Three forms of php array output detail

$bbbb=array("11"=>"aaa","22"=>"bbb");
// Output value only value Can't output key
foreach($bbbb as $color)
{
　　echo $color;
}
//value with key Can be output 
foreach($bbbb as $key=>$value)
{
　　echo $key."=>".$value;
}

//value with key Can be output 
while($color=each($bbbb)){
　　echo $color['key'];
}
 or 
while(list($key,$value)=each($bbbb)){
　　echo "$key : $value<br>";
}

Direct access to array elements:

<?php
$arr=array('w'=>'wen','j'=>'jian','b'=>'bao');
echo($arr['w']),'<br/>';// Play a role 
echo($arr[w]),'<br/>';// Play a role 
echo($arr[0]),'<br/>';// It doesn't work, somehow...? 
echo($arr['j']),'<br/>';// Play a role 
echo($arr[j]),'<br/>';// Play a role 
echo($arr[1]),'<br/>';// It doesn't work, somehow...? 
echo($arr['b']),'<br/>';// Play a role 
echo($arr[b]),'<br/>';// Play a role 
echo($arr[2]),'<br/>';// It doesn't work, somehow...? 
?>

Output:

wen
wen
jian
jian
bao
bao

Suspect:
Accessing associative array elements,
1. The key in [] can be accessed without quotation marks (" ").
2, array index access is not working??

<?php
$arr1=array('wen','jian','bao');
echo $arr1[0],'<br/>',$arr1[1],'<br/>',$arr1[2];
?>

Output:

wen
jian
bao