Задача про шарик отталкивающийся от стенок.

uses GraphABC;
var i,j,e,d,c:integer;
const
k=5;
t=10;
l=200;
procedure upright;
begin
while ((j>k) and (i<(l-k))) do
begin
i:=i+c;
j:=j-d;
clearwindow;
SetPenWidth(1);
SetBrushColor(clBlue);
circle(i,j,k);
sleep(t);
end;
end;
procedure upleft;
begin
while (j>k) and (i>k) do
begin
i:=i-c;
j:=j-d;
clearwindow;
SetPenWidth(1);
SetBrushColor(clBlue);
circle(i,j,k);
sleep(t);
end;
end;
procedure downright;
begin
while (j<(l-k)) and (i<(l-k)) do
begin
i:=i+c;
j:=j+d;
clearwindow;
SetPenWidth(1);
SetBrushColor(clBlue);
circle(i,j,k);
sleep(t);
end;
end;
procedure downleft;
begin
while (j<(l-k)) and (i>k) do
begin
i:=i-c;
j:=j+d;
clearwindow;
SetPenWidth(1);
SetBrushColor(clBlue);
circle(i,j,k);
sleep(t);
end;
end;
begin
SetWindowWidth(l);
SetWindowHeight(l);
j:=Random(l-2*k)+15;
i:=Random(l-2*k)+15;
d:=Random(5)+1;
c:=Random(5)+1;
SetPenWidth(1);
SetBrushColor(clBlue);
circle(i,j,k);
e:=Random(4)+1;
begin
case e of
1:upright;
2:upleft;
3:downright;
4:downleft;
end;
repeat
begin
if e=1 then e:=3 else
if e=2 then e:=4 else
if e=3 then e:=1 else
if e=4 then e:=2;
begin
case e of
1:upright;
2:upleft;
3:downright;
4:downleft;
end;
end;
end;
until e=5;
end;
end.