为什么获胜'；t这个数组的第一个元素显示在php中 - Why won't the first element of this array show in php?

Why won't the first element of this array show in php?

我有一个数组，其中包含一年中的月份，带有switch语句和while循环，但它不会显示数组的第一个元素，即一月。有人能帮我解决这个问题吗？

$calendar = array (January, February, March, April, May, June, July, August, September, October, November, December);
while($e < sizeof($calendar)) {
$k++;
$days = 30;
$days2 = 31;
switch ($calendar[$e]) {
    case  $calendar[0]:
    echo "Month ",$k,": $calendar[$e] has $days days <br>";
    break;
    case  $calendar[1]:
    echo "Month $k: $calendar[$e] has 28 or 29 days <br>";
    break;
    case  $calendar[2]:
    echo "Month $k: $calendar[$e] has $days2 days <br>";
    break;
    case  $calendar[3]:
    echo "Month $k: $calendar[$e] has $days days <br>";
    break;
    case  $calendar[4]:
    echo "Month $k: $calendar[$e] has $days days <br>";
    break;
    case  $calendar[5]:
    echo "Month $k: $calendar[$e] has $days days <br>";
    break;
    case  $calendar[6]:
    echo "Month $k: $calendar[$e] has $days2 days <br>";
    break;
    case  $calendar[7]:
    echo "Month $k: $calendar[$e] has $days days <br>";
    break;
    case  $calendar[8]:
    echo "Month $k: $calendar[$e] has $days days <br>";
    break;
    case  $calendar[9]:
    echo "Month $k: $calendar[$e] has $days2 days <br>";
    break;
    case  $calendar[10]:
    echo "Month $k: $calendar[$e] has $days days <br>";
    break;
    case  $calendar[11]:
    echo "Month $k: $calendar[$e] has $days2 days <br>";
    break;
    }
    $e++;
}

正如评论中所提到的，在使用$e之前，您没有定义它。正如您所看到的，它会产生不可预测的结果。设置它可以按预期工作。

看看它在行动中。

如果您不介意，请使用日历函数cal_days_in_month():

$year = 2013
$arr_month_name = cal_info(0)['months'];
for ($month=1; $month < 12; $month+=1) {
    $days = cal_days_in_month(CAL_GREGORIAN, $month, $year);
    echo "Month $month: $arr_month_name[$month] has $days days <br/>";
}