OOPS

  <?php class Calculation {     public $a , $b , $c ;     function sum ()     {         $this -> c = $this -> a + $this -> b ;         return $this -> c ;     }     function sub ()     {         $this -> c = $this -> a - $this -> b ;         return $this -> c ;     } } $c1 = new Calculation (); $c2 = new Calculation (); echo "Value of a is : " . $c1 -> a = 20 ; echo "<br>" ; echo "Value of b is : " . $c1 -> b = 10 ; echo "<br>" ; echo "Sum is : " . $c1 -> sum () . "<br>" ; echo "Subtraction is : " . $c1 -> sub () . "<br><br>" ; echo "Value of a is : " . $c2 -> a = 50 ; echo "<br>" ; echo "Value of b is : " . $c2 -> b = 35 ; echo "<br>" ; echo "Sum is : " . $c2 -> sum () . "<br>" ; echo "Subtrac...