title: PHP add date based in user selection
body: <p>I want to add 'x' number of days to current date. The days will be select by user and add to current date.
  Below is my select days code</p>
  
  <pre><code>&lt;html&gt;
  &lt;head&gt;
      &lt;meta charset="UTF-8"&gt;
      &lt;title&gt;Date&lt;/title&gt;
  &lt;/head&gt;
  &lt;body&gt;
          &lt;form name=date method="post" action="test.php"&gt;
              &lt;table style="width: 60%;"&gt;
                  &lt;tr&gt;
                      &lt;td colspan="2" align="center"&gt;&lt;h3&gt;Date&lt;/h3&gt;&lt;/td&gt;
                  &lt;/tr&gt;
                  &lt;tr&gt;
                      &lt;td&gt;&amp;nbsp;&lt;/td&gt;
                      &lt;td&gt;&amp;nbsp;&lt;/td&gt;
                  &lt;/tr&gt;
                  &lt;tr&gt;
                      &lt;td&gt;No. of Days&lt;/td&gt;
                      &lt;td&gt;
                          &lt;select name="days" style="width: 270px"&gt;
                              &lt;option value ="Select"&gt;Select&lt;/option&gt;
                              &lt;option value="7"&gt;7&lt;/option&gt;
                              &lt;option value ="14"&gt;14&lt;/option&gt;
                              &lt;option value ="21"&gt;21&lt;/option&gt;
                              &lt;option value ="28"&gt;28&lt;/option&gt;
                          &lt;/select&gt;
                      &lt;/td&gt;
                  &lt;/tr&gt;
                  &lt;tr align="center"&gt;
                      &lt;td&gt;&lt;input type='submit' value='Submit'&gt;&lt;/td&gt;
                      &lt;td&gt;&lt;input type='reset' value='Reset'&gt;&lt;/td&gt;
                  &lt;/tr&gt;
  
              &lt;/table&gt;
          &lt;/form&gt;
  &lt;/body&gt;
  </code></pre>
  
  <p></p>
  
  <p>Below is the code after submit </p>
  
  <pre><code>&lt;?php
  $date = date("Y-m-d");
  $days = $_POST["days"];
  echo date('Y-m-d', strtotime($date . ' + '. $_POST["days"]));
  ?&gt;
  </code></pre>
  
  <p>But the results will always show as "1970-01-01"</p>
  
  <p>Hope to get some tips. Thanks in advance</p>