Standard input is empty

Array
(
    [0] => a
    [1] => b
    [c] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 3
        )

)

PHP Warning:  Use of undefined constant a - assumed 'a' (this will throw an Error in a future version of PHP) in /home/LvJGaI/prog.php on line 2
PHP Warning:  Use of undefined constant b - assumed 'b' (this will throw an Error in a future version of PHP) in /home/LvJGaI/prog.php on line 2
PHP Warning:  Use of undefined constant c - assumed 'c' (this will throw an Error in a future version of PHP) in /home/LvJGaI/prog.php on line 2