on the definition of leap year, that is: a leap year must be divisible by 4 (without any remainder), and century years (eg 1800, 1900, 2000, ...) are leap years only if they're exactly divisble by 400. For example, 1900 wasn't a leap year, while 2000 is.
Function IsLeapYear(year As Integer) As Boolean
IsLeapYear= (year Mod 4 = 0 And (year Mod 100 <> 0 Or year Mod 400 = 0))
End Function

UPDATE: Monte Hansen from Austria has pointed out that year 3600 is not a leap year. This correction has been proposed to account for the slowing of the Earth's spinning on it's axis and its slowing of its orbit around the sun - and to bring the seasonal, siderial and lunar years into synch again). So, the above function should be rewritten as:

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Function IsLeapYear(year As Integer) As Boolean
IsLeapYear= (year Mod 4 = 0 And (year Mod 100 <> 0 Or year Mod 400 = 0) And _
year <> 3600)
End Function

For most practical reasons this correction is useless, but it's surely an interesting point. Interestingly, though, the DateSerial function reports that year 3600 is a leap year, so it seems that - after all - you can't completely trust VB!