Understanding a simple date calculation

[Citadel]

Using the latest version of v8:

Year1 = {1/10/(year(date())} returns D:1/10/2009
Year2 = (year(date())-1) returns N:2008
Year3 = {1/10/year(date())-1} returns D:1/10/2001
Year4 = str("1/10/"+(year(date())-1)) returns C:1/10/2008
Year5 = ctod(str("1/10/"+(year(date())-1))) returns D:1/10/2008

This all makes perfect sense except Year3. Why does it return D:1/10/2001 when I expect D:1/10/2008? It's not that I can't work around it, but if I understand why A5 does this I'll avoid duplicating the problem in the future.

Thanks
Alan

[csda1]

Re: Understanding a simple date calculation

Hi Alan,

Using the latest version of v8:

Year1 = {1/10/(year(date())} returns D:1/10/2009
Year2 = (year(date())-1) returns N:2008
Year3 = {1/10/year(date())-1} returns D:1/10/2001
Year4 = str("1/10/"+(year(date())-1)) returns C:1/10/2008
Year5 = ctod(str("1/10/"+(year(date())-1))) returns D:1/10/2008

This all makes perfect sense except Year3. Why does it return D:1/10/2001 when I expect D:1/10/2008? It's not that I can't work around it, but if I understand why A5 does this I'll avoid duplicating the problem in the future.

You can't put expressions within a date constant like {mm/dd/yyyy}, only numbers where they are supposed to be. Leaving out yyyy gives you the current year. if you want to add months or years, easiest way to do it is addmonths() and addyears() functions. Days can be simply added or subtracted after a date value, as in {01/10/2009}-3

You are also mixing numbers, dates and strings and using them for the wrong functions that don't accept those types. A5 will convert to strings in some cases, but it's a bad thing to count on. str() requires a number inside, ctod() a string that looks like a date

Look at the examples in the help file under date time conversions.

[Tom Cone Jr]

Re: Understanding a simple date calculation

Alan, I think you've written an expression Alpha can't decipher, and then the Setting for 21st century dates kicks in. Consider this:

?{1/10/year(date())-50}
= {01/10/1950}

and

?{01/01/1}
= {01/01/2001}

[G Gabriel]

Re: Understanding a simple date calculation

This all makes perfect sense except Year3. Why does it return D:1/10/2001 when I expect D:1/10/2008? It's not that I can't work around it, but if I understand why A5 does this I'll avoid duplicating the problem in the future

Alan:
Your first post.. so let me be the first to welcome you aboard.. and also the first to hand you the trophy for creative imagination..unfortunately, it does not work. I mean: the creative imagination.

Don't know how much experience you have with alpha, but to test any expression, you could go to the Interactive Window and type your expression preceded by a question mark, hit enter and you will see the result.

So let's do that:

?{1/10/year(date())} 
= {01/10/2009}

Which is what you got. And, quite logically you concluded that alpha took the year from date() and that's how you ended up with that result with the year 2009.

Not so.

Alpha completley ignored everything you wrote that you think will evaluate to the year. It all added up to nothing since it had no numerals in it.

To understand, let's try few things:

?{1/10/junk} 
= {01/10/2009}
 Same result.

?{1/10/Uncle Jody Had a cat} 
= {01/10/2009}
same result

?{1/10/Uncle Jody Had [B][COLOR="Blue"]1[/COLOR][/B] cat} 
= {01/10/200[B][COLOR="Blue"]1[/COLOR][/B]}

?{1/10/Uncle Jody Had [B][COLOR="Blue"]5[/COLOR][/B] cats} 
= {01/10/200[COLOR="Blue"][B]5[/B][/COLOR]}
'Same as:
?{1/10/5} 
= {01/10/2005}
?{1/10/05} 
= {01/10/2005}
?{1/10/2005} 
= {01/10/2005}

You get the idea?
Alpha is looking for a numeral representative of the year, everything else is ignored. When no numeral is found, it's the equivalent of blank and blank defaults to the current year.

[G Gabriel]

Re: Understanding a simple date calculation

Let's push this creative imagination a little further and push alpha's buttons:

?{1/1/Uncle Jody had 123 cats}
= {01/01/0123}
?{1/1/Uncle Jody had 1234 cats}
= {01/01/1234}
?{1/1/Uncle Jody had 12345 cats}
ERROR: Invalid date constant
?{1/1/Uncle Jody had 123 cats and 5 dogs}
= {01/01/0123}
?{1/1/Uncle Jody had 12345 cats and 5 dogs}
ERROR: Invalid date constant
?{1/1/Uncle Jody had 1,234 cats}
= {01/01/2001}
?{1/1/Uncle Jody had 12,234 cats}
= {01/01/2012}
"Can you see how alpha is deciphering the year?

?{Uncle Jody had 1 cat/1/2009}
ERROR: Invalid date constant
'Hmmmm?

?{1 cat is all you need/1/2009}
= {01/01/2009}

?{1 cat is all you need/1 dog too/2009}
= {01/01/2009}

?{1 cat is all you need/3 dogs even better/2009}
= {01/03/2009}

[Tom Cone Jr]

Re: Understanding a simple date calculation

G, I like your reasoning, but want to quibble with your conclusion. Alpha does not default to the current year. 2001 is not the current year after all. Alpha uses the database's two digit date setting to conclude that year 1 is in the 21st century. The number 1 following the ignored text is what is significant, as you indicate, but then Alpha translates 1 into 2001 not by default but by observing the database setting for 2 digit years falling between 00 and 20. Since 50 is outside the typical 2 digit range, you get 1950, not 2050, if the 1 is replaced by 50. See what I mean?

[G Gabriel]

Re: Understanding a simple date calculation

Tom:
Not sure how you get 2001:

?{1/1}
= {01/01/2009}
?{1/1/}
= {01/01/2009}
?{1/1/        }
= {01/01/2009}

In fact, one of my tricks to get the current year in a variable is to evaluate one with a blank year. It will always take the current year:

dim x as c
x="{1/1}"
?eval(x)
= {01/01/2009}
'How about it?

The reason you got 1950 not 2050 is because (as many databases do) alpha could go so far in the future.
To see what I mean:

?{1/10/year(date())-50}
= {01/10/1950}
?{1/10/year(date())-10}
= {01/10/2010}
'Hmmm?
?{1/10/year(date())-11}
= {01/10/2011}
'Hmmm again?
?{1/10/year(date())-20}
= {01/10/1920}
'Same Hmmm?
?{1/10/year(date())-21}
= {01/10/1921}
'Different Hmmm?.

[Tom Cone Jr]

Re: Understanding a simple date calculation

G, I get it per post #3 in this thread...

I thought you understood that his original question did in fact include the numeral 1 in the year position, albeit trailing a series of non-numeric characters and symbols. Year3 = {1/10/year(date())-1}
That's why he got the result he obtained, and why you get 01/01/1950 if your expression looks like this:
Year3 = {1/10/year(date())-50}

BTW, I chuckle each time someone uses the word "simple" when describing an issue involving programming or computers.... Here, the topic name cracks me up. <grin>

[G Gabriel]

Re: Understanding a simple date calculation

G, I get it per post #3 in this thread...

I thought you understood that his original question did in fact include the numeral 1 in the year position, albeit trailing a series of non-numeric characters and symbols. Year3 = {1/10/year(date())-1}
That's why he got the result he obtained, and why you get 01/01/1950 if your expression looks like this:
Year3 = {1/10/year(date())-50}

Tom:
I think you missed one of my earlier posts..
To wit:
Alpha is looking for a numeral respresentative of the year.
Year3 = {1/10/year(date())-1} does have a numeral which is 1 hence you got 2001. But if it didn't have any numeral, to alpha, it's the equivalent of leaving the year number blank and if you do alpha will default to the current year. Read posts 5&7 for illustration.

[[email protected]]

Re: Understanding a simple date calculation

While we are on that subject ...kindof... then how about time as well. Does Alpha also expect the same as there are date and time combinations in the functions as well ?

[csda1]

Re: Understanding a simple date calculation

Hi Ryland,

While we are on that subject ...kindof... then how about time as well. Does Alpha also expect the same as there are date and time combinations in the functions as well ?

There are many types, Character, Numeric, Logical, Blob, Date, Date-Time, Short Time, Pointer, as well as a few other types. Each function can only take the types it was made for.

[Citadel]

Re: Understanding a simple date calculation

Thank you all for the welcome and replies. I've been dipping in and out of the forum for a couple of years now, but just reading. The posts always seem to be so well informed, and I have a high regard for your professionalism.

I think I got the idea that functions could accept different data types because A5 usually seems to cleverly 'autoconvert' data in variables to match the expected data type.

I will have to be more careful in future.

Thanks again
Alan