Обособяване на класове
Чете се информация за компютри, съдържаща:

OmniBook XE
5660
76
ACMA P300
1095
75
AMAX Poewrstation
1999
78

Търси се продукта с най-голямо отношение оценка/цена.

#include <iostream>
#include <string>
using namespace std;

int main()
{  string best_name = "";
   double best_price = 0;
   int best_score = 0;

   bool more = true;
   while (more)
   {  string next_name;
      double next_price;
      int next_score;

      cout << "Please enter the model name: ";
      getline(cin, next_name);
      cout << "Please enter the price: ";
      cin >> next_price;
      cout << "Please enter the score: ";
      cin >> next_score;
      string remainder; /* read remainder of line */
      getline(cin, remainder);

      if (next_price != 0)
      {  if (best_price == 0 or
            next_score/next_price > best_score/best_price)
         {  best_name = next_name;
            best_score = next_score;
            best_price = next_price;
         }
      }
      cout << "More data? (y/n) ";
      string answer;
      getline(cin, answer);
      if (answer != "y") more = false;
   }
   cout << "The best bang for the buck is " << best_name
      << " (Score: " << best_score
      << " Price: " << best_price << ")\n";
   return 0;
}

Интерфейс и капсулиране
#include <iostream>
#include <string>
using namespace std;

class Product  {
public:   /*интерфейс*/     
   Product();                    /*създава нов продукт*/
   void read();                         /*чете продукт*/
   bool is_better_than(Product b) const;    /*сравнява*/
   void print() const;                     /*отпечатва*/
private:  /*капсулиране*/
   string name;                         /*скрити данни*/
   double price;                        /*скрити данни*/
   int score;                           /*скрити данни*/
};

int main()
{  Product best;

   bool more = true;
   while (more)
   {  Product next;
      next.read();
      if (next.is_better_than(best)) best = next;

      cout << "More data? (y/n) ";
      string answer;
      getline(cin, answer);
      if (answer != "y") more = false;
   }
   cout << "The best bang for the buck is ";
   best.print();
   return 0;
}

Членове-функции
* конструктор
Product::Product() {  price = 10000;   score = 0; }

* мутатори (set-функции)
void Product::read()
{  cout << "Please enter the model name: ";
   getline(cin, name);
   cout << "Please enter the price: ";
   cin >> price;
   cout << "Please enter the score: ";
   cin >> score;
   string remainder;
   getline(cin, remainder); }

* функции за достъп (get-функции)
bool Product::is_better_than(Product b) const
{  if (price == 0) return false;
    if (b.price == 0) return true;
    if (score/price > b.score/b.price) return true;
    return false;   }

void Product::print() const
{  cout << name
        << " Price: " << price
        << " Score: " << score << "\n";  }
* Неявен параметър на член-функция
set-функции - променят неявния си параметър
get-функции - не променят неявния си параметър, използване на const

Конструктори по подразбиране и с параметри
* Конструкторът инициализира полетата (членовете) данни на обекта
* Предефиниране на функции
class Employee {
public:
   Employee();
   Employee(string emp_name, double init_salary);
   void set_salary(double new_salary);
   string get_name() const;
   double get_salary() const;
   void print() const;
private:
   string name;
   double salary;
};

Employee::Employee(string emp_name, double init_salary)
{ name = emp_name;
  salary = init_salary;  }

* Полета с данни - обекти от други класове
class Employee {
public: 
   Employee(string emp_name, double init_salary,
            int arrive_hour, int leave_hour);
   ...
private:
   string name;
   double salary;
   Time arrive;
   Time leave;
};

Employee(string emp_name, double init_salary,
            int arrive_hour, int leave_hour)
{ name = emp_name;
  salary = init_salary;
  arrive = Time(arrive_hour, 0, 0);
  leave = Time(leave_hour, 0, 0);
}

Достъп до полетата с данни
 * Само членовете-функции имат достъп до скритите полета с данни
   string get_name() const   { return name; }

   double get_salary() const { return salary; }

* Явни и неявни параметри на функции
-- член-функция с използване на достъпът до скритите данни
void Employee::print() const
{ cout << "Name: " << name << "    "
       << "Salary: " << salary << "\n"; }
-- член-функция с използване на член-функции от същия клас
void Employee::print() const
{ cout << "Name: " << get_name() << "    "
       << "Salary: " << get_salary() << "\n"; }
-- външна за класа функция
void print(Employee const &emp)
{ cout << "Name: " << emp.get_name() << "    "
       << "Salary: " << emp.get_salary() << "\n"; }
Принципи на обектно-ориентираното програмиране

* Определяне на интерфейс
Игра, която обучава децата да познават часовника.
 

** Клас Clock:
class Clock  {
public:
   Clock();
   Clock(Point c, double r);
   void set_time(Time t);
   void draw() const;
private:
   Time current_time;
   Point center;
   double radius;
};

void Clock::set_time(Time t)
{  current_time = t;  }

Рисуване на часовник:
- рисуване на кръг
- рисуване на часовите деления
- рисуване на минутните деления
- рисуване на часовата стрелка
- рисуване на минутната стрелка

Рисува часово или минутно деление:
void Clock::draw_tick(double angle, double length) const
{  double alpha = PI/2 - 6*angle*PI/180;
   Point from(center.get_x() + cos(alpha)*radius*(1-length),
              center.get_y() + sin(alpha)*radius*(1-length));
   Point to(center.get_x() + cos(alpha)*radius,
            center.get_y() + sin(alpha)*radius);
   cwin << Line(from, to);
}
Рисува стрелка:
void Clock::draw_hand(double angle, double length) const
{  double alpha = PI/2 - 6*angle*PI/180;
   Point from = center;
   Point to(center.get_x() + cos(alpha)*radius*length,
            center.get_y() + sin(alpha)*radius*length);
   cwin << Line(from, to);
}
Рисува циферблат:
void Clock::draw() const
{  cwin << Circle(center, radius);
   int i;
   const double HOUR_TICK_LENGTH = 0.2;
   const double MINUTE_TICK_LENGTH = 0.1;
   const double HOUR_HAND_LENGTH = 0.6;
   const double MINUTE_HAND_LENGTH = 0.75;
   for (i = 0; i < 12; i++)
   {  draw_tick(i * 5, HOUR_TICK_LENGTH);
      int j;
      for (j = 1; j <= 4; j++)
         draw_tick(i * 5 + j, MINUTE_TICK_LENGTH);
   }
   draw_hand(current_time.get_minutes(), MINUTE_HAND_LENGTH);
   draw_hand((current_time.get_hours() +
      current_time.get_minutes() / 60.0) * 5, HOUR_HAND_LENGTH);
}
** Ще използваме готовия клас Time.
** Клас Player:
class Player  {
public:
   Player();
   Player(string player_name, int initial_level);

   void increment_score();
   int get_level() const;
   string get_name() const;
private:
   string name;
   int score;
   int level;
};

Player::Player(string player_name, int initial_level)
{  name = player_name;
   level = initial_level;
   score = 0;
}
int Player::get_level() const   { return level; }

string Player::get_name() const {  return name; }

void Player::increment_score()
{  score++;
   if (score % 5 == 0 and level < 4) level++;
}
** Клас Game:
class Game {
public:
   Game();
   void play();
   void read_player_information();
   void play_round();
private:
   Player player;
};

Game::Game() {  rand_seed();  }

void Game::play()
{ read_player_information();
  string response;
  do
  { play_round();
    response = cwin.get_string("Do you want to play again? (y/n)");
  } while (response == "y");
}

void Game::read_player_information()
{  string name = cwin.get_string("What is your name?");
   int initial_level;
   do
   { initial_level =
     cwin.get_int("At what level do you want to start? (1-4)");
   } while (initial_level < 1 or initial_level > 4);
   player = Player(name, initial_level);
}
Изиграване на кръг:
- генериране на случайно време
- показване на времето
- получаване на отговор
- ако отговорът не е правилен, отново получаване на отговор
- ако отговорът е правилен - поздравления и увеличаване на точките

Генериране на случайно време:
Time Game::random_time()
{  int level = player.get_level();
   int minutes;
   if (level == 1) minutes = 0;
   else if (level == 2) minutes = 15 * rand_int(0, 3);
   else if (level == 3) minutes = 5 * rand_int(0, 11);
   else minutes = rand_int(0, 59);
   int hours = rand_int(1, 12);
   return Time(hours, minutes, 0);
}
Получаване на отговор:
Time Game::get_guess()
{  int hours;
   do
   {  hours = cwin.get_int("Please enter hours: (1-12)");
   } while (hours < 1 or hours > 12);
   int minutes;
   do
   {  minutes = cwin.get_int("Please enter minutes: (0-59)");
   } while (minutes < 0 or minutes > 59);

   return Time(hours, minutes, 0);
}
Изиграване на кръг:
void Game::play_round()
{  cwin.clear();
   Time t = random_time();
   const double CLOCK_RADIUS = 5;
   Clock clock(Point(0, 0), CLOCK_RADIUS);
   clock.set_time(t);
   clock.draw();

   Time guess = get_guess();
   if (t.seconds_from(guess) != 0) guess = get_guess();

   string text;
   if (t.seconds_from(guess) == 0)
   {  text = "Congratulations, " + player.get_name()
         + "! That is correct.";
      player.increment_score();
   }
   else
      text = "Sorry, " + player.get_name()
         + "! That is not correct.";
   cwin << Message(Point(-CLOCK_RADIUS, CLOCK_RADIUS + 1),text);
}
** Главна програма:
int main()
{  Game clock_game;
   clock_game.play();
   return 0;
}
** Цялата програма:
#include "ccc_win.cpp"
#include "ccc_time.cpp"

const double PI = 3.141592653589793;

class Clock  {
public:
   Clock();
   Clock(Point c, double r);

   void set_time(Time t);
   void draw() const;
private:
   void draw_tick(double angle, double length) const;
   void draw_hand(double angle, double length) const;

   Time current_time;
   Point center;
   double radius;
};

class Player  {
public:
   Player();
   Player(string player_name, int initial_level);

   void increment_score();
   int get_level() const;
   string get_name() const;
private:
   string name;
   int score;
   int level;
};

class Game  {
public:
   Game();
   void play();
   void read_player_information();
   void play_round();
   Time random_time();
   Time get_guess();
private:
   Player player;
};

void rand_seed()
/* PURPOSE: Set the seed of the random number generator
*/
{  int seed = static_cast<int>(time(0));
   srand(seed);
}

int rand_int(int a, int b)
/* PURPOSE:  Return a random integer in a range
   RECEIVES: a - the bottom of the range
             b - the top of the range
   RETURNS:  A random number x, a <= x and x <= b
*/
{  return a + rand() % (b - a + 1); }

Clock::Clock(){}

Clock::Clock(Point c, double r)
/* RECEIVES:  c - the center of the clock
              r - the radius of the clock
*/
{  center = c;   radius = r;  }

void Clock::set_time(Time t)
/* PURPOSE:  set the current time
   RECEIVES: t - the time to set
*/
{  current_time = t;  }

void Clock::draw_tick(double angle, double length) const
/* PURPOSE:  draw a tick mark (hour or minute mark)
   RECEIVES: angle - the angle in minutes (0...59, 0 = top)
             length - the length of the tick mark
*/
{  double alpha = PI / 2 - 6 * angle * PI / 180;
   Point from(center.get_x() + cos(alpha) * radius * (1 - length),
      center.get_y() + sin(alpha) * radius * (1 - length));
   Point to(center.get_x() + cos(alpha) * radius,
      center.get_y() + sin(alpha) * radius);
   cwin << Line(from, to);
}

void Clock::draw_hand(double angle, double length) const
/* PURPOSE:  draw a hand, starting from the center
   RECEIVES: angle - the angle in minutes (0...59, 0 = top)
             length - the length of the hand
*/
{  double alpha = PI / 2 - 6 * angle * PI / 180;
   Point from = center;
   Point to(center.get_x() + cos(alpha) * radius * length,
      center.get_y() + sin(alpha) * radius * length);
   cwin << Line(from, to);
}

void Clock::draw() const
/* PURPOSE:  draw the clock, with tick marks and hands
*/
{  cwin << Circle(center, radius);
   int i;
   const double HOUR_TICK_LENGTH = 0.2;
   const double MINUTE_TICK_LENGTH = 0.1;
   const double HOUR_HAND_LENGTH = 0.6;
   const double MINUTE_HAND_LENGTH = 0.75;
   for (i = 0; i < 12; i++)
   {  draw_tick(i * 5, HOUR_TICK_LENGTH);
      int j;
      for (j = 1; j <= 4; j++)
         draw_tick(i * 5 + j, MINUTE_TICK_LENGTH);
   }
   draw_hand(current_time.get_minutes(), MINUTE_HAND_LENGTH);
   draw_hand((current_time.get_hours() +
      current_time.get_minutes() / 60.0) * 5, HOUR_HAND_LENGTH);
}

Player::Player()
{  level = 1;   score = 0;  }

Player::Player(string player_name, int initial_level)
/* RECEIVES: player_name - the player name
             initial_level - the player's level (1...4)
*/
{  name = player_name;
   level = initial_level;
   score = 0;
}

int Player::get_level() const
{  return level;  }

string Player::get_name() const
{  return name;  }

void Player::increment_score()
/* PURPOSE:  increment score
   REMARKS:  moves to next level if current level complete
*/
{  score++;
   if (score % 5 == 0 and level < 4) level++;
}

Game::Game(){  rand_seed();  }

void Game::play()
/* PURPOSE:  plays the game while the player wants to continue
*/
{  read_player_information();
   string response;
   do
   {  play_round();
      response = cwin.get_string("Do you want to play again? (y/n)");
   } while (response == "y");
}

void Game::read_player_information()
/* PURPOSE:  reads player name and level
*/
{  string name = cwin.get_string("What is your name?");
   int initial_level;
   do
   {  initial_level =
         cwin.get_int("At what level do you want to start? (1-4)");
   } while (initial_level < 1 or initial_level > 4);
   player = Player(name, initial_level);
}

Time Game::random_time()
/* PURPOSE:  make a random time, depending on the level
   RETURNS:  the random time
*/
{  int level = player.get_level();
   int minutes;
   if (level == 1) minutes = 0;
   else if (level == 2) minutes = 15 * rand_int(0, 3);
   else if (level == 3) minutes = 5 * rand_int(0, 11);
   else minutes = rand_int(0, 59);
   int hours = rand_int(1, 12);
   return Time(hours, minutes, 0);
}

Time Game::get_guess()
/* PURPOSE:  get a time input from the user
   RETURNS:  the time guessed by the user
*/
{  int hours;
   do
   {  hours = cwin.get_int("Please enter hours: (1-12)");
   } while (hours < 1 or hours > 12);
   int minutes;
   do
   {  minutes = cwin.get_int("Please enter minutes: (0-59)");
   } while (minutes < 0 or minutes > 59);

   return Time(hours, minutes, 0);
}

void Game::play_round()
/* PURPOSE:  Play a round, with up to two guesses
*/
{  cwin.clear();
   Time t = random_time();
   const double CLOCK_RADIUS = 5;
   Clock clock(Point(0, 0), CLOCK_RADIUS);
   clock.set_time(t);
   clock.draw();

   Time guess = get_guess();
   if (t.seconds_from(guess) != 0)
      guess = get_guess();

   string text;
   if (t.seconds_from(guess) == 0)
   {  text = "Congratulations, " + player.get_name()
         + "! That is correct.";
      player.increment_score();
   }
   else
      text = "Sorry, " + player.get_name()
         + "! That is not correct.";
   cwin << Message(Point(-CLOCK_RADIUS, CLOCK_RADIUS + 1), text);
}

int main()
{  Game clock_game;
   clock_game.play();

   return 0;
}