PHP Variable Undefined [duplicate] - php

Question

This question already has answers here:
"Notice: Undefined variable", "Notice: Undefined index", "Warning: Undefined array key", and "Notice: Undefined offset" using PHP
(29 answers)
Closed 4 years ago.
i get this php error
Notice: Undefined variable: total_earn in /var/www/..../hello.php on
line 221
But the variable works fine..
anyone can help me & have an idea ?
<?php
$con=mysqli_connect("localhost:3306","***","***","superpayment");
$a="select * from users where ref='".$req_user_info['refer']."' ";
$b=mysqli_query($con,$a);
$c=mysqli_fetch_array($b);
$mm="select * from configuration where config_name='refer_referer_points' ";
$nn=mysqli_query($con,$mm);
$oo=mysqli_fetch_array($nn);
if($c['id']>0) {
$x="select * from users where ref='".$req_user_info['refer']."' ";
$q=mysqli_query($con,$x);
$i=0;
while($res=mysqli_fetch_array($q))
{
$i++;
$x="select count(*) as ld, sum(points_used) as earn from Completed where username='".$res['username']."' ";
$y=mysqli_query($con,$x);
$z=mysqli_fetch_array($y);
$user_earn=$z['earn']/1000;
$your_earn=($user_earn*$oo['config_value'])/100;
$total_earn=$total_earn+$your_earn;
?>

Answer 1

The jist of it, is $total_earn is not yet initialized when you're doing $total_earn=$total_earn+$your_earn;. While PHP will automatically initialize it (As 0), it's letting you know that by not initializing it, it could be a bug in your code.
It's helpful when you may accidentally misspell a variable. See this post for more information on this.
Set it like so:
$i=0;
$total_earn=0;
while($res=mysqli_fetch_array($q))
{
$i++;
$x="select count(*) as ld, sum(points_used) as earn from Completed where username='".$res['username']."' ";
$y=mysqli_query($con,$x);
$z=mysqli_fetch_array($y);
$user_earn=$z['earn']/1000;
$your_earn=($user_earn*$oo['config_value'])/100;
$total_earn=$total_earn+$your_earn;