I have issue with commerce_order_load_multiple function The way i am using this function is 

foreach ($mms as $mm) {
    $orders_of_user += commerce_order_load_multiple(array(), array('uid' =&gt; $mm-&gt;uid, 'status' =&gt; 'cart'));
  } 

But i am not getting anything output from this and when i use static value of integer in place of uid i am getting result..

 $orders_of_user += commerce_order_load_multiple(array(), array('uid' =&gt; 421, 'status' =&gt; 'cart'));


I don't understand what causing the problem in foreach
when i use static value of integer in place of uid i am getting result


Logically speaking, that can only mean that $mm-&gt;uid doesn't contain what you think it does.

Install the devel module and use the dpm function to inspect the var:

foreach ($mms as $mm) {
  dpm($mm);
}


That should tell you what's going wrong.