A simple calculator

Page 1.php

<?php
include 'page3.php';
$cal=new calc();
$a=10;$b=20;
$ch='*';
switch($ch)
{
    case '+': echo $cal->add($a,$b);
              break;
    case '-': echo $cal->sub($a,$b);
              break;
    case '*': echo $cal->mul($a,$b);
              break;
    case '/': echo $cal->div($a,$b); 
              break;
        
}

?>

Page2

<?php
class calc
{
    public function add($a,$b)
    {
            return $a+$b;
    }
    public function sub($a,$b)
    {
        return $a-$b;
    }
    public function mul($a,$b)
    {
        return ($a*$b);
    }
    public function div($a,$b)
    {
        return $a/$b;
    }
    
}