PHP format date in a dropdown not working - php

Question

Im a bit stumped as i have some code to generate a simple dropdown of date for 21 days in advance.
It works fine as such however the output is not showing the right date instead its showing 1st Jan 1970
$timestamp = strtotime('today');
$output = [];
for ($day = 0; $day < 21; $day++) {
$output[] = date('d M y', strtotime(sprintf('+%d days', $day), $timestamp));
}
echo "<select name='days'>";
foreach ($output as $day)
{
echo "<option value='".$day."'>".date('l jS \of F Y',$day)."</option>";
}
echo "</select>";
if i echo just $day as the outpout value it displays in the DD/MM/YYYY format but i want it to display Day Name Date of Month Year
so whats not correct with using
date('l jS \of F Y',$day)
Im sure its something dumb but ive checked over all the various posts around on date but i cant for the life of me figure this out.

Answer 1

The function date() takes as its second argument a time in seconds.

Answer 2

If you look at the PHP:date documentation, you'll find that the second argument expects an integer, not a string.
Change your code to the following:
<?php
$output = [];
for ($day = 0; $day < 21; $day++) {
$output[] = strtotime(sprintf('+%d days', $day));
}
echo "<select name='days'>";
foreach ($output as $day)
{
echo "<option value='".$day."'>".date('l jS \of F Y', $day)."</option>";
}
echo "</select>";
Rather than filling your output array with strings, you'll see here that we instead fill it with 21 timestamps.
Once you begin looping through your output array, passing in the timestamp to the second argument of the date function will yield the output you're expecting.
I'm keeping the value of each option set to that timestamp, as it makes everything easier to work with if you need to process any POST data. But you're free to adjust the formatting there as needed.
Here's a working example that you can play around with.
Edit:
Just for funsies, here's how you can do it in a more object-oriented style. I feel it's a little more succinct this way, but it's up to you if you want to take this approach or not.
<?php
$today = new DateTime();
echo "<select name='days'>";
for ($day = 0; $day < 21; $day++)
{
echo "<option value='".$today->getTimestamp()."'>".$today->format('l jS \of F Y')."</option>";
$today->add(new DateInterval("P1D"));
}
echo "</select>";