Do While in php for two different dates - php

Question

Want to alert Effective Date, till it meets the condition.
Code:-
$effective_date = '2020/09/03';
$last_date = '2020/12/03';
$last_date = new DateTime($last_date);
$effective_date = new DateTime($effective_date);
do{
$edate = $effective_date->format('Y/m/d');
echo "<script>alert('".$edate."');</script>";
$nxtdate = date('Y-m-d', strtotime("+1 months", strtotime($edate)));
$effective_date = new DateTime($nxtdate);
} while($effective_date > $last_date);
It alerts only one time, but my expectation is it should be alerted 3 times

Answer 1

It alerts only one time because your while condition is not correct.
Notice that the do { ... } while (condition) loop will run at least once and continue as long as the condition is true, not until it becomes true.
Change while($effective_date > $last_date) to while($effective_date < $last_date):
$effective_date = '2020/09/03';
$last_date = '2020/12/03';
$last_date = new DateTime($last_date);
$effective_date = new DateTime($effective_date);
do{
$edate = $effective_date->format('Y/m/d');
echo "<script>alert('".$edate."');</script>";
$nxtdate = date('Y-m-d', strtotime("+1 months", strtotime($edate)));
$effective_date = new DateTime($nxtdate);
} while($effective_date < $last_date);
Ouput:
<script>alert('2020/09/03');</script><script>alert('2020/10/03');</script><script>alert('2020/11/03');</script>
Update
If you want the condition to be checked before the statements inside the loop are executed, use the while loop instead:
while ($effective_date < $last_date) {
$edate = $effective_date->format('Y/m/d');
echo "<script>alert('".$edate."');</script>";
$nxtdate = date('Y-m-d', strtotime("+1 months", strtotime($edate)));
$effective_date = new DateTime($nxtdate);
}