php first week number every month - php

Question

Don,t think I can find this answer in this forum.
How to get the first week number in every month where month start by Monday. This month first week is 36 how to get that? Having this code. But don't work.
//get first week number in month
$month = 9;
$year = 2018;
$day = 1;
$firstday = new DateTime("$year-$month-1");
$dow = (int)$firstday->format('w');
$firstday->add(new DateInterval('P' . ((8 - $dow) % 7) . 'D'));
$weeknumber = $firstday->format('W');
echo $weeknumber ;

Answer 1

I think this code will do what you want. It first creates a DateTime object for the first of the month, then it moves that date forward to make it a Monday. Finally it prints the week of the year using format('W').
Edit
Updated code to print first Monday and week number for whole year
$year = 2018;
echo "Month | First Monday | Week\n";
for ($month = 1; $month <= 12; $month++) {
$firstday = DateTime::createFromFormat('Y-n-j', "$year-$month-1");
$dow = (int)$firstday->format('w');
// update to a monday (day 1)
$firstday->add(new DateInterval('P' . ((8 - $dow) % 7) . 'D'));
echo sprintf("%5d | %s | %4d\n", $month, $firstday->format('Y-m-d'), $firstday->format('W'));
}
Output:
Month | First Monday | Week
1 | 2018-01-01 | 1
2 | 2018-02-05 | 6
3 | 2018-03-05 | 10
4 | 2018-04-02 | 14
5 | 2018-05-07 | 19
6 | 2018-06-04 | 23
7 | 2018-07-02 | 27
8 | 2018-08-06 | 32
9 | 2018-09-03 | 36
10 | 2018-10-01 | 40
11 | 2018-11-05 | 45
12 | 2018-12-03 | 49