make a value selected in drop down when editing - php

Question

I am adding a feature to edit the ads a user puts. For that I want to make the value selected which is selected by the user when he entered the values . How can I implement this?
<div class="nm">
Category
</div>
<div class="fl">
<select name="category" id = "ad_category" onchange="cangeSubCat(this.value)" >
<option value="">---Select Category---</option>
<option value="real_estate">Real Estate</option>
<option value="hotels_resturants">Hotels and Resturants</option>
<option value="car">Car Rental</option>
</select>
</div>

Answer 1

Add the selected HTML <option> attribute, in XHTML it is selected="selected".
<option value="value" selected>title</option>
^^^^^^^^
Documentation: http://www.w3.org/TR/html4/interact/forms.html#h-17.6.1
I mean how will I know which one should be selected..it will be different for different users . I wnt it to be selected which user selects during adding the ad
That depends on your code. You can do this with an array with all value/title pairs (value => title) and the value which is selected. Then when key (value) equals the selected one, the attribute is added in output. As it's an array it's easy to iterate over it.
$otpions = array(
'a' => 'A',
'b' => 'B',
);
$selected = 'b';
echo '<select>';
foreach ($options as $value => $title)
{
printf('<option value="%s" %s>%s</option>',
$value, $selected == $value ? 'selected' : '', $title);
}
echo '</select>';

Answer 2

okay lets assume you fetch value from db and that select box value is in $select variable then you've to write
<option <?php if($select=="real_estate") { echo "selected='selected'"; } ?> value="real_estate">Real Estate</option>
<option <?php if($select=="hotels_resturants") { echo "selected='selected'"; } ?> value="hotels_resturants">Hotels and Resturants</option>
<option <?php if($select=="car") { echo "selected='selected'"; } ?> value="car">Car Rental</option>

Answer 3

You can use this magic function
function __selectedDb($ctrlValue,$dbValue)
{
if($ctrlValue == $dbValue)
return "selected='selected'";
else
return "";
}
like
<select name="category" id = "ad_category" onchange="cangeSubCat(this.value)" >
<option value="" <?php echo __selectedDb("","$cat")?>>---Select Category---</option>
<option value="real_estate" <?php echo __selectedDb("real_estate","$cat")?>>Real Estate</option>
<option value="hotels_resturants" <?php echo __selectedDb("hotels_resturants","$cat")?>>Hotels and Resturants</option>
<option value="car" <?php echo __selectedDb("car","$cat")?>>Car Rental</option>
</select>
I write in core php please convert php code to smarty