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Chapter 11- 2

Structured Types,Data

Abstraction

and Classes

Dale/Weems

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Hierarchical Structures The type of a struct member can be

another struct type

This is called nested or hierarchical structures

Hierarchical structures are very useful when there is much detailed information in each record

For example . . .

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struct MachineRecInformation about each machine in a shop contains:

an idNumber,

a written description,

the purchase date,

the cost,

and a history (including failure rate, number of

days down, and date of last service)

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struct DateType{ int month; // Assume 1 . . 12 int day; // Assume 1 . . 31 int year; // Assume 1900 . . 2050};struct StatisticsType{ float failRate;

DateType lastServiced; // DateType is a struct type int downDays;

};struct MachineRec{ int idNumber;

string description; StatisticsType history; // StatisticsType is a struct DateType purchaseDate;

float cost;};MachineRec machine;

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struct type variable machine

7000

.idNumber .description . history .purchaseDate .cost

.month .day .year

5719 “DRILLING…” 3 21 1995 8000.0

.failrate .lastServiced .downdays

.02 1 25 1999 4.month .day.year

machine.history.lastServiced.year has value 1999

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Unions in C++

DEFINITION

A union is a struct that holds only one of its members at a time during program execution.

EXAMPLE

union WeightType

{

long wtInOunces; int wtInPounds; Only one at a time

float wtInTons;

};

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Using Unions

union WeightType // Declares a union type{ long wtInOunces; int wtInPounds; float wtInTons; };

WeightType weight; // Declares a union variable

weight.wtInTons = 4.83;

// Weight in tons is no longer needed// Reuse the memory space

weight.wtInPounds = 35;7

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Abstraction

Abstraction is the separation of the essential qualities of an object from the details of how it works or is composed

Focuses on what, not how

Is necessary for managing large, complex software projects

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Control Abstraction

Constrol abstraction separates the logical properties of an action from its implementation

Search (list, item, length, where, found);

The function call depends on the function’s specification (description), not its implementation (algorithm)

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Data Abstraction

Data abstraction separates the logical properties of a data type from its implementation

LOGICAL PROPERTIES IMPLEMENTATION

What are the possible values? How can this be done in C++?

What operations will be needed? How can data types be used?

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Data Type

set of values(domain)

allowable operationson those values

FOR EXAMPLE, data type int has

domain

-32768 . . . 32767

operations

+, -, *, /, %, >>, <<

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Abstract Data Type (ADT)

An abstract data type is a data type whose properties (domain and operations) are specified (what) independently of any particular implementation (how)

For example . . .

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ADT Specification Example

TYPETime

DOMAINEach Time value is a time in hours, minutes, and seconds.

OPERATIONSSet the timePrint the timeIncrement by one secondCompare 2 times for equalityDetermine if one time is “less than” another

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Another ADT Specification

TYPEComplexNumber

DOMAIN

Each value is an ordered pair of real numbers (a, b) representing a + bi

OPERATIONSInitialize the complex numberWrite the complex numberAdd SubtractMultiplyDivideDetermine the absolute value of a complex number

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ADT Implementation

ADT implementation Choose a specific data representation

for the abstract data using data types that already exist (built-in or programmer-defined)

Write functions for each allowable operation

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10 45 27

Several Possible Representations of ADT Time

3 int variables

3 strings

3-element int array

Choice of representation depends on time, space, and algorithms needed to implement operations

10 45 27

“10” “45” “27”

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Some Possible Representationsof ADT ComplexNumberstruct with 2 float members

2-element float array

-16.2 5.8

-16.2 5.8

.real .imag

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C++ Data TypesC++ Data Types

structured

array struct union class

address

pointer reference

simple

integral enum

char short int long bool

floating

float double long double

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class Time Specification// Specification file (Time.h)

class Time // Declares a class data type{ // does not allocate memory

public : // Five public function members

void Set (int hours , int mins , int secs); void Increment (); void Write () const; bool Equal (Time otherTime) const; bool LessThan (Time otherTime) const;

private : // Three private data members

int hrs; int mins; int secs;

};

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C++ classType

Facilitates re-use of C++ code for an ADT

Software that uses the class is called a client

Variables of the class type are called class objects or class instances

Client code uses class’s public member functions to manipulate class objects

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Client Code Using Time#include “time.h” // Includes specification of the classusing namespace std;

int main (){ Time currentTime; // Declares two objects of Time Time endTime; bool done = false;

currentTime.Set (5, 30, 0); endTime.Set (18, 30, 0); while (! done) { . . .

currentTime.Increment (); if (currentTime.Equal (endTime))

done = true; };}

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The End of Chapter 11 – Part 2