evaluating dynamic variable

Hi, I'm having trouble evaluating a dynamic variable. I want to check if the variable $_POST["resolutions$i"] is an empty string, as you'll see from the code. However, every way I've tried to check the variable so far (including empty() and eval()) always returns a null value, even when the variable should contain a value. I've probably been doing something wrong in my previous efforts. Can someone recommend a way to reliably evaluate this variable? for ($i=1; $i<=$entries; $i++) { if($_POST["resolutions$i"] !== ''){ do_something(); } } Thanks.