PHP：下拉框中的选定值

I am doing an dropdown box, where I have let's say we have "option1" and "option2", the dropbox selects(marks) the "option1" and then we select the "option2", I want it to mark the "option2" in the dropdown box, but it doesn't mark it.

I'm trying to avoid to do javascript on this one, so I wonder if I can do it only on PHP.

Advices? Thanks!

Edit. Well the problem is that i dont know how many options i have before building the dropdown menu. I get an array generated from a table in a database and make the options based on that. Code:

<select name="department">
            <?php foreach(bloggModelControler::getDepartments($_SESSION['user']) as $tempDepartment){
                if(strcmp($tempDepartment, $department) == 0){
                    $selected = ".selected='selected'.";
                }else{
                    $selected = ".selected=''.";
                }
                $dropdown = "<option \"$selected\" value=\"$tempDepartment\">\"$tempDepartment\" Selected</option>";
                echo $dropdown;
}?>         
</select>

and $department:

<?php
        if(isset($_POST['department'])){
            $department = $_POST['department'];
        }else{
            $departments = bloggModelControler::getDepartments($_SESSION['user']);
            $department = $departments[0];
        }
    ?>

Updated answer based on updated question (included code)

Don't put the periods inside the text variables for 'selected'.

if(strcmp($tempDepartment, $department) == 0){
                $selected = "selected='selected'";
            }else{
                $selected = "selected=''";
            }

Previous answer

In your PHP code that generates the HTML for the Select box, you have to specify which option is selected.

For example:

<select name="selectbox">
  <option <?php if ($_POST['selectbox'] == 'option1') echo 'selected="selected"';?>>option1</option>
  <option <?php if ($_POST['selectbox'] == 'option2') echo 'selected="selected"';?>>option2</option>
</selected>

Alternate syntax:

<select name="selectbox">
  <option <?= ($_POST['selectbox'] == 'option1')? 'selected="selected"' : '';?>>option1</option>
  <option <?= ($_POST['selectbox'] == 'option2')? 'selected="selected"' : '';?>>option2</option>
</selected>