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Re: odd or even day?
by saintmike (Vicar) on Jan 07, 2006 at 17:45 UTC
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Dividing an integer by 24 and then muliplying it by 60*60 is equivalent to multiplying it by 150 -- which will always result in an even number.
But there's also a problem with your date math: Assuming that you want to know if the day of the month is odd or even, use Perl's localtime function or, for advanced functionality, DateTime. Unless you want to deal with leap years, months with 28, 30, 31 days etc yourself. | [reply] |
Re: odd or even day?
by Not_a_Number (Prior) on Jan 07, 2006 at 19:52 UTC
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Not quite sure what you mean by 'odd' and 'even'.
January 7 2006 is the 13,155th day since the start of the epoch. It is therefore 'odd' by your calculation (update: I should have written something like "by your calculation adjusted as per replies above"). However, January 7 2007 will be the 13,520th day, and therefore 'even'.
If that is what you want, fine, just ignore this post.
However, for a more normal definition of 'odd/even' - ie Jan 7 is odd, Jan 8 is even, Feb 1 is odd, Feb 2 is even, etc - you could do:
print +( localtime )[3] % 2 ? "odd\n" : "even\n";
Or else, counting from the beginning of the year - ie March 1 is the 60th day (even) in a normal year, but the 61st day (odd) in a leap year:
print +( localtime )[7] % 2 ? "even\n" : "odd\n";
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Re: odd or even day?
by McDarren (Abbot) on Jan 07, 2006 at 17:47 UTC
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#!/usr/bin/perl -w
use strict;
my $var=time/(24*60*60);
print $var%2 ? "odd\n" : "even\n";
The only difference is the parentheses. I'm not sure why they are required. Perhaps somebody else can explain that... | [reply]
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* and / have the same precedence and evaluate left to right so time/24*60*60 is equivelent to (time/24)*60*60, which is not what OP intended.
Update: See perlop Operator Precedence and Associativity.
DWIM is Perl's answer to Gödel
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The only difference is the parentheses. I'm not sure why they are required. Perhaps somebody else can explain that...
I think its because perl follows standard mathematical operator precedence rules: B.E.D.M.A.S (Brackets, exponents, division, multiplication, addition, subtraction.)
update: Grandfather's explanation is better.
---
$world=~s/war/peace/g
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Thanks for the replies. I'd completely forgotten about precedence rules, seems to have sorted it out.
Thanks alot
Jon
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Re: odd or even day?
by trammell (Priest) on Jan 07, 2006 at 17:39 UTC
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Check your math. You can use paper and pencil to estimate the current day number according to your scheme, then print $var and see if it's in the right ballpark.
Update: quick sanity check: assume there are 365 days in each year. This is 2006, so there have been about 36 * 365 days:
36 * 365 ~ 10 * 36 * 36
= 10 * 12 * 12 * 9
~ 14400
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This was the reason why I'm using UNIX time to avoid issues such as this. I'm assuming that 'time' provides this, is that correct, I believe so
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Re: odd or even day?
by Anonymous Monk on Jan 07, 2006 at 17:47 UTC
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$var=time/24/60/60;
print $var%2 ? "odd\n" : "even\n";
...or...
$var=time/(24*60*60);
print $var%2 ? "odd\n" : "even\n";
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Re: odd or even day?
by ysth (Canon) on Jan 08, 2006 at 03:16 UTC
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Your problems seem to have been straightened out, so I'm going to suggest looking at the odd or even test on ambrus's homenode. | [reply] |
Re: odd or even day?
by ambrus (Abbot) on Jan 08, 2006 at 15:21 UTC
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Take care with this because time/(24*60*60)%2 needn't switch at midnight, but some other time of the day.
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