how to use an access declaration : private inheritance « Class « C++ Tutorial

1. C++ Tutorial
2. Class
3. private inheritance

#include <iostream>   
     using namespace std;

  class B_class {   
  public:   
    int i, j;   
  };   
       
  class D_class : private B_class {   
  public:   
    // access declaration   
    B_class::i;  // i from B_class is now public again   
       
    int k;   
  } ;   
       
  main(void)   
  {   
    D_class d;   
       
    d.i = 10;  // legal because i is made public in D_class   
    d.k = 20;   
       
    cout << d.i * d.k;   
       
    return 0;   
  }