Notice: Array to string conversion php

$gadget = array( 'computer', 'mobile', 'tablet' );
echo implode($arr);

// Use json_encode to collapse the array to json string:
$stuff = array(1,2,3);
print json_encode($stuff);   //Prints [1,2,3]

$person = [
    'name' => 'Jon',
    'age' => 26,
    'status' => null,
    'friends' => ['Matt', 'Kaci', 'Jess']
];

echo json_encode($person);
// {"name":"Jon","age":26,"status":null,"friends":["Matt","Kaci","Jess"]}

// use the builtin php function print_r or var_dump:
$stuff = array(1,2,3);
print_r($stuff);
$stuff = array(3,4,5);
var_dump($stuff);

$stuff = array(1,2,3);
print_r($stuff);
$stuff = array(3,4,5);
var_dump($stuff);

// suppress the Notices:
error_reporting(0);
print(array(1,2,3));    //Prints 'Array' without a Notice.