Object-oriented Software in Ada 95

Note:
In reality the floating point number will be held in binary.
Ada introduction: Part 2 39
The main consequence of using a floating point number is that numbers are held to an approximation of their
true value. Calculations using floating point numbers will usually only give an approximation to the true answer.
However, in many cases this approximation will not cause any problems. An area where this approximation will
cause problems is when the value represents a monetary amount.
The attributes 'First, 'Last and 'Size may also be applied to objects of type Float. In addition the
attribute 'Digits returns the precision in decimal digits of a number stored in a Float object. For example, the
following program:
with Ada.Text_Io;
use Ada.Text_Io;
procedure Main is
begin
Put("Smallest Float ");
Put( Float'Image( Float'First ) ); New_Line;
Put("Largest Float ");
Put( Float'Image( Float'Last ) ); New_Line;
Put("Float (bits) ");
Put( Integer'Image( Float'Size ) ); New_Line;
Put("Float (digits) ");
Put( Integer'Image( Float'digits ) ); New_Line;
end Main;
Note: Float'Image delivers a string representing a floating point number in scientific notation.
when compiled and run on two different machines would produce:
Machine using a 32 bit word size
Smallest Float -3.40282E+038
Largest Float 3.40282E+038
Float (bits) 32
Float (digits) 6
Machine using a 64 bit word size
Smallest Float -1.79769313486232E+308
Largest Float 1.79769313486232E+308
Float (bits) 64
Float (digits) 15
4.2.1 Other Integer and Float data types
Some implementations of Ada may provide data types that offer a greater precision than the in-built types of
Integer and Float. If these are provided they will be called Long_Integer, Long_Float,
Long_Long_Integer etc.
4.3 New data types
Using an object of type Integer to hold numeric values may be a useful approach, but it does not lead to a
program that is machine independent. For example, during its execution a program could create values which
were not containable in a particular machine's Integer object. If this happened, then the program would fail
with a run-time error of ‘Constraint_Error’.
Ada provides an elegant solution to this problem. It allows a user to define a new data type, which has a
specific range of values. For example, the following declaration defines a new data type Distance which will
hold the distance between two places:
type Distance is range 0 .. 250_000;
Note:
If the compiler cannot provide an object which can hold such a range, a compile-time error message
will be generated.
© M A Smith - May not be reproduced without permission