function get_day($date) {
    $tem = explode('-' , $date); //切割日期 得到年份和月份
    $year = $tem['0'];
    $month = $tem['1'];
    if( in_array($month , [1,3,5,7,8,10,12])){
      $text = '31';// $text = $year.'年的'.$month.'月有31天';
    }elseif( $month == 2 ){
    	//判断是否是闰年
      	if ( $year%400 == 0 || ($year%4 == 0 && $year%100 !== 0) ){
        	$text = '29';// $text = $year.'年的'.$month.'月有29天';
      	}else{
        	$text = '28';// $text = $year.'年的'.$month.'月有28天';
      	}
    }else{
      $text = '30'; // $text = $year.'年的'.$month.'月有30天';
    }
    return $text;
}
echo get_day("2024-05-28");
//输出 31