为什么我的foreach输入未设置？

Hey, I'm a novice at PHP, so have mercy on me!

I'm trying to echo $qty, but it's saying that the variable is an undefined variable.

If you see anything I'm doing wrong, feel free to tell me!

Thanks in advance!

action.php:

            foreach ($rows as $row){
              $food = $row['food'];
              $price = $row['price'];
              if(isset($_POST['qty'])){
                $qty = $_POST['qty'];
                echo 'set';
              }else{
                  echo 'unset';

              }
              echo "<tr>
            <td>$food</td>
            <td>$qty</td>
            <td>$price</td>
        </tr>";      
        }

order.php:

            foreach ($rows as $row) {
            $food = $row["food"];
            $price = $row["price"];
            $picture = $row["picture"];
            $description = $row["description"];
            $id = $row['id'];
            echo "<tr>
                    <td><img src='$picture' width='120px' /></td>
                    <td>$food</td>
                    <td>$$price</td>
                    <td><input type='number' min='0' max='10' placeholder='#' name='qty' maxlength='1'></td>
                </tr>";
        }

It seems almost certain then that if(isset($_POST['qty'])){ didn't pass, so the variable wasn't given a value. Make sure you are passing POST data to this script

If I am correct, you should see the word "unset" in the output.

You could set $qty in advance so that no matter what, it will have a value, or give it a different value if your if statement is false:

//set a default value earlier
$qty = 'This is the default value!';

//or in the if statement
if(isset($_POST['qty'])){
  $qty = $_POST['qty'];
  echo 'set';
} else {
  $qty = 'qty wasn't given a value!';
  echo 'unset';
}

It's not defined because you're not POSTing(form submission) a field named qty

You're trying to use $qty when it isn't set. This occurs when $_POST['qty'] is empty. What you need to do is set a default value for it in those cases:

if(isset($_POST['qty'])){
    $qty = $_POST['qty'];
}else{
    $qty = 0;
}

Or use the ternary operator to make this a one-liner:

$qty = (isset($_POST['qty'])) ? $_POST['qty'] : 0;