Can't submit an input for later use. php - php

Question

I am trying to use a search bar to grab the users input but when i input and submit nothing happens, I its not submitting properly but i can't for the life of me find my mistake. I have copied the input code from a previously created login page which works fine and therefore baffles me even more.
<div class="container">
<div class="form-group">
<?php
$stocksymbol = "";
if ($_SERVER["REQUEST_METHOD"] == "POST") {
if (empty($_POST["stocksymbol"])) {
$stocksymbolErr = "Please enter Username.";
} else {
$stocksymbol = test_input($_POST["stocksymbol"]);
}
function test_input($data) {
$data = trim($data);
$data = stripslashes($data);
$data = htmlspecialchars($data);
return $data;
}}
$servername = "localhost";
$username2 = "root";
$password2 = "";
$dbname = "mydb";
$mysqli = new mysqli($servername, $username2, $password2, $dbname);
if ($mysqli->connect_error) {
die("Connection failed: " . $mysqli->connect_error);
}
$query = "SELECT * FROM tblstocks WHERE Symbol = '$stocksymbol'";
if ($result = $mysqli->query($query)) {
while ($row = $result->fetch_assoc()) {
$_SESSION['stockavailable'] = true;
$_SESSION['stock']= $row;
header('Location: item.php');
}
$result->free();
}
$mysqli->close();
?>
<form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">
<label for="stocksymbol">Search:</label>
<input type="text" class="form-control" id="stocksymbol">
<br><br>
<input type="submit" class="btn btn-default" name="submit" value="Submit">
</form>
</div>

Answer 1

The input element must have an attribute name with the value to be the key that you are expecting on the server i.e. stocksymbol to be able to receive whatever entered in the element.
<input type="text" class="form-control" id="stocksymbol" name="stocksymbol">