Pascal the Snake

program Snake;
uses Crt;

type
        SnakeCell = record
                xCoord: Integer;
                yCoord: Integer;
        End;

label wrongDirection;

const
        up = 1;
        down = 2;
        left = 3;
        right = 4;

        lines = 15; {number of lines}
        rows = 20; {number of rows}

        {number of lines and rows can be changed without any restriction
        except the limits of the map[][]}

        empty = 0;         //' '
        wall = 1;          //#
        food = 2;          //@
        clear = -1;

        snakeHead = 10; //O
        snakeBody = 11; //x

var
        i, j, h, t, k : integer;
        map: Array[1..25,1..80] of Integer;
        isRunning : boolean;
        snakeA: Array[1..200] of SnakeCell;
        direction: integer;
        foodX, foodY: integer;
        isFood: boolean;
        points: integer;

        key : char;
begin


ClrScr;
isFood := false;
Randomize;
points := 0;

for i:=2 to 200 do begin
        snakeA[i].xCoord := -1;
        snakeA[i].yCoord := -1;
end;

{this is positioning the snake in the middle of the map}

snakeA[1].xCoord := rows div 2;
snakeA[1].yCoord := lines div 2;

{this is creating the game map}
for i:=1 to lines do begin
        for j:=1 to rows do begin
                if (i=1) OR (j = 1) OR (i = lines) OR (j = rows) then map[i][j]:=1
                else map[i][j] := 0;
         end;
end;

{this prints the walls and leaves the inside space empty}

for i:=1 to lines do begin
        for j:=1 to rows do begin
                if map[i][j] = wall then write('#')
                else if map[i][j] = empty then write(' ');
        end;
        writeln();

end;


isRunning := true; {variable which will keep the game-loop running}

{bringing Pascal to life }

gotoxy(snakeA[1].xCoord, snakeA[1].yCoord);
write ('O');

repeat                                 {game loop}

        wrongDirection:      {this is a label for GOTO}

        if isFood = false then begin       {if there is no food, create one}
                foodX := random(rows-2) + 2;
                foodY := random(lines-2) + 2;
                isFood := true;
                gotoxy(foodX, foodY);
                write ('@');
        end;

        {if a key is pressed, check if the snake can do that move
        (the direction doesn't change by 180 degrees) and if it is ok
        then change the direction}

        if Keypressed then begin
                key := readkey;

                case key of
                        #75 : begin if direction = right then goto wrongDirection; direction := left; end;
                        #72 : begin if direction = down then goto wrongDirection; direction := up; end;
                        #77 : begin if direction = left then goto wrongDirection; direction := right; end;
                        #80 : begin if direction = up then goto wrongDirection; direction := down; end;
                        #27 : break;
                end;
        end;

        {erase the snake so it can be painted to the next position}

                gotoxy(snakeA[1].xCoord, snakeA[1].yCoord); write(' ');
                for t:=2 to 200 do begin
                        if snakeA[t].xCoord <> -1 then begin
                                gotoxy(snakeA[t].xCoord, snakeA[t].yCoord);
                                write(' ');
                        end
                        else break;
                end;

                {compute the movement of each snake cell
                the for must go from 200 down , otherwise all the cells would
                be stacked up on the snakeA[2] position}

                {each cell will move where the one before it was}

                for j:=200 downto 2 do begin
                        if snakeA[j].xCoord <> - 1 then begin
                                snakeA[j].xCoord := snakeA[j-1].xCoord;
                                snakeA[j].yCoord := snakeA[j-1].yCoord;
                                end;
                end;

                {this is the movement of the Snake Head}

                case direction of
                        up : snakeA[1].yCoord := snakeA[1].yCoord - 1;
                        down : snakeA[1].yCoord := snakeA[1].yCoord + 1;
                        left : snakeA[1].xCoord := snakeA[1].xCoord - 1;
                        right : snakeA[1].xCoord := snakeA[1].xCoord + 1;
                end;

                {display the snake at its new position}

                gotoxy(snakeA[1].xCoord, snakeA[1].yCoord); write('O');
                for i:=2 to 200 do begin
                        if snakeA[i].xCoord <> -1 then begin gotoxy(snakeA[i].xCoord,snakeA[i].yCoord);write('x');
                        end
                        else break;
                end;

                {check if the snakehead collided with any of its cells}

                for k:=2 to 200 do begin
                        if snakeA[k].xCoord = -1 then break;
                        if (snakeA[k].xCoord = snakeA[1].xCoord) and (snakeA[k].yCoord = snakeA[1].yCoord) then isRunning := false;
                end;

                {if the snake collided with the food we consider to have eaten it
                so: *there is no food on the screen anymore
                *the user gains one point
                *we find the first position in the array that isn't used and
                add a cell to the current snake}

                if (snakeA[1].yCoord = foodY) and (snakeA[1].xCoord = foodX) then begin
                        isFood := false;
                        points := points+1;
                        for h:=2 to 200 do begin
                                if snakeA[h].xCoord = -1 then begin snakeA[h].xCoord := snakeA[h-1].xCoord; snakeA[h].yCoord :=snakeA[h-1].yCoord;break;end;

                        end;
                end;

                {delay(150) makes the snake move reasonably fast but not too fast}

                delay(150);
                gotoxy(1, lines+1); write('Points: ', points);  //points are displayed

                {if the snakehead collided with a wall , the game is over}

                if (snakeA[1].xCoord<=1) or (snakeA[1].yCoord<=1) or (snakeA[1].xCoord >= rows) or (snakeA[1].yCoord>=lines) then isRunning := false;


        until isRunning = false;

        {the screen will be paused a little after the game was ended so the
        player can see the points}

        delay(3000);


end.     {THE END}