const
{$ J +}
  num: Integer = 1;
{$ J-}
begin
  Inc (num);
  ShowMessage (IntToStr (num)); {2}
end ;

// or writing:
const
{$ WRITEABLECONST ON}
  num: Integer = 1;
{$ WRITEABLECONST OFF}
begin
  Inc (num);
  ShowMessage (IntToStr (num)); {2}
end ;