Auto fill city after typing in zip code - php

Question

I need to auto fill fill the CITY: form when typing in the zip code,
it says "undefiened variable: array on line.." where value="< ? php $array['navn'] ">
can someone help ?
http://i62.tinypic.com/hv5fkl.jpg
<div id="search">
<form name="input" action="" method="get">
POST:<input type="text" name="postcode"><br><br>
City:<input type="text" name="navn" value="<?php $array['navn'] ?>"><br><br>
<input type="submit" value="search">
</form>
</div>
</div>
<?php
if(isset($_GET['postcode'])){
$postcode = $_GET['postcode'];
$content = file_get_contents('http://oiorest.dk/danmark/postdistrikter/'. $postcode . '.json');
$array = json_decode($content, true);
echo $array['navn'];
echo "<br>";
}
?>

Answer 1

You'd want to always initialize variables. What happens is that you're trying to access a variable that hasn't been initialized yet.
<?php
$city = ''; // initialize containers
$postcode = '';
if(isset($_GET['postcode'])){
$postcode = $_GET['postcode'];
$content = file_get_contents('http://oiorest.dk/danmark/postdistrikter/'. $postcode . '.json');
$array = json_decode($content, true);
// when the request is made, then assign
$city = $array['navn'];
}
?>
<!-- so that when you echo, you'll never worry about undefined indices -->
<div id="search">
<form name="input" action="" method="get">
POST:<input type="text" name="postcode" value="<?php echo $postcode; ?>"><br><br>
City:<input type="text" name="navn" value="<?php echo $city; ?>"><br><br>
<input type="submit" value="search">
</form>
</div>
In this answer, what happens is that, upon first load (no json request yet), the values are empty but they are declared on top.
When you submit the form, then that variable assignment happens and substitutes the values into that container.
Simple Demo