There's always more than one way to do it .. I like to switch things around and test for the least likely outcome first .. check to see if the year is divisible by 400, then 100, and finally 4. I think it also makes the code a little more transparent, but everyone's got their own style ..
#!/usr/bin/perl
use strict;
use warnings;
my %testData = (
1900 => 0,
1904 => 1,
1972 => 1,
1973 => 0,
1999 => 0,
2000 => 1,
2001 => 0,
2004 => 1
);
{
foreach my $this ( keys %testData ) {
if ( $testData{$this} == leapYear($this) ) {
print "Correct - $this year "
. ( $testData{$this} ? "is" : "is not" )
. " a leap year.\n";
}
else {
print "Error with $this entry ..\n";
}
}
}
sub leapYear {
my $year = shift;
if ( $year % 400 ) {
if ( $year % 100 ) {
# 3. Simple case: it's a leap year if it's divisible by 4
return ( $year % 4 ) ? 0 : 1;
}
else {
# 2. If it's divisible by 100: it's not a leap year.
return 0;
}
}
else {
# 1. If it's divisible by 400: it's a leap year.
return 1;
}
}
I've numbered the comments to make it a little clearer which result might be returned first, although this could be made even clearer by reversing the meaning of the conditionals so that the routine looks like this:
sub leapYear {
my $year = shift;
if ( $year % 400 == 0 ) {
# 1. If it's divisible by 400: it's a leap year.
return 1;
}
else {
if ( $year % 100 == 0 ) {
# 2. If it's divisible by 100: it's not a leap year.
return 0;
}
else {
# 3. Simple case: it's a leap year if it's divisible by 4
return ( $year % 4 ) ? 0 : 1;
}
}
}
Alex / talexb / Toronto
Thanks PJ. We owe you so much. Groklaw -- RIP -- 2003 to 2013.