json decode then encode not working in php code example

Example 1: php decode json object

<?php

$json = '{"firstName":"Peter","lastName:":"Silva","age":23}';

$personInfo = json_decode(json);

echo $personInfo->age;

?>

Example 2: php json decode not working on array

//"[{\"name\": \"bill\", \"score\": 0.7948127388954163}, {\"name\": \"john\", \"score\": 0.782698392868042}]";
//for json in above format try this
$r=json_decode(stripcslashes(trim($response,'"')));