Gain Xp and level PHP & MYSQL - php

Question

I have this script for my site and I think I have a problem in the for line. If I update my user_xp_amount with 256 the script works fine. However, when I update with a higher XP, such as 785, the script is showing me that I have level 1 instead of level 2 with 256xp. Why is this not behaving the way I desire?
PHP Script:
<?php
$mysqli = new mysqli('localhost', 'user', 'pass', 'db');
$user_id = 4;
function get_user_xp($user_id, $mysqli) {
$sql = $mysqli->query("SELECT user_xp_amount FROM users_xp WHERE user_id='$user_id'");
$row = $sql->fetch_assoc();
return $row['user_xp_amount'];
}
$xp = array(0,256,785,1656,2654);
$my_xp = get_user_xp($user_id, $mysqli); // where 4 is my user id
for($i = 0; $i < count($xp); $i++) {
if($my_xp == $xp[$i]) {
echo 'I\'m on level ', ($i+1);
break;
}
else {
if(isset($xp[$i+1])) {
if($my_xp > $xp[$i] && $my_xp <= $xp[$i + 1]) {
echo 'My next level is ', ($i+2), ' and I need ', $xp[$i+1], ' more points for achieving it!';
break;
} else {
echo 'My next level is ', ($i+1), ' and I need ', $xp[$i], ' more points for achieving it!';
break;
}
}
}
}
?>
MySQL DB:
user_xp_id Primar bigint(20) | user_id bigint(20) | user_xp_amount bigint(20)

Answer 1

The reason it's not working can be found with some basic debugging: think through your for loop step by step. If that fails, try something like
// snip
for($i = 0; $i < count($xp); $i++) {
print $i; // show me which step I'm on
if($my_xp == $xp[$i]) {
// snip
Try that, and the reason will pop out at you.
This is an essential part of debugging: be careful what you assume. Your assumption is usually your mistake.
Only after you go through that exercise should you look any further into this answer. (You may not even want to!)
A hint that'll make it easier to code: you can keep reassigning values until you exit the loop.
$xp = array(0,256,785,1656,2654);
$my_xp = 254;
for($i = 0; $i < count($xp); $i++) {
// if we've looped beyond our xp, exit with last assigned (current) values
if($my_xp < $xp[$i]) { break; }
$my_level = $i;
// if index + 1 is in range, assign values
if($i+1<count($xp)) {
$next_level = $i+1;
$xp_needed = $xp[$i+1] - $my_xp;
// if index + 1 is out of range, give default values
} else {
$next_level = $i;
$xp_needed = 0;
}
}
printf("<div>Current Level: %d (%d xp)</div>" .
"<div>Next Level: %d (%d xp)</div>" .
"<div>XP Needed: %d</div>",
$my_level +1, // correct off-by-1 error of index
$my_xp,
$next_level +1, // correct off-by-1 error of index
$xp[$next_level],
$xp_needed
);