public $width = $_POST['width'];

<?php


Class Rectangle {

  //Declare the attributes:
  public $width ;
  public $height ;
  protected static $formula = 0;
 
  public function __construct($width, $height)
  {
    $this->width = $width;
    $this->height = $height;
  }

//Method to set the dimensions.
  Function create_formula()
  {
    self :: $formula = $this->width * $this->height;
  }

  //Method to set the dimensions.
  Function set_size($w = 0, $h = 0) {
      $this->width = $w;
      $this->height = $h;
      $this->create_formula();
  }

  //Method to calculate and return the area.
  function get_area() {
      return (self::$formula);
      }
  }
 
  Class Triangle extends Rectangle{
    Function create_formula() {
      self :: $formula = ($this->width * $this->height)/2;
    }
  }



?><h2>OOP Class Demo</h2>
<p>
Please enter two numbers to calculate the area of rectangle or tringle and press submit...
<p>
<form method="post" action="demo.php">
<br>width<input type=text name=num_a>
<br>height<input type=text name=num_b>
<br><input type="radio" name="shape" value="Rectangle" /> Rectangle
<br><input type="radio" name="shape" value="Tringle" /> Tringle
<br><input type=submit>
</form>



<?php
 
  echo("<br>");
  if(isset($_POST['submit']))
   {echo "THERE is submit.!";
 
   
  if (!$_POST['shape']){echo('your choice is: '.$_POST['shape']);}
  // create object of rectangle and calculate it is area
  $rect = new Rectangle ($_POST['width'], $_POST['height']);
  echo ($rect->get_area()."<br />");
 
  // create object of tringle and calculate it is area by extends
  $tri = new Triangle ($_POST['width'], $_POST['height']);
  echo $tri->get_area();
  }
 
?>

<?php

abstract class Shape
{
  protected $width;
  protected $height;

  public function __construct($width, $height)
  {
    $this->SetSize($width, $height);
  }

  public function SetSize($width, $height)
  {
    $this->width = $width;
    $this->height = $height;
  }

  public abstract function GetArea();
}


class Rectangle extends Shape
{
  public function GetArea()
  {
    return $this->width * $this->height;
  }
}

class Triangle extends Shape
{
  public function GetArea()
  {
    return $this->width * $this->height * .5;
  }
}




?>

<h2>OOP Class Demo</h2>
<p>
Please enter two numbers to calculate the area of rectangle or tringle and press submit...
<p>
<form method="post" >
<br>width<input type=text name='width'>
<br>height<input type=text name='height'>
<br><input type='submit' name='submit'>
</form>

<br/><br/>

<?php

if(isset($_POST['submit']))
{


  // create object of rectangle and calculate it is area
  $rect = new Rectangle ($_POST['width'], $_POST['height']);
  echo 'rectangle of this size would have the area of ', $rect->GetArea(), "<br />";
 
  // create object of tringle and calculate it is area by extends
  $tri = new Triangle ($_POST['width'], $_POST['height']);
  echo 'triangle of this sizes would have the area of ', $tri->GetArea();
}
 
?>