PHP OOP -> Sticky Form

<?php //Note : This is 100% working example, copy, paste and understand the code in real time. Save //the file as areaofTriangle.php and run it. You will see two text box with button. // This code explains caluclating area of a Rectangle, width * height, sticky form coding, //Writing custom function. It's like in-built functions of php. // The style of this code is Object oriented, It's not procedural. So you should have some //knowledge in oops concepts and running php scripts. It is a combination of php, oop, html //and css. // Aim : Getting user input through form text fields and displaying result area of rectangle. // Check for form submission: if ($_SERVER['REQUEST_METHOD'] == 'POST') { class Area { //variable declaration for function without arguments. var $width=3; var $height=3; var $result; //variable declaration for function with arguments. var $x; var $y; var $result1; //custom function declaration. Formula area of rectangle = width * //height. function calculateArea() { // function without arguments. $result = $this->width*$this->height; ?> <!-- applying inline css style using div --> <div class = "red" style = "color:red; font-weight:bold;"> <?php echo "From custom function without arguments " .$result; ?> </div> <?php echo "<br>"; }// end of function. //This function gets two inputs through arguments. function calArea($x,$y ) { $x = "".$_POST['wid']; // storing value received through //textbox. $y = "".$_POST['hei']; $result1 = $x*$y; //Golden part of the logic. ?> <div class = "orange" style = "color:orange; font-weight:bold;"> <?php echo "From custom function with argument, width is : " .$x; echo "<br>"; echo "From custom function with argument, height is " .$y; echo "<br>"; echo "From custom function with argument, Result Area of rectangle is : " .$result1; echo "<br>"; echo "<br>"; ?> </div> <?php //oop basic knowledge. // $x = 3; Assign number to variable. // $tes = $x; Assigining variable to anotother variable. // echo "With arguments " .$tes; // echo "<br>"; }// end of function with arguments. }// end of class area. // Creating object $ar = new Area(); //Accessing custom function or method through object. $ar->calculateArea(); $ar->calArea(4,6); // Here i had passed dummy values 4 and 6, it have no link to actual logic of the program. // Getting input from textfield and displaying it. echo 'Width you entered is : ' .$_POST['wid']; echo "<br>"; echo 'Height you entered is :' .$_POST['hei']; } // End of server if. ?> <h1>Area of Traingle - Custom function example through oops way. </h1> <form action="areaofTriangle.php" method="post"> <p>Enter Width of Rectangle : <input type="text" name="wid" /></p> <p> Enter Height of Rectangle : <input type = "text" name="hei" /> </p> <p><input type="submit" name="submit" value="Area of Rectangle" /> </p> </form> //Output //From custom function without arguments 9 //From custom function with argument, width is : 4 //From custom function with argument, height is 2 //From custom function with argument, Result Area of rectangle is : 8 //Width you entered is : 4 //Height you entered is :2 //Area of Traingle - Custom function example through oops way. //Enter Width of Rectangle : Text box to get width. //Enter Height of Rectangle : Text box to get height. //Area of Rectangle : Result Button.