Notice Undefined offset 0 in

Question

I am getting this PHP error and do not know what it means?

Notice: Undefined offset: 0 in C:\xampp\htdocs\mywebsite\reddit_vote_tut\src\votes.php on line 41

From this code:

<?php 
include("config.php"); 

function getAllVotes($id) 
{ 
        $votes = array(); 
        $q = "SELECT * FROM entries WHERE id = $id"; 
        $r = mysql_query($q); 
        if(mysql_num_rows($r)==1)//id found in the table 
{ 
        $row = mysql_fetch_assoc($r); 
        $votes[0] = $row['votes_up']; 
        $votes[1] = $row['votes_down']; 
} 
return $votes; 
} 

function getEffectiveVotes($id) 
{ 
                $votes = getAllVotes($id); 
                $effectiveVote = $votes[0] - $votes[1]; //ERROR THROWN HERE 
                return $effectiveVote; 
} 
$id = $_POST['id']; 
$action = $_POST['action']; 

//get the current votes 
$cur_votes = getAllVotes($id); 

//ok, now update the votes 

if($action=='vote_up') //voting up 
{ 

      $votes_up = $cur_votes[0]+1; //AND ERROR THROWN HERE 

      $q = "UPDATE threads SET votes_up = $votes_up WHERE id = $id"; 
} 
elseif($action=='vote_down') 
{ 

      $votes_down = $cur_votes[1]+1; 
      $q = "UPDATE threads SET votes_down = $votes_down WHERE id = $id"; 
}

$r = mysql_query($q); 
if($r) 
{ 

          $effectiveVote = getEffectiveVotes($id); 
          echo $effectiveVote." votes"; 
} 
elseif(!$r) //voting failed 
{ 
        echo "Failed!"; 
} 
?>

Answer 1

 I assume you are looking for the values at key 0 of $votes which is an array that does not contain that key. The array $votes is not set, so when PHP is trying to access the key 0 of the array, it encounters an undefined offset for [0] and [1] and throws the error.

If you have an array:

$votes = array('1','2','3');

We can now access:

$votes[0]; $votes[1]; $votes[2];

If we try and access:

$votes[3];

We will get the error "Notice: Undefined offset: 3"