Because you have nested arrays, then I actually recommend a recursive approach:
function recurse_into_array( $in, $tabs = "" )
{
foreach( $in as $key => $item )
{
echo $tabs . $key . ' => ';
if( is_array( $item ) )
{
recurse_into_array( $item, $tabs . "\t" );
}
else
{
echo $tabs . "\t" . $key;
}
}
}
recurse_into_array( $_POST );