program B_Tree;
Uses Crt, Graph;

Type
  TType = Char;
  PTTree = ^TTree;
  TTree = Record
    Data: TType;
    Left, Right: PTTree;
End;

procedure PrintTreeGraph(root: pttree);

  Function Convert(X: TType): String;
  Begin
    Convert := X;
  End;

  var
    start_x, start_y: integer;

  const
    delx = 30;
    dely = 20;
    circle_r = 10;
    btw = circle_r div 2;

  procedure print_node(T: pttree; level: integer;
            L, C, R: integer);

  function min(a, b: integer): integer;
  begin
    min := a;
    if b < a then min := b
  end;

  function Center(a, b: integer): integer;
  begin
    Center := min( a, B ) + abs( a - B ) div 2;
  end;

  var pos_y: integer;

  begin
    pos_y := start_y + pred(level) * dely;
    if T^.right <> nil then begin
      line(C, pos_y, Center(C, R), pos_y + dely);
      { вот тут мы предотвращаем наложение (уходим чуть вправо) }
      print_node(T^.right, level + 1, C+btw, Center(C+btw, R-btw), R-btw);
    end;

    if T^.left <> nil then begin
      line(C, pos_y, Center(L, C), pos_y + dely);
      { и вот тут тоже (уходим левее) }
      print_node(T^.left, level + 1, L+btw, Center(L+btw, C-btw), C-btw);
    end;

    setcolor(black);
    setfillstyle(solidfill, black);
    pieslice(C, pos_y, 0, 359, circle_r);
    setcolor(white);
    circle(C, pos_y, circle_r);
    settextjustify(centertext, centertext);
    outtextxy(C, pos_y, Convert(t^.data));
  end;

begin
  start_x := getmaxx div 2;
  start_y := 10;
  print_node(root, 1, 0, getmaxx div 2, getmaxx);
end;


function resultat (root:PTTree):real;

  function Encode (data: char): real;
  var x: real;
  begin
    write (data,' = ');
    readln (x);
    encode:= x;
  end;

begin
  if root=nil then exit;
  case root^.data of
    '+': resultat:= resultat(root^.left) + resultat(root^.right);
    '-': resultat:= resultat(root^.left) - resultat(root^.right);
    '*': resultat:= resultat(root^.left) * resultat(root^.right);
    '/': if resultat(root^.right) = 0 then
         begin
            resultat:=0;
            write ('Error');
         end
         else
           resultat:= resultat(root^.left) / resultat(root^.right);
   else
     resultat:= encode (root^.data);
end
end;

var
  global_root: pttree;

Procedure Build(Var root: PTTree;
          Expr: String; Var Shift: Integer);

Begin
  New(root);
  Root^.Data  := Expr[Shift];
  Root^.Left  := nil;
  Root^.Right := nil;
  If (Expr[Shift] in ['+','*','-','/']) Then Begin
    Inc(Shift);
    Build(Root^.Left, Expr, Shift);
    Build(Root^.Right, Expr, Shift);
  End
  Else Inc(Shift)
End;


Const
  i: integer = 1;

Var
  s: string;
  grDriver: integer;
  grMode: integer;
  ErrCode: Integer;

begin
  global_root := nil;
  writeln ('Vvedite virazenie v prefixnoy forme: ');
  readln (s);
  Build(global_root, s, i);
  grDriver := Detect;
  InitGraph(grDriver, grMode,'');
  ErrCode := GraphResult;
  if ErrCode <> grOk then begin
    Writeln('Graphics error:', GraphErrorMsg(ErrCode)); Halt(100);
  end;

  PrintTreeGraph(global_root);
  readln;
  CloseGraph;
  writeln (resultat(global_root):2:3);
  readln;
end.