PHP beginner. Trying to display UserId - php

Question

I am accessing my database on PhpMyAdmin, all my names etc are correct, but for some reason UserId is not working. Can someone point me in the right direction?
I have tried printing it but nothing displays.
<?php session_start();
$username = $_GET['username'];
$password = $_GET['password'];
// Create connection
$con=mysqli_connect("localhost","root","","test");
// Check connection
if (mysqli_connect_errno($con))
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
$result = mysqli_query($con,"SELECT * FROM user2 where username='$username' and password='$password'");
$row_cnt = mysqli_num_rows($result);
if($row_cnt >0){
while($row = mysqli_fetch_array($result)){
$UserId = $row['UserId'];
}
$sqlQuery2 = "SELECT ProductID, Name, Price, Description FROM product";
echo "Hello ".$username."<br>" .$UserId. "<br> This is a list of products";
$result2 = mysqli_query($con,$sqlQuery2);
echo "<table border='1'>
<tr>
<th>ProductID</th>
<th>Name</th>
<th>Price</th>
<th>Description</th>
<th>View</th>
</tr>";
while($row = mysqli_fetch_array($result2))
{
echo "<tr>";
echo "<td>" . $row['ProductID'] . "</td>";
echo "<td>" . $row['Name'] . "</td>";
echo "<td>" . $row['Price'] . "</td>";
echo "<td>" . $row['Description'] . "</td>";
echo "<td><a href=\"detailview.php?ProductID=".$row['ProductID']."\"'>Detailed View</a></td>";
echo "</tr>";
}
echo "</table>";
mysqli_close($con);
?>
Update My Details
<?php } else{
echo "invalid login "; }
?>

Answer 1

use var_dump($var) to see what is in the variable
1st check what is returned in $result and after check $UserId before using it
after the while check if $UserId is set (if the condition is false, ou var is not set..) you should check $row_count too
you should indent your code
here is your code reindented :
<?php session_start();
$username = $_GET['username'];
$password = $_GET['password'];
// Create connection
$con=mysqli_connect("localhost","root","","test");
// Check connection
if (mysqli_connect_errno($con))
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
$result = mysqli_query($con,"SELECT * FROM user2 where username='$username' and password='$password'");
$row_cnt = mysqli_num_rows($result);
if($row_cnt >0){
while($row = mysqli_fetch_array($result)){
$UserId = $row['UserId'];
}
$sqlQuery2 = "SELECT ProductID, Name, Price, Description FROM product";
echo "Hello ".$username."<br>" .$UserId. "<br> This is a list of products";
$result2 = mysqli_query($con,$sqlQuery2);
echo "<table border='1'>
<tr>
<th>ProductID</th>
<th>Name</th>
<th>Price</th>
<th>Description</th>
<th>View</th>
</tr>";
while($row = mysqli_fetch_array($result2))
{
echo "<tr>";
echo "<td>" . $row['ProductID'] . "</td>";
echo "<td>" . $row['Name'] . "</td>";
echo "<td>" . $row['Price'] . "</td>";
echo "<td>" . $row['Description'] . "</td>";
echo "<td><a href=\"detailview.php?ProductID=".$row['ProductID']."\"'>Detailed View</a></td>";
echo "</tr>";
}
echo "</table>";
mysqli_close($con);
?>
Update My Details
<?php
}
else
{
echo "invalid login ";
}
?>