Simple PHP class -

i learning php , created below class, can't seem figure out why giving me below errors says:

144

warning: missing argument 1 setters::set_a(), called in c:\xampp\htdocs\php\accessmod2.php on line 19 , defined in c:\xampp\htdocs\php\accessmod2.php on line 9

notice: undefined variable: value in c:\xampp\htdocs\php\accessmod2.php on line 11

<?php  class setters{     private $a = 144;     public function get_a(){         return $this->a;     }      public function set_a($value){          $this->a = $value;     } }  $example = new setters();  echo $example->get_a()."<br />"; $example->set_a(15)."<br />"; echo $example->set_a()."<br />";  ?> 

you have use parameter set() function. in case, think want see if set() function have work. use get() function.

so change :

echo $example->get_a()."<br />"; $example->set_a(15)."<br />"; echo $example->get_a()."<br />"; 

and result :

144 15