确定数组中有多少连续字段为空

Question

I have an array with variables like:
$shippingtimearr = array("", "1630", "1530", "1530", "1530", "", "");

Each field in this array represents a weekday.
I need to determine how many consecutive fields are empty depending on the day ("starting field").

For example:
If the start is $shippingtimearr[5] it should return 3 since next "Monday" ($shippingtimearr[0]) is NULL.
If the start is an array value that is not NULL, it should return 0;

I tried creating a "for" loop like this:

for( $i = 2; $shippingtimearr[$i] = 0; $i++ ) {
            $counter++;
         }

But it didn't work and obviously, this would not account for the fact that a "week" should be looped again to see if the first days next week are "NULL".

Answer 1

Since nobody seemed to understand exactly what I was looking for, I will post a solution I came up with myself using a "while" loop:

$counter = 0;
$shippingtimearr = ["", "1630", "1530", "1530", "1530", "", ""];
$start = 3;

while ($shippingtimearr[$start++] == NULL) {
    ++$counter;
    if ($start > 6) $start = 0;
}