#include <iostream>

struct safearray
{ 
  protected:             // protected things can only be accessed from within
    int data[100];       // safearray's own functions. Nobody else may do anything
                         // with the array 
    
  public:                // public means back to normal, everything accessible now 
    int size;
 
  int get(int pos)              // so this is the only function in the world that can show
  { if (pos<0 || pos>=size)     //  us the contents of the array. It is impossible to bypass
    { cerr << "error in get\n"; // the check for a valid position
      exit(1); }
    return data[pos]; }
 
  void put(int pos, int val)    // and this is the only function that can change the
  { if (pos<0 || pos>=size)     // array. We are safe from the other example's terrors.
    { cerr << "error in put\n";
      exit(1); }
    data[pos] = val; }
};

void main()
{ safearray A, B;
  A.size = 20;
  B.size = 90;
  cout << "A\n";
  for (int i=0; i < A.size; i+=1)
    A.put(i, i * 10001);
  cout << "B\n";
  for (int i=0; i < 123; i+=1)
    B.put(i,  i*2);
  B.data[345] = 6; }       // this last statement is illegal, we will get an error