POST throwing undefined index on every var - php

Question

I'm defining POST here:
else if(isset($_POST["Edit"])){
$result_set = $sqlConn->query("SELECT Art, Ime, Cijena, Kol FROM permatable WHERE Art='{$_POST["Art"]}' LIMIT 1");
$Item = $result_set->fetch_array();
$_POST["Art"] = $Item["Art"];
$_POST["Ime"] = $Item["Ime"];
$_POST["Cijena"] = $Item["Cijena"];
$_POST["Kol"] = $Item["Kol"];
header("Location: EditP.php");
}
Now the Post "Edit" and the if statment is being called just fine. I've also checked the query and it returns everything it needs to.
Now on the header location I get undefined index on all of these vars and thats coming from the following code:
echo "<input type='text' placeholder=".$_POST["Art"]." name='Art'>
<input type='text' placeholder=".$_POST["Ime"]. "name='Ime'>
<input type='text' placeholder=".$_POST["Cijena"]." name='Cijena'>
<input type='text' placeholder=".$_POST["Kol"]." name='Kol'>";
Am I doing something wrong? I can't see any mistakes myself and this has been bothering me for a while now.

Answer 1

That won't work.
you can't send POST with header location
you can try to add them to your url
foreach($item as $key=>$value)
{
$items .= $key."&".$value ;
}
header("Location: EditP.php?".$items);
and in the edit.php page
echo "<input type='text' placeholder=".$_GET["Art"]." name='Art'>
<input type='text' placeholder=".$_GET["Ime"]. "name='Ime'>
<input type='text' placeholder=".$_GET["Cijena"]." name='Cijena'>
<input type='text' placeholder=".$_GET["Kol"]." name='Kol'>";

Answer 2

You cannot redirect the user w/ POST variables. It will not work. Read here. The best way to do it is to create a form and then automatically submit it via JavaScript as soon as the page loads. Example:
<form id="my_form" action="http://example.com" method="post">
<input type="hidden" name="name" value="<?php echo htmlspecialchars($name); ?>">
<input type="hidden" name="email" value="<?php echo htmlspecialchars($email); ?>">
<input type="hidden" name="etc" value="<?php echo htmlspecialchars($etc); ?>">
</form>
<script type="text/javascript">
//Our form submission function.
function submitForm() {
document.getElementById('my_form').submit();
}
//Call the function submitForm() as soon as the page has loaded.
window.onload = submitForm;
</script>

Answer 3

$result_set = $sqlConn->query("SELECT Art, Ime, Cijena, Kol FROM permatable WHERE Art='($_POST["Art"])' LIMIT 1");
Try changing curly braces to small braces.

Answer 4

Well, I used SESSION at the end so I just changed the code to following:
$result_set = $sqlConn->query("SELECT Art, Ime, Cijena, Kol FROM permatable WHERE Art='{$_POST["Art"]}' LIMIT 1");
$Item = $result_set->fetch_array();
$_SESSION["Art"] = $Item["Art"];
$_SESSION["Ime"] = $Item["Ime"];
$_SESSION["Cijena"] = $Item["Cijena"];
$_SESSION["Kol"] = $Item["Kol"];
header("Location: EditP.php");
And for the EditP:
echo "<input type='text' placeholder=".$_SESSION["Art"]." name='Art'>
<input type='text' placeholder=".$_SESSION["Ime"]. "name='Ime'>
<input type='text' placeholder=".$_SESSION["Cijena"]." name='Cijena'>
<input type='text' placeholder=".$_SESSION["Kol"]." name='Kol'>";