Form With Selection to MYSQL - PHP

[Hamza1]

I want to use this form with multiple select box to put data to database. I can put all data, but I can't put selections. What I am missing?

HTML FORM:

<form action="insertcheckbox.php" method="POST">

        <div class="modal-body">

            <div class="form-group">
                <label> Ime i Prezime </label>
                <input type="text" name="ime" class="form-control" placeholder="Upišite Ime i Prezime">
            </div>
            <div class="form-group">
                <label> Upišite Spol </label>
                <input type="text" name="spol" class="form-control" placeholder="Upišite Spol (M/Ž)">
            </div>
            <div class="form-group">
                <label>Grad</label>
                <input style="font-style: #f89900" type="text" name="grad" class="form-control" placeholder="Upišite Grad iz kojeg dolazi Student">
            </div>
            <div class="form-group">
                <label>Telefon</label>
                <input style="font-style: #f89900" type="text" name="tel" class="form-control" placeholder="Upišite Telefon">
            </div>
            <div class="form-group">
                <label>Email</label>
                <input style="font-style: #f89900" type="email" name="email" class="form-control" placeholder="Upišite Email">
            </div>
            <div class="form-group">
                <label>Uzrast</label>
                <input style="font-style: #f89900" type="text" name="uzrast" class="form-control" placeholder="Upišite Uzrast">
            </div>
            <div class="form-group">
                <label>Škola</label>
                <input style="font-style: #f89900" type="text" name="skola" class="form-control" placeholder="Upišite Obrazovnu Ustanovu">
            </div>

            <div class="form-group">
              <label>Izaberite Programe sa liste</label>
             <select name="naziv[]" id="naziv" class="form-control action" multiple="">
              <option disabled selected>-- Izaberi Program --</option>
              <?php
                include "config/database.php";  // Using database connection file here
                $records = mysqli_query($conn, "SELECT naziv FROM program");  // Use select query here 

                while($data = mysqli_fetch_array($records))
                {
                echo "<option value='". $data['naziv'] ."'>" .$data['naziv'] ."</option>";  // displaying data in option menu
                } 
              ?>  
            </select> 
            </div>
        </div>
        <div class="modal-footer">
            <button type="button" class="btn btn-secondary" data-dismiss="modal">Zatvori</button>
            <button type="submit" value="submit" name="registerbtn" class="btn btn-primary">Pošalji</button>
        </div>
      </form>

PHP FORM:

<?php
include_once 'config/database.php';
if(isset($_POST['Register']))
{  
   $ime = $_POST['ime'];
   $spol = $_POST['spol'];
   $grad = $_POST['grad'];
   $tel = $_POST['tel'];
   $email = $_POST['email'];
   $uzrast = $_POST['uzrast'];
   $skola = $_POST['skola'];
   $naziv = $_POST['naziv'];
   $sql = "INSERT INTO students (ime, spol, grad, tel, email, uzrast, skola, naziv)
   VALUES ('$ime','$spol','$grad','$tel', '$email', '$uzrast', '$skola', '$naziv')";
   if (mysqli_query($conn, $sql)) {
    echo "New record created successfully !";
   } else {
    echo "Error: " . $sql . "
" . mysqli_error($conn);
   }
   mysqli_close($conn);
}
?>

[Ishan Shah]

You are Storing multiple select box values to an array so, save the values to the database using comma-separated.

$naziv = implode(',', $_POST['naziv']);