in php how to check a field have blank/empty/null value
<p>i want to disply an error when some varaiable have blank value or empty or null value (whatever we say), variable is shown below:</p>

<pre><code> $mo=strtotime($_POST['MondayOpen']);
 where var_dump($_POST['MondayOpen']) return string(0) "".
</code></pre>

<p>now i want to solve below </p>

<ol>
<li><p>first of all i want to know  $mo is which type of variable (string or integer or other type of variable)</p></li>
<li><p>which function is better to find that $mo have no value</p></li>
</ol>

<p>i conduct a test with <code>$mo</code> and i got these results</p>

<pre><code>is_int($mo);//--Return nothing
is_string($mo); //--Return bool(false) 
var_dump($mo);  //--Return bool(true)                   
var_dump(empty($mo));//--Return bool(true) 
var_dump($mo==NULL);//--Return bool(true) 
var_dump($mo=='');//--Return nothing
</code></pre>
