Object-oriented Software in Ada 95

Case study: Design of a game 141
The function Find_Turned finds the number of the opponent’s counters that would be turned for a
particular move. The strategy for Find_Turned is to sum the number of opponent's counters which will be
flipped in each compass direction. For any position on the board there are potentially eight directions to check.
The directions are illustrated in Figure 9.5.
7
8
1
6
2
Figure 9.5 Compass direction to check when a new counter is added to the board.
function Find_Turned( The:in Board; X,Y: in Board_Index )
return Natural is
Sum : Natural := 0; --Total stones turned
begin
if Holds( The.Sqrs( X, Y ) ) = Empty then
for Dir in 1 .. 8 loop --The 8 possible directions
Sum := Sum + No_Turned( The, X, Y, Dir );
end loop;
end if;
return Sum; --return total
end Find_Turned;
5
4
3
The recursive function No_Turned counts the number of the opponent’s pieces that would be captured. This
may of course be zero.
function No_Turned(The:in Board; O_X,O_Y:in Board_Index;
Dir:in Natural;
N:in Natural := 0 ) return Natural is
Ok : Boolean;
--Result from next
Nxt: Cell_Holds;
--Next in line is
Col: Counter_Colour;
--Counter colour
X : Board_Index := O_X; --Local copy
Y : Board_Index := O_Y; --Local copy
begin
Next( The, X,Y, Dir, Ok ); --Next cell
if Ok then
--On the board
Nxt := Holds( The.Sqrs(X,Y) ); --Contents are
if Nxt = Empty then --End of line
return 0;
else
Col := To_Colour( Nxt ); --Colour
if Col = The.Opponent then --Opponents counter
return No_Turned(The, X,Y, Dir, N+1); --Try next cell
elsif Col = The.Player then --End of counters
return N;
end if;
end if;
else
return 0;
end if;
end No_Turned;
--Counters turned
--No line
© M A Smith - May not be reproduced without permission