Last Updated: July 10, 2017

Show Undefined index: cart when my shopping cart is empty

Here is my all code.
checkout.php
<?php sessionstart();
requireonce("../dataAccessLayer/dalSession.php");
requireonce("../dataAccessLayer/dalProduct.php");
requireonce("../dataAccessLayer/dalService.php");
?>
<?php include ("../header2.php");?>
<br>
<div class="w3-content " style="max-width:1400px; margin-top:40px;">

<div class="w3-row-padding">

<h1>Shopping Cart</h1><hr>
<table class="table table-striped table-hover table-bordered">
 <tbody>
 <tr>
 <th>Product</th>
 <th>Price</th>
 <th>Vat</th>
 <th>Discount</th>
 <th>Quantity</th>
 <th>Total Price</th>
 <th>Delete</th>
 </tr> 

 <?php

 if(isset($_POST['sub']))
 {

 for($i=0; $i<count($_SESSION['cart']); $i++)
 {
 //print "for loop in";
 if(isset($_POST['qty_' . $_SESSION['cart'][$i]]))
 {

 //print $_POST['qty_' . $_SESSION['cart'][$i]];
 $_SESSION['qty'][$i] = $_POST['qty_'.$_SESSION['cart'][$i]]; 
 }
 }

 }



 $total = 0;
 //$_SESSION['cart']=[];
 //if(isset($_POST['sub'])){ 
 for($i=0; $i<count($_SESSION['cart']); $i++) //line 57
 {
 $p = new Product();
 $p->product_id = $_SESSION['cart'][$i];
 $r = $p->SelectById();
 print "<tr>";

print "<td align=\"center\"></td>";
echo "<td align=\"center\">$r[2]"," TK","</td>";
echo "<td align=\"center\">$r[3]","%","</td>";
echo "<td align=\"center\">$r[4]","%","</td>";
print "<td align=\"center\">";

 ?>
 <form action="" method="post">
 <input type="text" name="qty_<?php print $_SESSION['cart'][$i];?>" value="<?php print $_SESSION['qty'][$i];?>">
 <input type="submit" name="sub" value="Update">
 </form>
 <?php 
 print "</td>";
 print "<td align=\"center\">";
 $price = $r[2] * $_SESSION['qty'][$i]; 
 echo "TK ".$t= $price + ($price * $r[3])/100 - ($price * $r[4])/100; 
 $total += $t; 
 print "</td>";
 print "<td align=\"left\"><a class=\"btn btn-danger\" href=\"cart_remove.php?id={$_SESSION['cart'][$i]}\">Remove</a></td>";

 print "</tr>";

 } 


 ?>

 <form action="purchase.php" method="post">

 <tr>
 <th colspan="5"><span class="pull-right">Total</span></th>
 <th><?php print "".$total." TK"; Session::Set("total",$total); ?></th>
 </tr>
 <tr>

 <td colspan="6"><a href="../index.php" class="btn btn-primary">Continue Shopping</a></td>
 <td colspan="5"><button type="submit" class="btn btn-success" name="sub" value="Confirm">
 Checkout <span class="glyphicon glyphicon-play"></span></button>
 </td>
 </tr> 
 </form>
</table>
</div>
<br>
</div>
</div>
</div>

<?php include ("footer.php");?>

dalSession.php

<?php

class Session
{
public static function Start(){
session_start();
}

public static function Set($key , $value){
 $_SESSION[$key] = $value;
}

public static function Get($key){
 if (isset($_SESSION[$key])) {
 return $_SESSION[$key];
 }
 else{
 return false;
 }
}

public static function Stop(){
 session_destroy();
 header("Location:user/login.php");
}

public static function StopA(){
 session_destroy();
 header("Location:../user/login.php");
}

public static function StopB(){
 session_destroy();
 header("Location:login.php");
}


public static function Check()
{
 self::Start();
 //echo $this->user_id;;
 if (self::Get("Mlogin")==false) 
 {
 self::Stop();
 header("Location:login.php");
 }
}

public static function CheckA(){
 self::Start();
 if (self::Get("Alogin")==false) {
 self::StopA();
 header("Location:../user/login.php");
 }
}

public static function CheckAll()
{
 if (self::Get("Mlogin")==false && self::Get("Alogin")==false) 
 {
 return false;
 }
 else
 {
 return true; 
 } 
}

public static function CheckUserLogin()
{self::Start();
 if (self::Get("Mlogin")==false) 
 {
 return false;
 }
 else
 {
 return true; 
 } 
}

public static function Auto(){
 self::Start();
 if(self::Get("Mlogin")==false){
 echo "<a style=\"color:white;\" href='user/login.php'>Login</a>";
 } else {
 echo "<a style=\"color:red;\" href='?action=logout'>Logout</a>";
 if(isset($_GET['action']) && ($_GET['action']== "logout")){
 self::Stop();
 }
 }

}

public static function AutoA(){
 self::Start();
 if(self::Get("Mlogin")==false){
 echo "<a style=\"color:white;\" href='login.php'>Login</a>";
 } else {
 echo "<a style=\"color:red;\" href='?action=logout'>Logout</a>";
 if(isset($_GET['action']) && ($_GET['action']== "logout")){
 self::StopB();
 }
 }

}

}

cart.php

<?php
requireonce("../dataAccessLayer/dalSession.php");
requireonce("../dataAccessLayer/dalComment.php");
require_once("../dataAccessLayer/dalProduct.php");
?>

<?php
$pro = new Product();
$pro->productid = $GET['id'];
$r = $pro->SelectById();
?>

addtocart.php

<?php
require_once("../dataAccessLayer/dalSession.php");

Session::Start();

if(isset($_GET['id']))
{

if(isset($_SESSION['cart']))
{
 $c=0;
 for($i=0; $i<count($_SESSION['cart']); $i++)
 { 
 if($_SESSION['cart'][$i] == $_GET['id'])
 {
 $c++;
 break;
 } 
 }
 if($c == 0)
 {
 $_SESSION['cart'][] = $_GET['id'];
 $_SESSION['qty'][] = 1;
 }

}
else
{
 $_SESSION['cart'][] = $_GET['id'];
 $_SESSION['qty'][] = 1; 
}

}
header("Location: details.php?id={$_GET['id']}");

#php