title: PHP - strtotime()- First Day of month problem
body: <p>I have this code</p>
  <pre class="lang-php prettyprint-override"><code>$begin_date_2021_2022='01-09-2021';
  for ($i=0; $i &lt;5 ; $i++) { 
      $begin_date_2021_2022=date('d/m/Y',strtotime('+1 month', strtotime($begin_date_2021_2022))) ; 
      echo $begin_date_2021_2022.&quot;&lt;br&gt;&quot;;
  } 
  </code></pre>
  <p>Output:</p>
  <pre class="lang-none prettyprint-override"><code>01/10/2021&lt;br&gt;
  10/02/2021&lt;br&gt;
  02/11/2021&lt;br&gt;
  11/03/2021&lt;br&gt;
  03/12/2021&lt;br&gt;
  </code></pre>
  <p>My expectation is</p>
  <pre class="lang-none prettyprint-override"><code>01/10/2021&lt;br&gt;
  01/11/2021&lt;br&gt;
  01/12/2021&lt;br&gt;
  01/01/2022&lt;br&gt;
  01/02/2022&lt;br&gt;
  </code></pre>
  <p>Where is the problem?</p>