Object-oriented Software in Ada 95

Procedures and functions 61
The function M_To_K_Fun is used in the following program that will print a conversion table for miles to
kilometres. In Ada, a function or procedure may be declared in the declaration section of a procedure or function.
By using this technique, the types for Miles and Kilometres can be made visible to both the function
M_To_K_Fun and the main body of code that implements the printing of the conversion table.
with Ada.Text_Io, Ada.Float_Text_Io;
use Ada.Text_Io, Ada.Float_Text_Io;
procedure Main is
type Miles is digits 8 range 0.0 .. 25_000.0;
type Kilometres is digits 8 range 0.0 .. 50_000.0;
function M_To_K_Fun(M:in Miles) return Kilometres is
Kilometres_Per_Mile : constant := 1.609_344;
begin
return Kilometres( M * Kilometres_Per_Mile );
end M_To_K_Fun;
No_Miles : Miles;
begin
Put("Miles Kilometres"); New_Line;
No_Miles := 0.0;
while No_Miles 2, Exp=>0 ); Put(" ");
Put( Float( M_To_K_Fun( No_Miles ) ), Aft=>2, Exp=>0 );
New_Line;
No_Miles := No_Miles + 1.0;
end loop;
end Main;
When compiled, and run the above program will print the following results:
Miles Kilometres
0.00 0.00
1.00 1.61
2.00 3.22
3.00 4.83
4.00 6.44
5.00 8.05
6.00 9.66
7.00 11.27
8.00 12.87
9.00 14.48
10.00 16.09
5.2.1 Local variables
When a variable is declared inside a function, its lifetime is that of the function. When the function is entered,
space for any local variables is created automatically on a run-time stack. On exit from the function, the space
created for the local variables is returned to the system.
5.2.2 Separate compilation of functions
It is possible to compile the above function separately. However, if this is done the same types for Miles and
Kilometres must be used in both the main program and the function. One way of ensuring this is to use a
package that acts as a container for the types. This package is then made visible to both program units. The
following program illustrates this idea.
Firstly, the package that contains the types Miles and Kilometres is constructed.
© M A Smith - May not be reproduced without permission