The inserted value kept being a 0 - php

Question

I don't know what's going on, I selected the price in the table, and when I use it it's fine. In the <form> the $seller and $_SESSION['username'] also fine, but in the buy_item.php when I try to calculate $newAmount = ($row["amount"] - $price); and tried to see the value it seems like $price became 0$.
PAGE.PHP
The sql
$sql = "SELECT seller,price FROM stuff ";
in the table (ALL informations appears fine)
while($row = $result->fetch_assoc()) {
echo "<tr>";
echo "<td>". $row["price"] . "</td>";
echo "<td>". $row["seller"] . "</td>";
echo " <td><form action='buy_item.php' method='post'>
<input type='hidden' id='seller' name='seller' value='".$row['seller']."'/>
<input type='hidden' id='price' name='price' value='".$row['price']."'/>
<input type='hidden' id='buyer' name='buyer' value='". $_SESSION['username'] ."'/>
<input type='submit' value='Buy'/>
</form></td>";
echo "</tr>";
BUY_ITEM.PHP
<?php
session_start();
$conn = mysqli_connect("hi", "hi", "hi", "hi");
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$seller = mysqli_real_escape_string($link, $_REQUEST['seller']);
$price = mysqli_real_escape_string($link, $_REQUEST['price']);
$buyer = mysqli_real_escape_string($link, $_REQUEST['buyer']);
$sql = "SELECT username,amount FROM users WHERE username = '" .
$_SESSION['username'] . "'";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
while($row = $result->fetch_assoc()) {
if ($row["amount"] >= $price) {
$newAmount = ($row["amount"] - $price);
echo ("$newAmount");
}
else
{
echo "Records added successfully.";
}
}
} else { echo "0 results"; }
$conn->close();
?>
the $newAmount always show up = $amount cause $price always become = 0

Answer 1

I'm going to take a punt and say that $price has a hidden character or the like in it.
PHP practices type juggling. Internally PHP is a typed language which casts the real type as required.
$_REQUEST provides the value of $price as a string.
When you use it in a subtraction PHP casts it from a string to an integer. Something goes wrong in the cast, it doesn't look like a number, so PHP makes it zero. Your results then occur.
Printing it out with var_dump() as #mr-glass suggested will make this clear.