Object-oriented Software in Ada 95

58 Ada introduction: Part 2
K : constant := 1024;
type Word16 is mod 64 * K;
Pattern : Word16;
the following code:
• sets the top nibble of the two byte word Pattern to zero.
Pattern := Pattern and 16#FFF#;
• sets bit 9 in the two byte word Pattern to 1.
Pattern := Pattern or 2#0000001000000000#;
Note:
The constant to base 16 is 16#FFF# and to base 2 is 2#0000001000000000#. Section B.4,
Appendix B describes how to declare constants to different bases.
• Flips bit 9 in the two byte word Pattern. If bit 9 were a 1 it would now be a 0 and if it were a 0 it
would now be a 1.
Pattern := Pattern xor 2#0000001000000000#;
• Inverts the bits in the two byte word Pattern.
4.20 Self-assessment
Pattern := not Pattern;
• Why is it not always appropriate to hold a value using an instance of a Float?
• How in a program can you find out the smallest value that can be stored in an instance of
Long_Integer?
• What are the benefits of user defined types and subtypes in a program?
• Why does the following program fail?
procedure Main is
type Miles is new Integer range 0 .. 100;
type Kilometres is new Integer range 0 .. 100;
London_Brighton : Miles := 50;
To_Brighton : constant Kilometres := 2;
Distance_To_London : Miles;
begin
Distance_To_London := London_Brighton + To_Brighton;
End Main;
• What is the difference between a type and a subtype?
• Why are the concepts of universal integer and universal float important?
• How can you convert a value of one type to that of another?
• Using the type declarations:
© M A Smith - May not be reproduced without permission