Something for the weekend #5: Testing for a leap year 6

[Mike Lewis]

After our excursion into American TV history, today's exercise returns to VFP programming fundamentals.

Your task is to write a function that receives a year (e.g. 2015), and returns .T. if the year is a leap year.

That's all there is to it. As usual, kudos will go to the person who suggests the smallest function (that is, the least amount of code). It doesn't have to be particularly readable or easy to understand.

The function must not have any side effects. If it changes any aspect of the environment (such as SET values), it must change it back again.

If you are one of the first to respond, please use

Spoiler

tags to hide your answer. (An easy way to insert these tags is to use the little yellow icon to the right of the

 icon at the top of the editing window.)

Mike

__________________________________
Mike Lewis (Edinburgh, Scotland)

[url=http://www.ml-consult.co.uk/foxstuff.htm]Visual FoxPro articles, tips and downloads[/url]

 

[vgulielmus]

Ha, at last I'm the first!

Spoiler

FUNCTION leapyear(tnYear as Integer)
RETURN !EMPTY(DATE(m.tnYear,2,29))

Respectfully,
Vilhelm-Ion Praisach
Resita, Romania

 

[Tore Bleken]

That's way too easy.
<spoiler>lparameters tnYear
return !isblank(date(tnYear,2,29))</spolier>

 

[Tore Bleken]

Really, is there no way to edit one of your own already submitted post?

 

[vgulielmus]

A math approach

Spoiler

FUNCTION leapyear2(tnYear as Integer)
RETURN ((m.tnYear % 4) + FLOOR(m.tnYear / 100) * (SIGN(m.tnYear % 100) - 1)) % 4 =0

Really, is there no way to edit one of your own already submitted post?

Usually (but not always) I press Preview before Submit Post...

Respectfully,
Vilhelm-Ion Praisach
Resita, Romania

 

[Tore Bleken]

Same here, but not in this case. However, I am surprised that you can't edit your own messages, at least until others have replied to it.

 

[Mike Lewis]

Oh, heck. This was obviously much too easy.

Vilhelm-Ion's first solution was the one I had in mind. His second one also works, of course, but the first one meets the size criterion. Well done to Tore for getting it as well.

I'm going to have to think of something more difficult next time. Or, better, how about one you guys setting a puzzle of your own?

Mike

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Mike Lewis (Edinburgh, Scotland)

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[Mike Lewis]

I am surprised that you can't edit your own messages, at least until others have replied to it.

Yes, that's a common feature in forums. Either you can edit before someone replies, or there is a time window - typically half an hour - during which edits are allowed. But that's never been a feature of Tek Tips.

I always make a point of using the preview whenever I use any kind of tags.

Mike



__________________________________
Mike Lewis (Edinburgh, Scotland)

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[Olaf Doschke]

Since I've already seen the solution, the empty return value from DATE(year,2,29) makes it easy to get the last february of any year as:

EVL(Date(tnYear,2,29),Date(tnYear,2,28))

Yet it's still simpler to compute

Date(tnYear,3,1)-1

And you may also test

? "leap year",Day(Date(tnYear,3,1)-1)=29

Bye, Olaf.

 

[Mike Lewis]

Thanks, Olaf. All good stuff to add to the pot.

Mike

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Mike Lewis (Edinburgh, Scotland)

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[Mike Lewis]

A quick follow-up.

Today is Friday 13th February 2015. Consider this code:

[tt]ldToday = {^2005-02-13}
? GOMONTH(ldToday, -1)[/tt]

The result is what you would expect.

Now try this:

[tt]ldToday = {^1753-02-13}
? GOMONTH(ldToday, -1)[/tt]

No surprise there either.

But then do this:

[tt]ldToday = {^1753-02-13}
ldLastMonth = GOMONTH(ldToday, -1)
? GOMONTH(ldLastMonth, -1)[/tt]

This time, you get a blank date. Why?

Mike


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Mike Lewis (Edinburgh, Scotland)

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[EzLogic]

<spoiler>
?IsLeap(2016)
FUNCTION IsLeap(tnYear)
RETURN IIF(MONTH(CTOD('02/28/'+TRANSFORM(tnYear)) + 1) = 2,.t.,.f.)
ENDFUNC
</spoiler>

Ez Logic
Michigan

 

[Tore Bleken]

Because September 14, 1752 is the first legal date in VFP. Check help for Sys(1), or read here

https://msdn.microsoft.com/en-US/LIBRARY/w438d4c4(v=vs.80).aspx

 

[Mike Lewis]

Thanks for your contribution, EZ. A couple of points:

Your solution will work, but it depends on DATE being set to American. To make it work consistently, you would have to save SET("DATE") to a variable, then SET DATE AMERICAN, then after executing the code SET DATE to what it was before.

Also, whenever you see code in this general form:

[tt]IIF(<condition>, .T., .F.)[/tt]

you can always shorten it to:

[tt]<condition>[/tt]

Mike

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Mike Lewis (Edinburgh, Scotland)

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[EzLogic]

Mike, Correct, i just simply slapped it together. To add to your observation, which is very good, I didn't even do a try catch either. Example, someone passed a negative year? or someone passed a year that is 4646464756, or a blank year? (maybe from a date field in the table, which is empty or null) etc..

I am sure it can get more refined, i just wanted to show a simple way (before too many elaboration on the function) on one of the ways that one can test for leap year.

Ez Logic
Michigan

 

[Tore Bleken]

Regarding the accuracy for year 1752, read more here:

http://flylib.com/books/en/1.18.1.803/1/

 

[TamarGranor]

Without reading anyone else's answer:

Spoiler

FUNCTION IsLeapYear(dDate)

RETURN EMPTY(DATE(YEAR(m.dDate), 2, 29))

 

[TamarGranor]

And I see a couple of bugs already in my code. Take 2:

Spoiler

FUNCTION IsLeapYear(nYear)

RETURN NOT EMPTY(DATE(m.nYear, 2, 29))

 

[TamarGranor]

On the 1752 question, the key issue is that 1752 is when the British empire adopted the Gregorian calendar.

Given that it's Presidents' Weekend here in the US, highly appropriate question because we (at least those of us of a certain age) were all taught that Washington's birthday is February 22, but in fact, he was born on February 11, 1732. When the Gregorian calendar was adopted in 1752, his birthday moved to February 22.

Tamar

 

[Mike Lewis]

Since several of you have posted the correct answer, I'll dispense with the spoilers. This is the one I had in mind:

[tt]FUNCTION IsLeapYear(nYear)
RETURN NOT EMPTY(DATE(m.nYear, 2, 29))[/tt]

Keeping in mind that I asked for the smallest function - not necessarily the most readable - we can make a small improvement:

[tt]FUNC IsLeapYear(nYear)
RETU ! EMPT(DATE(m.nYear, 2, 29))[/tt]

Personally, I hate abbreviating code in that way. I almost never use four-letter abbreviations for keywords, and I prefer to use NOT rather than !, because it is more readable. But I did ask for the smallest possible code.

So thank you for your replies. I hope you all found the exercise interesting.

Mike




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Mike Lewis (Edinburgh, Scotland)

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