Object-oriented Software in Ada 95

172 Child libraries
12.2 A rational arithmetic package
If precise arithmetic with rational numbers is required the Ada language can be extended by the inclusion of a
package that provides a new type Rational. Instances of this type may be used as if they were normal numeric
values such as integer.
The following extension to the language Ada is created by defining the class Rational. This class defines
the following operations: +, -, * on an instance of a Rational number.
The responsibilities of this class are as follows::
Method Responsibility
+ Delivers the sum of two rational numbers as a rational number.
- Delivers the difference of two rational numbers as a rational
number.
* Delivers the product of two rational numbers as a rational
number.
/ Delivers the division of two rational numbers as a rational
number.
In addition the following methods are used to create a rational constant and to help output a rational number in
a canonical form.
Method
Rat_Const
Image
Responsibility
Creates a rational number from two Integer numbers.
Returns a string image of a rational number in the canonical
form ‘a b/c’. For example:
Put( Image( Rat_Const(3,2) ) );
would print
1 1/2
12.2.1 Ada specification of the package
The specification of the package is as follows:
package Class_Rational is
type Rational is private;
function "+" ( F:in Rational; S:in Rational ) return Rational;
function "-" ( F:in Rational; S:in Rational ) return Rational;
function "*" ( F:in Rational; S:in Rational ) return Rational;
function "/" ( F:in Rational; S:in Rational ) return Rational;
function Rat_Const( F:in Integer;
S:in Integer:=1 ) return Rational;
function Image( The:in Rational ) return String;
private
type Rational is record
Above : Integer := 0; --Numerator
Below : Integer := 1;
end record;
end Class_Rational;
--Denominator
© M A Smith - May not be reproduced without permission