How to use protected members

using System; //www  . j a  va  2s.  c  om
 
class BaseClass { 
  protected int i, j; // private to BaseClass, but accessible by D 
 
  public void set(int a, int b) { 
    i = a; 
    j = b; 
  } 
 
  public void show() { 
    Console.WriteLine(i + " " + j); 
 } 
} 
 
class DerivedClass : BaseClass { 
  int k; // private 
 
  // DerivedClass can access BaseClass's i and j 
  public void setk() { 
     k = i * j; 
  } 
 
  public void showk() { 
    Console.WriteLine(k); 
  } 
} 
 
class MainClass { 
  public static void Main() { 
    DerivedClass ob = new DerivedClass(); 
 
    ob.set(2, 3); // OK, known to DerivedClass 
    ob.show();    // OK, known to DerivedClass 
 
    ob.setk();  // OK, part of DerivedClass 
    ob.showk(); // OK, part of DerivedClass 
  } 
}