Object-oriented Software in Ada 95

Arrays 105
with Ada.Text_Io, Class_Histogram;
use Ada.Text_Io, Class_Histogram;
procedure Main is
Ch:Character;
--Current character
Text_Histogram: Histogram; --Histogram object
begin
Reset(Text_Histogram); --Reset to empty
while not End_Of_File loop --For each line
while not End_Of_Line loop --For each character
Get(Ch);
--Get current character
Add_To( Text_Histogram, Ch ); --Add to histogram
end loop;
Skip_Line;
--Next line
end loop;
Put( Text_Histogram ); --Print histogram
end Main;
The class histogram is defined by the following package specification:
package Class_Histogram is
type Histogram is private;
Def_Height : constant Positive := 14;
procedure Reset( The:in out Histogram );
procedure Add_To( The:in out Histogram; A_Ch:in Character );
procedure Put(The:in Histogram; Height:in Positive:=Def_Height);
private
type Alphabet_Index is new Character range 'A' .. 'Z';
type Alphabet_Array is array (Alphabet_Index) of Natural;
type Histogram is record
Number_Of : Alphabet_Array := ( others => 0 );
end record;
end Class_Histogram;
The histogram is calculated using the individual letter frequencies that are stored in an array of Naturals
indexed by the upper case letters 'A' .. 'Z'. The implementation is simplified by allowing each letter to index
directly the frequency count for the letter.
In the implementation of the class histogram shown below, the procedure reset is used to set the
individual frequency counts for each letter to 0.
with Ada.Text_Io, Ada.Float_Text_Io, Ada.Characters.Handling;
use Ada.Text_Io, Ada.Float_Text_Io, Ada.Characters.Handling;
package body Class_Histogram is
procedure Reset(The:in out Histogram) is
begin
The.Number_Of := ( others => 0 ); --Reset counts to 0
end Reset;
The procedure Add_To uses the functions Is_Lower, To_Upper and Is_Upper which are contained in
the package Ada.Characters.Handling. A full description of these functions can be found in Section C.7,
Appendix C.
© M A Smith - May not be reproduced without permission