#include <cstdio>
#include <cstdlib>

// define a pure virtual class Comparable
class Comparable {
public:
  Comparable(void) {}
  virtual int equals( const Comparable *b ) = 0;
  virtual int greaterthan( const Comparable *b ) = 0;
  virtual int lessthan( const Comparable *b ) = 0;
};

class Thing : Comparable {
  int value;

 public:
  Thing() {
    value = 0;
  }

  Thing(const int a) {
    value = a;
  }

  void set(const int a) {
    value = a;
  }

  int get(void) {
    return(value);
  }

  int equals( const Comparable *b ) {
    return( this->value == ((Thing *)b)->value );
  }

  int greaterthan( const Comparable *b ) {
    return( this->value > ((Thing *)b)->value );
  }

  int lessthan( const Comparable *b ) {
    return( this->value < ((Thing *)b)->value );
  }
};


class Thing2 : Comparable {
  unsigned char value;

 public:
  Thing2() {
    value = 0;
  }

  Thing2(const char a) {
    value = a;
  }

  void set(const char a) {
    value = a;
  }

  char get(void) {
    return(value);
  }

  int equals( const Comparable *b ) {
    return( this->value == ((Thing2 *)b)->value );
  }

  int greaterthan( const Comparable *b ) {
    return( this->value > ((Thing2 *)b)->value );
  }

  int lessthan( const Comparable *b ) {
    return( this->value < ((Thing2 *)b)->value );
  }
};

int ComparableSort(const void *a, const void *b) {
  Comparable *ac = (Comparable *)a;
  Comparable *bc = (Comparable *)b;

  if( ac->equals( bc ) )
    return(0);
  else if( ac->greaterthan( bc) )
    return(1);
  else
    return(-1);
}

int main(int argc, char *argv[]) {
  Thing *thing = new Thing[10];

  printf("thing: ");
  for(int i=0;i<10;i++) {
    thing[i].set( random() % 100 );
    printf("%d ", thing[i].get());
  }
  printf("\n");

  // ComparableSort will work for any class inheriting it
  qsort( thing, 10, sizeof(Thing), ComparableSort );

  printf("thing: ");
  for(int i=0;i<10;i++) {
    printf("%d ", thing[i].get());
  }
  printf("\n");

  delete[] thing;

  Thing2 *thing2 = new Thing2[10];

  printf("thing2: ");
  for(int i=0;i<10;i++) {
    thing[i].set( random() % 26 + 'a' );
    printf("%c ", thing[i].get());
  }
  printf("\n");

  // ComparableSort will work for any class inheriting it
  qsort( thing2, 10, sizeof(Thing2), ComparableSort );

  printf("thing2: ");
  for(int i=0;i<10;i++) {
    printf("%c ", thing[i].get());
  }
  printf("\n");
  

  return(0);
}