procedure TMainForm.btnBuildClick(Sender: TObject);
var
   I: Integer;
begin
   Tree := TBTree.Create;
   SetLength(Arr, StrToInt(edtA.Text));
   if not CheckIfNonDescendingAndCorrectSG(sgA) then
   begin
      MessageBox(0, PChar('List A must be NONdecreasing'), PChar('Warning!'),
        MB_ICONERROR);
      Exit;
   end;
   with sgA do
   begin
      for I := 0 to ColCount - 1 do
         try
            Arr[I] := StrToInt(Cells[I, 0]);
         except
            MessageBox(0, PChar('List shouldn''t contain empty cells.'),
              PChar('Warning!'), MB_ICONERROR);
            Exit;
         end;
   end;
   try
      Tree.BinarySearch(0, Length(Arr) - 1, StrToInt(edtWanted.Text),
        Arr, Tree);
   except
      MessageBox(0, PChar('Wanted value is not correct.'), PChar('Warning!'),
        MB_ICONERROR);
      Exit;
   end;
   fCanvas := TCanvasForm.Create(Self);
   fCanvas.Show;
   DrawTree(MAX_WIDTH div 2, MAX_HEIGHT div Tree.Depth div 2,
     MAX_CANVAS_WIDTH div 2, MAX_HEIGHT div Tree.Depth, RADIUS, Tree,
     fCanvas.Canvas);
   Tree.Destroy;
   Tree := nil;
end;