1. CSS342: Objects and Classes
Professor: Munehiro Fukuda
CSS342: Objects and Classes

2. CSS342: Objects and Classes
Today’s Topics
Class
Encapsulation and information hiding
From a abstract data specification to a class design
Examples
List: a list of students
Interface and implementation
Constructors and destructors
Rational: rational numbers
Operator overloading
CSS342: Objects and Classes

3. Encapsulation and Information Hiding
Class
Wall: Not only encapsulate the entire implementation but also make it invisible/inaccessible.
Slit : Interface of the implementation such as arguments and a return value.
Implementation
of method S
Program
that uses
method S
Function call with arguments
Return a value
CSS342: Objects and Classes

4. Class
Class
Classes: a new data type formed of a collection of data and a set of operations on the data
Data Structures: a construct within a programming language that stores a collection of data
Behave as a new data type
add
remove
query
Examples:
student lists
rational numbers
complex numbers
currency (cents/dollars)
length measurement (inches/feet)
weight measurement (oz/lbs)
Program
that uses
a class
CSS342: Objects and Classes

5. List Class Specification
Add a new student entry
Delete a student entry
Display a student entry
Check # students
Berger
Cioch
Olson
Erdly
Meske
Liu
McDaniel
Fukuda
Jackels
Smolar
Arnold
Frank
Clark
Bill
Dina
Baili
Janet
Munehiro
Chuck
Darian M F
0201
0202
0209
0203
0208
0206
0207
0204
0205
0210
Sorting depends on an implementation.
CSS342: Objects and Classes

6. CSS342: Objects and Classes
List Operations Spec.
Class
create( ):
creates an empty list.
destroy( ):
destroys a list.
insert( int index, Student item):
insert an item in front of the position index. Return true in success.
remove( int index ):
remove the item at the position index. Return true in success.
retrieve( int index, Student& item ):
retrieve the item at the position index, store it in item, and return true in success.
getLength( ):
return the number of items in a list.
isEmpty( ):
return true if the number of items is 0.
CSS342: Objects and Classes

7. create( )/constructor destroy( )/destructor
C++ Class
Class
public
member functions/methods
data members
Sorting depends on an implementation.
create( )/constructor
Berger
Cioch
Olson
Erdly
Meske
Liu
McDaniel
Fukuda
Jackels
Smolar
Arnold
Frank
Clark
Bill
Dina
Baili
Janet
Munehiro
Chuck
Darian M F
0201
0202
0209
0203
0208
0206
0207
0204
0205
0210
destroy( )/destructor
insert( )
remove( )
retrieve( )
getLength( )
isEmpty( )
Utility_func1( )
Utility_func2( )
private
CSS342: Objects and Classes

8. C++ Header and Implementation File
Class
Header File (.h)
Write a class specification
Summary of the class usage and behavior
Public member function prototypes
Private data members
Private member function prototypes
Implementation File (.cpp)
Code an implementation of each member function
ClassName::functionName
Function spec (pre/postconditions) in comments
The body of function with appropriate comments
CSS342: Objects and Classes

9. CSS342: Objects and Classes
List Header: list.h
Example: List
#ifndef _List_H_ // do not process below if this header has been already read by a compiler
#define _List_H_ // define “_List_H_” so that this header file will be never read again by a compiler
// Summary of the class usage and behavior
const int MAX_LIST = 100;
typedef Student ListItemType; // typedef int ListItemType in the following slides
class List {
Public:
List( ); // a constructor
// destructor is supplied by compiler
bool isEmpty( ) const; // returns true when a list has no items.
int getLength( ) const; // comments on each method
bool insert( int index, ListItemtype newItem );
bool remove( int index );
bool retrieve( int index, ListItemTpe& dataItem ) const;
priate:
vector<ListItemtype> items; // array implementation
int size; // # of items
int translate( int index ) const; // tranlate the index into the corresponding position }
#endif
CSS342: Objects and Classes

10. An Array Implementation of List Class list.cpp
Example: List
An Array Implementation of List Class list.cpp 12 3 19
100 ? 18 10 5 …. k
size
Positions in our list spec.
items
Array indexes
MAX_LIST – 1
MAX_LIST
k–1 1 2 4
CSS342: Objects and Classes

11. CSS342: Objects and Classes
Example: List
Constructor
A method that describes how an instance of the class is created:
Example 1:
List( ) {
items.resize( MAX_LIST ); }
List( int initSize ) {
if (initSize > 0 )
items.resize( initSize )
else
Example 2:
MyClass( int initialValue = 0 ) : myData( initialValue)
{ }
List list;
List list(10);
MyClass m;
MyClass m(10);
Initializer List
CSS342: Objects and Classes

12. CSS342: Objects and Classes
Why Initializer Lists?
Example: List
Are the following constructors correct?
Class List {
public:
List( string profName ) {
p.name = profName; }
private:
Professor p;
Class Professor {
Professor( string n ) {
name = n;
string name;
Class List {
public:
List( int courseNumber ) {
course = courseNumber; }
private:
const int course;
Class List {
public:
List( List &anotherSection ) {
another = anotherSection; }
private:
List &another;
CSS342: Objects and Classes

13. Insert insert( 3, newItem ) 44 Array indexes 1 2 3 k–1 k 12 3 19 100
Example: List
insert( 3, newItem ) 44
Shift 3
Shift 2
Shift 1
Array indexes 1 2 3
k–1
MAX_LIST – 1 k 12 3 19
100 …. 5 10 18 ? ? …. ?
size 1 2 3 4 k
MAX_LIST
Positions in our list spec.
bool List::insert( int index, ListItemType newItem ) {
if ( (index >= 1) && (index <= size + 1) && (size < MAX_LIST) ) {
for ( int pos = size; pos >= index; ––pos ) // shift from k to index to the right.
items[translate(pos+1)] = items[translate(pos)];
items[translate(index)] = newItem; // insert the item
++size; // increment # items
} else
return false; }
CSS342: Objects and Classes

14. Remove remove( 3 ) Array indexes 1 2 3 k–1 k 12 3 44 19 …. 5 10 18 ? ?
Example: List
remove( 3 )
Shift 1
Shift 2
Shift 3
Array indexes 1 2 3
k–1
MAX_LIST – 1 k 12 3 44 19 …. 5 10 18 ? ? …. ?
size 1 2 3 4 k
MAX_LIST
Positions in our list spec.
bool List::remove( int index ) {
if ( (index >= 1) && (index <= size) ) {
for ( int pos = index + 1; pos <= size; ++pos ) // shift from index+1 to k to the left.
items[translate(pos–1)] = items[translate(pos)];
––size; // decrement # items
return true;
} else
return false; }
CSS342: Objects and Classes

15. CSS342: Objects and Classes
Main program
Example: List
The main program to test your class is called: a driver program.
The driver program should test all your class methods.
Compilation: g++ list.cpp listDriver.cpp
#include “List.h”
int main( ) {
List aList;
ListItemType dataItem;
bool success;
success = aList.insert(1, 20);
aList.retrieve(1, dataItem); … }
CSS342: Objects and Classes

16. Class Rational Header File: rat.h from Deitel & Deitel
Example: Rational
Class Rational Header File: rat.h from Deitel & Deitel
#ifndef RAT_H // To prevent multiple definitions of the same header
#define RAT_H // If not fed into a compiler, mark this header as defined.
#include <iostream> // For outdate compilers, use #include <iostream.h>
using namespace std;
class Rational { // A class name should start from a capital letter.
public:
Rational ( int = 0, int = 1 ); // Default constructor.
Rational add( const Rational & a ); // Add a to this and return the result.
Rational subtract( const Rational & s ); // Subtract s from this and return the result.
Rational multiply( const Rational & m ); // Multiply this by m and return the result.
Rational divide( const Rational & d ); // Divide this by d and return the result.
void printRational( ) const; // Print numerator / denominator
private:
int numerator;
int denominator;
void reduce( ); // A utility function };
#endif
CSS342: Objects and Classes

17. Class Rational Implementation File: rat.cpp
Example: Rational
#include “rat.h” // You should insert blank lines for better readability.
Rational::Rational( int n, int d ) {
numerator = d < 0 ? –n : n; // sign+/- is added to the numerator
denominator = d < 0 ? –d; d;
reduce( ); // 3/6 → 1/2, 6/8 → 3/4 }
Rational Rational::add( const Rational& a ) { // n/d + N/D = (n * D + d * N) / (d * D)
Rational t;
t.numerator = numerator * a.denominator + denominator * a.numerator;
t.denominator = denominator * a.denominator;
t.reduce( );
return t;
Rational Rational::subtract( const Rational& s ) { // n/d – N/D = (n * D – d * N) / ( d * D)
t.numerator = numerator * s.denominator – denominator * s.numerator;
t.denominator = denominator * s.denominator;
CSS342: Objects and Classes

18. Class Rational Implementation File Cont'd
Example: Rational
Class Rational Implementation File Cont'd
Rational Rational::multiply( const Rational& m ) { // n/d * N/D = (n * N) / (d * D)
Rational t;
t.numerator = numerator * m.numerator;
t.denominator = denominator * m.denominator;
t.reduce( );
return t; }
Rational Rational::divide( const Rational& v ) { // n/d / N/D = n/d * D/N = (n * D) / (d * N)
t.numerator = numerator * v.denominator;
t.denominator = denominator * v.numerator;
void Rational::printRational( ) const {
if ( denominator == 0)
cout << “DIVIDE BY ZERO ERROR!!!” << endl;
else if (numerator == 0) // don’t print out … 0 / 5
cout << 0;
else
cout << numerator << “ / ” << denominator;
CSS342: Objects and Classes

19. Rational Class Implementation File Cont’d
Example: Rational
void Rational::reduce( ) {
int n = numerator < 0 ? –numerator : numerator; // get a positive numerator.
int d = denominator; // denominator is already positive.
int largest = n > d ? n : d; // max(n, d)
int gcd = 0; // great common divisor
for ( int loop = largest; loop >=2; loop-- ) // check if numerator and denominator
if ( numerator % loop == 0 && denominator % loop == 0 ) {// are divisible with loop [max(n,d)…2]
gcd = loop; // if so, that loop is gcd!
break; }
if (gcd != 0) { // If gcd has been found, divide them
numerator /= gcd; // by gcd.
denominator /= gcd;
CSS342: Objects and Classes

20. Class Rational Main Program: ratDriver.cpp
Example: Rational
Compilation: g++ rat.cpp ratDriver.cpp
#include <iostream.h>
#include “rat.h”
void main( ) {
Rational x(-2, 6), y(-14, -16), z;
x.printRational( ); cout << “ + ”; y.printRational( );
z = x.add(y);
cout << “ = ” << z.printRational( ) << endl;
// Repeat the same test for all methods. }
Question:
Why can’t we code like that?
z = x + y;
CSS342: Objects and Classes

21. Operator Overloading: rat2.cpp
Example: Rational
#ifndef RAT2_H
#define RAT2_H
#include <iostream> // for outdated compilers, #include <iostream.h>
using namespace std;
class Rational { // class spec including assumptions should be provided here
friend ostream& operator<< (ostream& output, constRational & r); // those two functions are stand-friend istream& operator>> ( istream& input, Rational & r ); // along functions.
public:
Rational( int = 0, int = 1 ); // constructor
Rational operator+(const Rational &) const; // arithmetic operators:this object + parameter
Rational operator–(const Rational &) const; // this object – parameter
Rational operator*(const Rational &) const; // this object * parameter
Rational operator/(const Rational &) const; // this object / parameter
bool operator>(const Rational &) const; // boolean comparison operators: this object > parameter ?
bool operator<(const Rational &) const; // this object < parameter ?
bool operator>=(const Rational &) const; // this object >= parameter ?
bool operator==(const Rational &) const; // this object == parameter ?
bool operator!=(const Rational &) const; // this object != parameter ?
Rational& operator+=(const Rational &); // assignment operators: this object += parameter
// You should also define operator–=, operator*=, and operator /=
private: // the same as rat.h };
#endif
CSS342: Objects and Classes

22. CSS342: Objects and Classes
+ Implementation
Example: Rational //
// overloaded +; this object + parameter
Rational Rational::operator+( const Rational& a ) const {
// operations are the same as Rational::add( const Rational& a )
Rational sum;
sum.numerator = numerator * a.denominator + denominator * a.numerator;
sum.denominator = denominator * a.denominator;
sum.reduce( );
return sum; }
CSS342: Objects and Classes

23. >, ==, and >= Implementation
Example: Rational
// >
// overloaded >; true if this object > parameter, otherwise false
bool Rational::operator>( const Rational& r ) const {
return float(numerator/denominator) > float(r.numerator/r.denominator);
// use float, otherwise fractions are truncated. }
// ==
// overloaded ==; true if this object == parameter, otherwise false
bool Rational::operator==( const Rational& r ) const {
return numerator == r.numerator && denominator == r.denominator; }
// >=
// overloaded >=; true if this object >= parameter, otherwise false
bool Rational::operator>=( const Rational& r ) const {
// once you have defined operators> and ==, you can use them.
return *this == r || *this > r; // this is a pointer to this object, and thus *this is this object itself. }
CSS342: Objects and Classes

24. CSS342: Objects and Classes
+= Implementation
Example: Rational
// =
// overloaded +=; this object += parameter
Rational& Rational::operator+=( const Rational& r ) {
// should not instantiate a new object. We’d rather add parameter to this object itself.
numerator = numerator * r.denominator + denominator * r.numerator;
denominator = denominator * r.denominator;
reduce( );
return *this; // why must we return the reference rather than the value? }
Example:
(a+=b)+=c
- if a value is returned:
1. a+=b computed; 2. A copy of a generated; 3. (this copy)+=c computed
- if the reference is returned:
1. a+=b computed; 2. The reference returned; 3. a+=c computed
CSS342: Objects and Classes

25. << Implementation
Example: Rational
// <<
// prints “DIVIDE BY ZERO ERROR!!!” if denominator is zero,
// prints whole numbers without denominator (as ints), otherwise uses ‘/’
ostream& operator<<( ostream& output, const Rational& r ) {
// we are operating on an ostream object, “output” rather than our Rational.
// ostream itself has an operator<< like operator<<(cont int&), operator<<(const float&).
// It is unfeasible to define ostream::operator<<(const Rational&)
// Thus, this operator<< must be defined as a stand-alone function
if (r.denominator == 0)
output << “DIVIDE BY ZERO ERROR!!!” << endl; // zero division
else if (r.numerator == 0)
output << 0; // zero rational
else if (r.denominatr == 1)
output << r.numerator; // whole number
else
output << r.numerator << “/” << r.denominator;
return output; }
CSS342: Objects and Classes

26. Class Rational Main Program: ratDriver.cpp
Example: Rational
#include <iostream.h>
#include “rat2.h”
void main( ) {
Rational x(-2, 6), y(-14, -16), z;
x.printRational( ); cout << “ + ”; y.printRational( );
z = x + y;
cout << “ = ” << z.printRational( ) << endl;
// Repeat the same test for all methods. }
CSS342: Objects and Classes