Object-oriented Software in Ada 95

Ada introduction: Part 1
4 Ada introduction: Part 2
This chapter looks at declarations and use of scalar data items in Ada. One of Ada's key contributions to
programming is the ability to declare data items that can only take a specific range of values. Ada’s strong
typing ensures that many errors in a program will be detected at compile rather than run-time.
4.1 Introduction
So far, only objects of type Integer or Character have been introduced. An Integer object stores a
number as a precise amount with no decimal places. The exact range of values that can be stored is
implementation defined. A user can find out this range by employing the attributes 'First and 'Last on the
type Integer. In addition the attribute 'Bits returns the size in bits of an Integer object. The following
program prints these attributes for an Integer type.
with Ada.Text_Io; use Ada.Text_Io;
procedure Main is
begin
Put("Smallest Integer ");Put( Integer'Image(Integer'First)); New_Line;
Put("Largest Integer ");Put( Integer'Image(Integer'Last)); New_Line;
Put("Integer (bits) ");Put( Integer'Image(Integer'Size )); New_Line;
end Main;
Note:
The attribute 'First is pronounced ‘tick first’.
When compiled and run on two different machines, this would produce:
Machine using a 16 bit word size
Smallest integer -32768
Largest integer 32767
Integer (bits) 16
Machine using a 32 bit word size
Smallest integer -2147483648
Largest integer 2147483647
Integer (bits) 32
4.2 The type Float
An instance of the type Integer holds numbers to an exact value. In the solution of some problems the numbers
manipulated will not be an exact value. For example, a person's weight is 80.23 kilograms. The data type Float
elaborates an object which can hold a number which has decimal places. Thus in a program a person's weight can
be held in the object weight which is declared as follows:
Weight : Float := 80.23;
A Float is implemented as a floating point number. A floating point number holds a value to a specific
number of decimal digits. This will in many cases be an approximation to the exact value which the programmer
wishes to store. For example, a 1/3 will be held as 0.333 ... 33. The following table shows how various numbers
are effectively stored in floating point form to 6 decimal places:
Number Scientific notation Floating point form
80.23 0.8023 * 102 +802300 +02
0.008023 0.8023 * 10-2 +802300 -02
0.333333 0.333333 * 100 +333333 +00
© M A Smith - May not be reproduced without permission