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I'm trying to get my head around constructors and PHP in general, but what I'm trying to achieve here is a way of calculating the volume, diameter and area of a circle with PI and FOUR_THIRDS as constants in the class.

My code keeps saying there is an error with the constants saying they are undefined but I copied the method from php.net. Then the $radius is also showing up as an undefined variable, so should I add $radius = 1; somewhere into the class to define it, is that what it means by defining? 

<?php

class SphereCalculator {

const PI = 3.14;
const FOUR_THIRDS =4/3;



    public function __construct($radius){
        $this->classRadius = $radius;
    }

    public function setRadius ($radius){
        $this->classRadius = $radius;
    }

    public function getRadius(){
        return $this->classRadius;
    }


    public function getVolume () {

        return FOUR_THIRDS * PI * ($this->classRadius * $this->classRadius);
    }


    public function getArea () {

        return PI * ($this->classRadius * $this->classRadius);
    }

    public function getDiameter () {

        return $this->classRadius += $this->classRadius;
    }

}

$mySphere = new SphereCalculator ();
$newRadius =$mySphere->radius; 
$newRadius = 113;

echo "The volume of the circle is ".$mySphere->getVolume ()."<br>";
echo "The diameter of the circle is ".$mySphere->getDiameter ()."<br>";
echo "The area of the circle is ".$mySphere->getArea ()."<br>";



?>
user229044
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cigarette_unicorn
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    Class constants are referenced as `self::FOUR_THIRDS` (inside the class) or `SphereCalculator::FOUR_THIRDS` (from outside the class); global constants are referenced as `FOUR_THIRDS`.... you have defined class constants – Mark Baker May 01 '16 at 21:08
  • For diameter; don't use `+=`, simply use `+`, otherwise you actually double the value of the `classRadius` property every time you call `getDiameter()` – Mark Baker May 01 '16 at 21:11
  • Also, you're missing a `* $this->classRadius` - volume is 4/3 PI R^3 – Niet the Dark Absol May 01 '16 at 21:11
  • And there's no instance property named `classRadius`. Plus, you aren't passing any value to the constructor method. – Rajdeep Paul May 01 '16 at 21:12
  • Note that `FOUR_THIRDS =4/3;` works since PHP 5.6+ only. – trincot May 01 '16 at 21:13
  • There are multiple ways to define constants in PHP. I think the answer you are looking is already in this post http://stackoverflow.com/questions/2447791/define-vs-const. – ashish May 01 '16 at 21:17
  • Thank you all for your help! I have changed the constants and added the extra `$this->classRadius` (good spot!) but I am still running a few errors: Missing argument 1 for SphereCalculator::__construct() Undefined variable: radius Undefined property: SphereCalculator::$radius – cigarette_unicorn May 01 '16 at 21:36
  • Rajdeep Paul, I'm not sure how to do an instance property or pass value to the constructor? Sorry, I'm really new to coding :( – cigarette_unicorn May 01 '16 at 21:38

2 Answers2

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You need to define constant FOUR_THIRDS as floating value or integer value. You have defined with as 4/3 which is not acceptable.

Hence, you need to define as,

const PI = 3.14;
const FOUR_THIRDS = 1.33;

Since you have defined the constants inside the class, it takes it as member variable of the class itself. Hence, you will need to access the constants with self::PI.

Other problem with your php code is your defining the constructor wrong. You have an paramter while defining the constructor but in your main part of the code where you created the object, you have not passed the parameter.

Here is the link to the corrected PHP code: https://ideone.com/UOMUPf

ashish
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You should use constants using class name like ClassName::ConstantName, and if you are using within the class then you can use as self::ConstantName.

So, you should use your constants as self::PI and self::FOUR_THIRDS.

Hardik
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