Object-oriented Software in Ada 95

112 Arrays
The functions valid returns true if the square selected is not occupied by a previously played counter.
function Valid(The:in Board; Pos:in Integer) return Boolean is
begin
return Pos in Board_Array'Range and then
The.Sqrs( Pos ) = ' ';
end Valid;
Note:
The use of and then so that the check on the board is only made if the position is valid.
The function Cell returns the contents of a cell on the noughts and crosses board. This method is used to
interrogate the state of the board, without having to know how the state is stored. Using this method, printing of
the state of the board can be separated from the code that manipulates the board.
function Cell(The:in Board; Pos:in Integer) return Character is
begin
return The.Sqrs( Pos );
end Cell;
The procedure Reset sets the state of the board back to its initial state.
procedure Reset( The:in out Board ) is
begin
The.Sqrs := ( others => ' '); --All spaces
The.Moves := 0; --No of moves
end Reset;
The Procedure State returns the current state of play as represented by the board. A two-dimensional array
All_Win_Lines holds the co-ordinates of the eight possibles win lines. The co-ordinates in this array are used
to find any line that contains three cells either containing all X’s or O’s.
function State( The:in Board ) return Game_State is
subtype Position is Integer range 1 .. 9;
type Win_Line is array( 1 .. 3 ) of Position;
type All_Win_Lines is range 1 .. 8;
Cells: constant array ( All_Win_Lines ) of Win_Line :=
( (1,2,3), (4,5,6), (7,8,9), (1,4,7),
(2,5,8), (3,6,9), (1,5,9), (3,5,7) ); --All win lines
First : Character;
begin
for Pwl in All_Win_Lines loop --All Pos Win Lines
First := The.Sqrs( Cells(Pwl)(1) ); --First cell in line
if First /= ' ' then -- Looks promising
if First = The.Sqrs(Cells(Pwl)(2)) and then
First = The.Sqrs(Cells(Pwl)(3)) then
return Win;
-- Found a win
end if;
end if;
end loop;
if The.Moves >= 9 then --Check for draw
return Draw;
-- Board full so draw
else
return Playable;
-- Still playable
end if;
end State;
end Class_Board;
© M A Smith - May not be reproduced without permission