閏年かどうかを判定する ref: http://qiita.com/items/2012

file0.php

<?php

// まじめに計算する方法
function isLeapYear($year)
{
    return ( ( $year % 4 === 0 and $year % 100 !== 0 ) or $year % 400 === 0 );
}

$years = range(2000, 2012);

foreach ( $years as $year ) {
    echo $year, ' ', var_export(isLeapYear($year), true), PHP_EOL;
}

// 2月29日があるかを判定する方法
function isLeapYear2($year)
{
    return checkdate(2, 29, $year);
}

$years = range(2000, 2012);

foreach ( $years as $year ) {
    echo $year, ' ', var_export(isLeapYear2($year), true), PHP_EOL;
}