Post back the data if validation fails for "Select" - php

Question

Once submitted selected option, the data is not stored.
just want to know how to post back the data if validation fails
The following line doesnt really work for me.
<select id="numbers" name="numbers" value="<?php echo (isset($_POST['numbers'])) ? $_POST['numbers'] : " "; ?>"/>
if someone could give me a hand?
Many thanks, here is my code
<?php
if(isset($_POST['numbers']) &&($_POST['fruits']) && $_POST['numbers'] != "null" && $_POST['fruits'] !== "null")
{
echo "Thank you!";
} elseif (isset($_POST['numbers']) && $_POST['numbers'] = "null") {
echo "you forgot to choose a number";
}
elseif(isset($_POST['fruits']) && $_POST['fruits'] = "null")
{
echo "you forgot to choose fruit name";
}
?>
<form id="form" name="form" method="post" action="">
<label for="expiry">Select</label>
<select id="numbers" name="numbers" value="<?php echo (isset($_POST['numbers'])) ? $_POST['numbers'] : " "; ?>"/>
<option value="null" selected="selected">-</option>
<option value="01">01</option>
<option value="02">02</option>
<option value="03">03</option>
</select>
<select id="fruits" name="fruits" value="<?php echo (isset($_POST['fruits']))? $_POST['fruits'] : ''; ?>"/>
<option value="null" selected="selected">-</option>
<option value="Apple">Apple</option>
<option value="Banana">Banana</option>
<option value="Pear">Pear</option>
</select>
<input type="submit" value="Send" />
</form>
Solved it, Maybe not a best way, but at least got it sorted:
<?php
$item = null; #
$itemyear = null;
if(isset($_POST['numbers'])){
$item = $_POST['numbers'];
}
if(isset($_POST['fruits'])){
$itemyear = $_POST['fruits'];
}
if(isset($item) && isset($itemyear) && $item != "null" && $itemyear !== "null")
{
echo "Thank you!";
} elseif ($item == "null") {
echo "you forgot to choose a number";
}
elseif($itemyear == "null")
{
echo "you forgot to choose fruit name";
}
?>
<form id="form" name="form" method="post" action="">
<label for="expiry">Select</label>
<select id="numbers" name="numbers" />
<option value="null" selected="selected">-</option>
<option value="01" <?php if($item == '01'): echo "selected='selected'"; endif; ?>>01</option>
<option value="02" <?php if($item == '02'): echo "selected='selected'"; endif; ?>>02</option>
<option value="03" <?php if($item == '03'): echo "selected='selected'"; endif; ?>>03</option>
</select>
<select id="fruits" name="fruits" />
<option value="null" selected="selected">-</option>
<option value="Apple"<?php if($itemyear == 'Apple'): echo "selected='selected'"; endif; ?> >Apple</option>
<option value="Banana"<?php if($itemyear == 'Banana'): echo "selected='selected'"; endif; ?>>Banana</option>
<option value="Pear"<?php if($itemyear == 'Pear'): echo "selected='selected'"; endif; ?>>Pear</option>
</select>
<input type="submit" value="Send" />
</form>
<?php
echo $item ."-". $itemyear;
?>

Answer 1

the PHP isset() function returns either true or false (depending on whether the input is.. well... set.
You would want to use this:
value='<?php echo (isset($_POST['numbers'])) ? $_POST['numbers'] : ""; ?>

Answer 2

You can't set a value attribute on a <select>. You have to find the correct <option> and set its selected attribute. Personally, I put a data-default attribute on the <select> and then use JavaScript to loop through the options and find the right one.

Answer 3

Oh now I see.
I don't know what the usual thing to do is but one way is to put all the data as a query string when you redirect the user back. The reason why it doesn't stay in the $_POST global is because it's only kept on the page you post to then it's gone.
So when you redirect the user back
if(validationFailed)
{
header("Location: page.php?data=example");
}
The data can then be retrieved in page.php by using
$data = $_GET['data']; // contains "example"