Task: 21 game


C++: 

#include <cstdlib>
#include <ctime>
#include <iostream>
#include <iomanip>
#include <limits>

using namespace std;
#define _(STR) STR


class Model
{
public:
    static const int GOAL = 21;
    static const int NUMBER_OF_PLAYERS = 2;
    static const int MIN_MOVE = 1;
    static const int MAX_MOVE = 3;
    int bestMove();
    bool update(const char* player, int move);
    bool isGameBegin();
    bool isGameOver();
protected:
    friend class View;
    View* view = nullptr;
    const char* player = nullptr;
    int oldTotal = 0;
    int newTotal = 0;
    int lastMove = 0;
};


class View
{
protected:
    Model* model;
public:
    View(Model* model);
    void init(const char* player);
    void update();
};


class Controller
{
protected:
    Model* model;
    View* view;
public:
    Controller(Model* model, View* view);
    int input();
    void clear();
    void run();
};


int Model::bestMove()
{
    
    

    int move = MIN_MOVE;
    for (int i = MIN_MOVE; i <= MAX_MOVE; i++)
        if ((newTotal + i - 1) % (MAX_MOVE + 1) == 0)
            move = i;
    for (int i = MIN_MOVE; i <= MAX_MOVE; i++)
        if (newTotal + i == GOAL)
            move = i;
    return move;
}

bool Model::update(const char* player, int move)
{
    if (move >= MIN_MOVE && move <= MAX_MOVE && newTotal + move <= GOAL)
    {
        this->player = player;
        oldTotal = newTotal;
        newTotal = oldTotal + move;
        lastMove = move;
        view->update();
        return true;
    }
    else
        return false;
}

bool Model::isGameBegin()
{
    return oldTotal == 0;
}

bool Model::isGameOver()
{
    return newTotal == GOAL;
}


View::View(Model* model)
{
    this->model = model;
    model->view = this;
}

void View::init(const char* player)
{
    if (model->newTotal == 0)
        cout << _("----NEW GAME----\n\n")
             << _("The running total is currently zero.\n")
             << _("The first move is ") << player << _(" move.\n\n");
}

void View::update()
{
    cout << setw(8) << model->player << ": " << model->newTotal << " = "
         << model->oldTotal << " + " << model->lastMove << endl << endl;
    if (model->isGameOver())
        cout << endl << _("The winner is ") << model->player << _(".\n\n\n");
}


Controller::Controller(Model* model, View* view)
{
    this->model = model;
    this->view = view;
}

void Controller::run()
{
    if (rand() % Model::NUMBER_OF_PLAYERS == 0)
    {
        view->init("AI");
        model->update("AI", model->bestMove());
    }
    else
        view->init("human");

    while (!model->isGameOver())
    {
        while (!model->update("human", input()))
            clear();
        model->update("AI", model->bestMove());
    }
}

int Controller::input()
{
    int value;
    cout << _("enter a valid number to play (or enter 0 to exit game): ");
    cin >> value;
    cout << endl;
    if (!cin.fail())
    {
        if (value == 0)
            exit(EXIT_SUCCESS);
        else
            return value;
    }
    else
        return model->MIN_MOVE - 1;
}

void Controller::clear()
{
    cout << _("Your answer is not a valid choice.") << endl;
    cin.clear();
    cin.ignore((streamsize)numeric_limits<int>::max, '\n');
}


int main(int argc, char* argv)
{
    srand(time(NULL));

    cout << _(
        "21 Game                                                          \n"
        "                                                                 \n"
        "21 is a two player game, the game is played by choosing a number \n"
        "(1, 2, or 3) to be added to the running total. The game is won by\n"
        "the player whose chosen number causes the running total to reach \n"
        "exactly 21. The running total starts at zero.                    \n\n");

    while (true)
    {
        Model* model = new Model();
        View* view = new View(model);
        Controller* controler = new  Controller(model, view);

        controler->run();

        delete controler;
        delete model;
        delete view;
    }
    return EXIT_SUCCESS; 
}










Ada: with Ada.Text_IO;
with Ada.Numerics.Discrete_Random;

procedure Game_21 is

   procedure Put (Item : String) is
   begin
      for Char of Item loop
         Ada.Text_IO.Put (Char);
         delay 0.010;
      end loop;
   end Put;

   procedure New_Line is
   begin
      Ada.Text_IO.New_Line;
   end New_Line;

   procedure Put_Line (Item : String) is
   begin
      Put (Item);
      New_Line;
   end Put_LIne;

   type Player_Kind is (Human, Computer);
   type Score_Type  is range 0 .. 21;
   subtype Amount_Range is Score_Type range 1 .. 3;

   package Amount_Generators is
     new Ada.Numerics.Discrete_Random (Amount_Range);

   Gen    : Amount_Generators.Generator;
   Total  : Score_Type := 0;
   Choice : Character;
   Player : Player_Kind;
   Amount : Amount_Range;
begin
   Amount_Generators.Reset (Gen);

   Put_Line ("

   Put ("Who is starting human or computer (h/c) ? ");
   Ada.Text_IO.Get_Immediate (Choice);
   New_Line;

   case Choice is
      when 'c' | 'C' =>  Player := Computer;
      when 'h' | 'H' =>  Player := Human;
      when others => return;
   end case;

   Play_Loop : loop
      New_Line;
      Put ("Runing total is "); Put (Total'Image); New_Line;
      New_Line;

      case Player is

         when Human =>
            Put_Line ("It is your turn !");
            Input_Loop : loop
               Put ("Enter choice 1 .. 3 (0 to end) : ");
               Ada.Text_IO.Get_Immediate (Choice);

               case Choice is
                  when '1' .. '3' =>
                     Amount := Amount_Range'Value ("" & Choice);
                     exit Input_Loop;

                  when '0' =>
                     exit Play_Loop;

                  when others =>
                     Put_Line ("Choice must be in 1 .. 3");
               end case;
            end loop Input_Loop;
            New_Line;

         when Computer =>
            delay 1.500;
            Amount := Amount_Generators.Random (Gen);
            Put ("Computer chooses: "); Put (Amount'Image); New_Line;
            delay 0.800;

      end case;

      New_Line;
      Amount := Score_Type'Min (Amount, Score_Type'Last - Total);
      Put ("  "); Put (Total'Image); Put (" + ");  Put (Amount'Image); Put (" = ");
      Total := Total + Amount;
      Put (Total'Image);
      New_Line;

      if Total = 21 then
         New_Line;
         Put ("... and we have a WINNER !!"); New_Line;
         delay 0.500;
         Put_Line ("   ... and the winner is ...");
         delay 1.000;
         Put_Line ("      " & Player'Image);
         exit;
      end if;

      Player := (case Player is
                 when Computer => Human,
                 when Human    => Computer);
   end loop Play_Loop;
end Game_21;