-- Chapter 21 - Programming exercise 2

-- This package uses a data structure composed of three INTEGER
-- variables.  It allow the user to add two structures, component
-- by component, or subtract component by component.  Provision is
-- also made to build a structure from three numbers, or decompose
-- a structure into its components.

package Three is
type DATA_STRUCTURE is private;
function "+"(Data1, Data2 : DATA_STRUCTURE) return DATA_STRUCTURE;
function "-"(Data1, Data2 : DATA_STRUCTURE) return DATA_STRUCTURE;
function Build_Structure(Val1, Val2, Val3 : INTEGER) return
                                                   DATA_STRUCTURE;
procedure Decompose(Data1 : DATA_STRUCTURE;
                    Val1, Val2, Val3 : out INTEGER);
function Compare_Sum(Data1, Data2 : DATA_STRUCTURE) return BOOLEAN;

private
   type DATA_STRUCTURE is array(1..3) of INTEGER;
end Three;



package body Three is

function "+"(Data1, Data2 : DATA_STRUCTURE) return DATA_STRUCTURE is
Temp : DATA_STRUCTURE;
begin
   Temp(1) := Data1(1) + Data2(1);
   Temp(2) := Data1(2) + Data2(2);
   Temp(3) := Data1(3) + Data2(3);
   return Temp;
end "+";


function "-"(Data1, Data2 : DATA_STRUCTURE) return DATA_STRUCTURE is
Temp : DATA_STRUCTURE;
begin
   Temp(1) := Data1(1) - Data2(1);
   Temp(2) := Data1(2) - Data2(2);
   Temp(3) := Data1(3) - Data2(3);
   return Temp;
end "-";


function Build_Structure(Val1, Val2, Val3 : INTEGER) return
                                                   DATA_STRUCTURE is
Temp : DATA_STRUCTURE;
begin
   Temp(1) := Val1;
   Temp(2) := Val2;
   Temp(3) := Val3;
   return Temp;
end Build_Structure;


procedure Decompose(Data1 : DATA_STRUCTURE;
                    Val1, Val2, Val3 : out INTEGER) is
begin
   Val1 := Data1(1);
   Val2 := Data1(2);
   Val3 := Data1(3);
end Decompose;


function Compare_Sum(Data1, Data2 : DATA_STRUCTURE)
                                                 return BOOLEAN is
begin
   return (Data1(1) + Data1(2) + Data1(3)) =
                                  (Data2(1) + Data2(2) + Data2(3));
end Compare_Sum;

end Three;




-- This program exercises the package Three as an illustration.

with Ada.Text_IO;  use Ada.Text_IO;
with Three;        use Three;

procedure CH21_2 is

   My_Data, Extra_Data : DATA_STRUCTURE;
   Temp                : DATA_STRUCTURE;

begin

   My_Data := Build_Structure(3,7,13);
   Extra_Data := Build_Structure(-4,77,0);
   My_Data := My_Data + Extra_Data;

   if My_Data /= Extra_Data then
      Put_Line("The two structures are not equal.");
   end if;

   My_Data := Extra_Data;

   if My_Data = Extra_Data then
      Put_Line("The two structures are equal now.");
   end if;

--       The following line is illegal with the private type.
-- My_Data.Value1 := My_Data.Value1 + 13;

   Temp := Build_Structure(13,0,0);
   My_Data := My_Data + Temp;

   if not Compare_Sum(My_Data, Temp) then
      Put_Line("My_Data and Temp are not equal.");
   end if;

   My_Data := Build_Structure(1,9,3);
   if Compare_Sum(My_Data, Temp) then
      Put_Line("My_Data and Temp are equal.");
   end if;

end CH21_2;




-- Result of execution

-- The two structures are not equal.
-- The two structures are equal now.
-- My_Data and Temp are not equal.
-- My_Data and Temp are equal.