如何获取一年的所有周？

代码如下

<?php
function get_week($year="")
{
    if($year===""){$year=date("Y");}
    $year_start = $year . "-01-01";
    $year_end = $year . "-12-31";
    $startday = strtotime($year_start);
    if (intval(date('N', $startday)) != '1')
    {
        $startday=strtotime("last monday",strtotime($year_start));
        //获取年第一周的日期
    }
    $year_mondy = date("Y-m-d", $startday);//获取年第一周的日期
    $endday = strtotime($year_end);
    if (intval(date('W', $endday)) == '7')
    {
        $endday=strtotime("last sunday",strtotime($year_end));
    }
    $num = intval(date('W', $endday));
    for ($i = 1; $i <= $num; $i++)
    {
        $j = $i -1;
        $start_date = date("Y-m-d", strtotime("$year_mondy $j week "));
        $end_day = date("Y-m-d", strtotime("$start_date +6 day"));
        $week_array[$i] = array($start_date,$end_day);
    }
    return $week_array;
}
?>

 调用后结果如下：

获取一年的所有周_i++