-- gears.adb: compute for a specific case the gear ratio for each
-- choice of gears on a bicycle, expressed as a rational fraction.
-- From this information the correct gear shifting order can be
-- derived by simply sorting the output of this program on the
-- column containing the speed factor.

-- Kent Paul Dolan's first substantive Ada 95 program, completed
-- September 30th, 1999.

with Ada.Text_IO, Ada.Integer_Text_IO;

procedure Gears is

-- type for telling how many teeth a particular front or back gear has

  subtype Gear_Tooth_Cardinal is integer range 1 .. 100;

-- type for which front gear position is in use

  subtype Front_Gear_Ordinal is integer range 1 .. 3;

  Front_Bottom_Gear: Front_Gear_Ordinal := 1;
  Front_Top_Gear   : Front_Gear_Ordinal := 2;

  Front_Gear_Teeth: array ( Front_Bottom_Gear .. Front_Top_Gear )
    of Gear_Tooth_Cardinal := ( 39 , 50 );

-- type for which back gear position is in use

  subtype Back_Gear_Ordinal is integer range 1 .. 7;

  Back_Bottom_Gear: Back_Gear_Ordinal := 1;
  Back_Top_Gear   : Back_Gear_Ordinal := 5;

  Back_Gear_Teeth:  array ( Back_Bottom_Gear .. Back_Top_Gear )
    of Gear_Tooth_Cardinal := ( 28, 24, 20, 17, 14 );

  Gear_Ratio_Base : Integer := 1;

begin

  for Back_Gear_Position in Back_Bottom_Gear .. Back_Top_Gear loop
    Gear_Ratio_Base := Gear_Ratio_Base * Back_Gear_Teeth( Back_Gear_Position );
  end loop;

  for Front_Gear_Position in Front_Bottom_Gear .. Front_Top_Gear loop
    for Back_Gear_Position in Back_Bottom_Gear .. Back_Top_Gear loop

      Ada.Integer_Text_IO.Put
      (
        Item  => Front_Gear_Position,
        Width => 2
       );
      Ada.Text_IO.Put( " : " );
      Ada.Integer_Text_IO.Put
      (
        Item  => Front_Gear_Teeth( Front_Gear_Position ),
        Width => 3
      );
      Ada.Text_IO.Put( " , " );
      Ada.Integer_Text_IO.Put
      (
        Item  => Back_Gear_Position,
        Width => 2
      );
      Ada.Text_IO.Put( " : " );
      Ada.Integer_Text_IO.Put
      (
         Item  => Back_Gear_Teeth( Back_Gear_Position ),
         Width => 3
      );
      Ada.Text_IO.Put( " => " );
      Ada.Integer_Text_IO.Put
      (
        Item =>
          Front_Gear_Teeth( Front_Gear_Position ) *
          (
            Gear_Ratio_Base / Back_Gear_Teeth( Back_Gear_Position )
          ),
        Width => 8
      );
      Ada.Text_IO.Put( " :: " );
      Ada.Integer_Text_IO.Put
      (
        Item  => Gear_Ratio_Base,
        Width => 7
      );
      Ada.Text_IO.Put_Line( "" );

    end loop;
  end loop;

end Gears;