php - 计算输出不理想

Question

我试图在这里了解类定义和使用计算的基础知识

这是代码

<?php

class calculator {
    var $number1 = 4;
    var $number2 = 5;

    function add ($a,$b){
        $c = $a + $b;
        print ("the sum of your numbers: $c");
        print ($c);
    }

}

$cal = new calculator;
$cal->add($number1,$number2);

?>

在我的浏览器中出现的是:

The sum of your numbers: 0

为什么不是 9？

Answer 1

你要么做

class calculator {
    //...
}
$number1 = 4;
$number2 = 5;
$cal = new calculator;
$cal->add($number1,$number2);

或

class calculator {
    var $number1 =4;
    var $number2 =5;
    //...
}
$cal = new calculator;
$cal->add($cal->number1,$cal->number2);