Object-oriented Software in Ada 95

Arrays 109
8.4.1 The class Board
The specification for the class Board is defined by the package Class_board as follows:
package Class_Board is
type Board is private;
type Game_State is ( Win, Playable, Draw );
procedure Add( The:in out Board; Pos:in Integer;
Piece:in Character );
function Valid( The:in Board; Pos:in Integer ) return Boolean;
function State( The:in Board ) return Game_State;
function Cell( The:in Board; Pos:in Integer )
return Character;
procedure Reset( The:in out Board );
-- Not a concern of the client
end Class_Board;
8.4.2 Implementation of the game
Using the above package specification, the following code will facilitate the playing the game of noughts and
crosses between two human players. The procedure Display will display the state of the board onto the user’s
terminal. By factoring out the code to display the board, from the class Board the class can be re-used in other
programs that may use a different form of display, for example a GUI (Graphical User Interface).
with Class_Board, Ada.Text_Io, Ada.Integer_Text_Io, Display;
use Class_Board, Ada.Text_Io, Ada.Integer_Text_Io;
procedure Main is
Player : Character; --Either 'X' or 'O'
Game : Board; --An instance of Class Board
Move : Integer; --Move from user
begin
Player := 'X';
--Set player
while State( Game ) = Playable loop --While playable
Put( Player & " enter move (1-9) : "); -- move
Get( Move ); Skip_Line; -- Get move
if Valid( Game, Move ) then --Valid
Add( Game, Move, Player ); -- Add to board
Display( Game );
-- Display board
case State( Game ) is --Game is
when Win =>
Put( Player & " wins");
when Playable =>
case Player is --Next player
when 'X' => Player := 'O'; -- 'X' => 'O'
when 'O' => Player := 'X'; -- 'O' => 'X'
when others => null; --
end case;
when Draw =>
Put( "It's a draw ");
end case;
New_Line;
else
Put("Move invalid"); New_Line;
end if;
end loop;
New_Line(2);
end Main;
--for board
© M A Smith - May not be reproduced without permission