php - Undefined Offset 0 , how can i set this array -

hello have undefined offset 0 . inside code.

$q = mysql_query("select * category"); if (false === $q) {     echo mysql_error(); }  while ($r = mysql_fetch_row($q)) {   $names[$r[0]] = $r[2];   $children[$r[0]][] = $r[1]; }  function render_select($root=0, $level=-1) {   global $names, $children;   if ($root != 0)     echo '<option>' . strrep(' ', $level) . $names[$root] . '</option>';   foreach ($children[$root] $child)     render_select($child, $level+1); }  echo '<select>'; render_select(); echo '</select>'; 

the exact line error :

foreach ($children[$root] $child)     render_select($child, $level+1); 

this selectbox tree format, found code in question

more efficient hierarchy system

there ambiguity in code here:

if ($root != 0)     echo '<option>' . strrep(' ', $level) . $names[$root] . '</option>';   foreach ($children[$root] $child)     render_select($child, $level+1); 

if attempting execute these 3 lines if $root != 0, need add curly braces this:

if ($root != 0) {     echo '<option>' . strrep(' ', $level) . $names[$root] . '</option>';     foreach ($children[$root] $child)     {         render_select($child, $level+1);     } } 

otherwise, anytime render_select called without parameter (or first parameter value of '0') attempt access element of $children @ array key '0'. error indicates, $children not contain value @ key.