Allow one form submission cookie

Question

I have a form but I want it only being sent once per user, so I want to set a cookie to do that. How do I have to change my script?

My PHP script:

<?php
if (isset($_COOKIE["Form"]) == 1)
{
//Hide form
exit();
}
if ( $_GET['value'] <> "")
{   
$adress = 'Receiver@mysite.com';
$subject = 'SUBJECT';
$text = 'TEXT';
mail($adress,
$subject,   
$text,
'From: someone@mail.here');
  $handle = fopen ( "some-doc.txt", "a" );

  fwrite ( $handle, $_GET['value'] );

fclose ( $handle );


echo "Thanks";
setcookie("Form", 1, time()+3600*24*60); // Line 108
exit;
}
?>

Error Message

Warning: Cannot modify header information - headers already sent by (output started at
form.php:6) in 
form.php on line 108

I changed it but now I get this error.

Answer 1

I see that you did:

setcookie("Schule", 1, time()+3600*24*60);

Then use similar approach:

setcookie("Form", 'yes', time()+3600*24*60);

Now:

if (isset($_COOKIE["Form"]) && $_COOKIE["Form"] == 'yes')
{
//Hide form
exit();
}