often you need to "remember" what a user inputs in a form.
that's not a problem with textfields, but with selectboxes it's a bit harder...

keep selected combobox” makes use of the built-in PHP functions in_array( ) and count( ).

01 <?php
02   
03 // you need the values of your combobox in an array
04 $country_values = array('us','de','uk','fr','gb');
05  
06 if(isset($_POST['country']) && in_array($_POST['country'], $country_values))
07 {
08     $selected_country = $_POST['country'];
09     $country_output = 'you selected &quot;'.$_POST['country'].'&quot;';
10 }else{
11     // input default value, if empty the first variable will be shown
12     $selected_country = '';
13     $country_output = 'please select an option';
14 }
15  
16 $option_num = count($country_values);
17  
18 echo '
19     <form method="post" action="./">
20         <label>'.$country_output.'</label>
21         <select name="country">';
22   
23 for($x = 0; $x < $option_num; $x++)
24 {
25     // print the options
26     echo '
27             <option value="'.$country_values[$x].'"'.($country_values[$x] == $selected_country ? 
28                 ' selected="selected"' : '').'>'.$country_values[$x].'</option>';
29 }
30   
31 echo '
32         </select>
33         <input type="submit" value="check it out" />
34     </form>';
35  
36 ?>