How the Number of days can be calculated between two strings in PHP?

`$flyingdate = date('Y-m-d H:i:s');
$task_end_date = '2023-05-15'; 
$delays = ($flyingdate - $task_end_date);`

Problem is that, String variables can not no be changed,
I tried with date difference and string comparison function but useless
It can not tell the exact difference of days i.e. actually telling delays of days from flying to task end date,
I want difference in term of days(store in $delays) and also condition should be
delays set to zero , if days are negative;

Hi Hafiz i hope you are doing well, as i can see that when you declare $task_end_date variable you declared it as a string and $flyingdate you use date class what i recommend is to use date class in both variables, so you can calculate the difference in days between two dates there is the code i recommend you to use :

$flyingdate = new DateTime();
$task_end_date = new DateTime('2023-05-15');

// To calculate the difference between the dates
$interval = $flyingdate->diff($task_end_date);

// Change the difference to days format
$delays = $interval->format('%r%a');

// Check if the difference is negative
if ($delays < 0) {
    $delays = 0;
}

// Display the delays
echo "Delays: $delays days";

As you can see in this code,we have DateTime objects for the flying date and the task end date. Then, we calculate the difference between the two dates using the diff() method. We use the %r%a format to get the signed difference in days, then we use a condition that check if the date difference in negative.
have a good day sir .

You can do like this, time() returns the current timestamp, strtotime also returns timestamp, so substracting both and converting the seconds to days

$flyingdate = time();
$task_end_date = strtotime('2023-05-15');
$delays = $flyingdate - $task_end_date;

$days_diff = $delays / (60 * 60 * 24);
$rounded_days_diff = (int)floor($days_diff);

It worked, thanks
but now, the problem is that I am working in PHP with a database on localhost, each time my $flyingdate and $delays are updated,
I want it to update only one time. I want this if condition to run once when $status == 100 and some condition that show do not enter in loop, I tried with empty $flyingdate, but it become empty every time I run the code, I want some condition that it will always work one time, as in below code,

  if(($status == 100) && (empty($flyingdate))){
        $flyingdate = date('Y-m-d H:i:s');
        $flyingtime = time();
        $task_end_date = strtotime($last_end_date);
        $delays1 = $flyingtime - $task_end_date;
        $days_diff = $delays1 / (60 * 60 * 24);
        $delays = (int)floor($days_diff);
    }