Thursday 2/7 Week 4

Thursday 2/7 Week 4

Chapter 4

Student Notes

Objectives

Enumeration Types

Intro to packages

1. Enumeration types

· Definition:

· Useful for representing a fixed set of values that are

· TYPE Expenses IS (entertainment, rent, utilities, food, clothing, automobile, insurance, miscellaneous);

ExpenseKind : Expenses;

· Entertainment etc called

· It is legal for the same enumeration literal to appear in more than one enumeration type. Ex

TYPE Traffic_Colors IS (Red, Yellow, Green);

TYPE Primary_Colors IS (Red, Yellow, Blue);

TYPE TV_Colors IS (Red, Blue, Green);

2. Enumeration type Attributes and Operations

· Consider the following Enumeration type:

TYPE Days IS (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday);

Today : Days; -- current day of the week

Tomorrow : Days; -- day after Today

· Enumeration types are useful because

· Each literal has a position in the list, starting with

· First, gives the first, or lowest, value in the list

· Last, gives the last or greatest value in the list

· Pos, given the of an enumeration type, return the of that value in the list

· Val, given the of an enumeration type, returns the of the enumeration type at that position

· Pred, given a of an enumeration type, returns the of that value

· Succ, given a of an enumeration type, returns the of that value

Given that Today := Friday; and Tomorrow := Saturday;

Days’First is

Days’Last is

Days’Pos(Tuesday) is

Days’Val(1) is

Days’Pos(Sunday) is

Days’Val(6) is

Days’Pred(Tomorrow) is

Days’Pred(Today) is

Days’Succ(Monday) is

Days’Succ(Today) is

· Note that enumeration types are not cyclical, they do not “wrap around” and therefore some queries will generate a Constraint_Error

· Days’Pred(Monday); or Days’Succ(Sunday); or possibly

Tomorrow := Days’Succ(Today);

3. Input/Output with Enumeration Types

· Enumeration types need I/O, but cannot use Ada.Text_IO because enumeration types are each a unique type

· There is a in Ada which allows for enumeration I/O.

· In order to use this for our type, an of the generic package must be created. This is called the package.

PACKAGE Day_IO IS NEW Ada.Text_IO.Enumeration_IO(Enum => Days);

· This gives us the ability to use Get and Put operations

· Day_IO.Get(Item => Today);

· Day_IO.Put(Item => Today);

· Day_IO.Put(Item => Today, Width => 10);

· Day_IO.Put(Item => Today, Width => 10, Set => Text_IO.Lower_Case);

· Day_IO.Put(Item => Today, Width => 10, Set => Text_IO.Upper_Case);

· When using Get, you will raise a Data_Error is you try to get a value that is not of the enumeration type

· Ex. colors.adb

4. Intro to packages

· We will be looking at a package specification for the Ada.Calendar package

· The specification serves two roles:

· AND

· Some resources available in a package are type and subtypes, procedures, and functions

· Ex. Ada.Calendar

· PRIVATE types specify a type whose details