Notice: Undefined offset: 0 in

Question

I am getting this PHP error, what does it mean?

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

You are asking for the value at key 0 of $votes. It 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"