type
  TCalc = class
  public
    //out clears the argument on entry,
    //var would keep its value
    procedure GetSum(out Sum: Integer;
      N1, N2: Integer);
  end;

procedure TCalc.GetSum(out Sum: Integer;
  N1, N2: Integer);
begin
  Sum := N1 + N2;
end;

var
  Calc: TCalc;
  Sum: Integer;
begin
  Calc := TCalc.Create;

  Sum := 100;
  Calc.GetSum(Sum, 5, 3);
  //Sum is 8

  WriteLn(Sum);
end.