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Prof. amr Goneid, AUC 1
CSCE 110CSCE 110PROGRAMMINGPROGRAMMING FUNDAMENTALSFUNDAMENTALS
WITH WITH C++C++
Prof. Amr GoneidProf. Amr GoneidAUCAUC
Part 14. User Defined ClassesPart 14. User Defined Classes
Prof. amr Goneid, AUC 3
User Defined ClassesUser Defined Classes OOP & Classes Data Encapsulation, Classes and objects Class Definition: Private & Public Members Constructors & Destructors Data and Function Members Accessors & Mutators Polymorphism and Overloading Example: Rational Numbers Class Example: Simple String Class
Prof. amr Goneid, AUC 4
1. OOP and Classes1. OOP and Classes Object-Oriented Programming (OOP)
focuses on creating ADT’s called “Classes” that identify “objects” and how they work together.
A class contains “data members” + “function members” in one object.
A member function tells an object to “operate on itself” in some way.
Objects are “self-contained”, carrying their own operations.
Prof. amr Goneid, AUC 5
2. Data Encapsulation, Classes 2. Data Encapsulation, Classes and Objectsand Objects A Class of objects is a user-defined Abstract Data
Type (ADT) An object is an instance of the class Once a class is defined, an object can be declared to
be of that type. For example, we have encountered the string class before. Since it has been defined, we can declare:string message;So, now message is an object of that class
Classes can be used by more than one program.
Prof. amr Goneid, AUC 6
Sharing ClassesSharing Classes
Class Class Class Class Class
Program Program Program
Standard Classes User Classes
Prof. amr Goneid, AUC 7
Classes & EncapsulationClasses & Encapsulation C++ classes are similar to structs, with the main
difference being that classes can have member functions, or methods, as well as variables, or data members in their definitions.
Combining data and operations (methods) together in an object is called encapsulation.
An object of a class can operate on itself by the methods or member functions of that class. e.g., an object of class string can operate by:
.find .length .at .erase etc
Prof. amr Goneid, AUC 8
3. Class Definition: Private & 3. Class Definition: Private & Public MembersPublic Members Classes use the technique of information hiding to
avoid incorrect use of the class. This is done by creating two areas: a public area, and a private area
public:Member Functions
private:Data members
Outside World
Prof. amr Goneid, AUC 9
Private & Public MembersPrivate & Public Members
External world has no access to the private area.
Users are allowed to operate on the objects of the class only via public member functions.
All member functions of a class have automatic access to all of the data members of that class.
Once we make a member variable a private member variable, there is then no way to change its value except by using one of the member functions.
Prof. amr Goneid, AUC 10
Class DefinitionClass DefinitionA class definition contains only the prototype for its member functionsand the definitions of the data members.It is declared in a class header file (.h) The implementations for the member functions are given elsewhere, in a class implementation file (.cpp) not in the header file .These two files form the Class Library.
Prof. amr Goneid, AUC 11
class ClassName { public:
function prototypes of methods and data members that are public and can be used by statements outside the class definition. private:
prototypes of functions and type definitions and variable declarations of data members that are
private and can be used only by statements inside the class definition.
}; // a semicolon must appear here
General Format of a Class General Format of a Class Declaration (in Header File)Declaration (in Header File)
Prof. amr Goneid, AUC 12
The name of the header file is the class name followed by “.h “ , e.g. ClassName.h
The name of the implementation file matches that of the header file with an extension of “.cpp”, e.g. ClassName.cpp
Application programs using the class are called “client programs”.
These programs must include:#include “ClassName.h”#include “Classname.cpp”
Class Library FilesClass Library Files
Prof. amr Goneid, AUC 13
Two special functions in the public part with thesame name as the class: The constructor is used to create and initialize
objects declared to be of that class There could be more than one constructor to
allow for different ways of initializing objects. The destructor is used to remove the objects
(specially when the data is allocated dynamically). Only one destructor is allowed.
4. Constructors and Destructors4. Constructors and Destructors
Prof. amr Goneid, AUC 14
//File: Time.h Time Class Header File#ifndef TIME_H // used to avoid multiple definitions #define TIME_H // not part of the classclass Time{
public: Time(); // constructor, a must~Time(); // destructor// Function prototypesvoid setTime (int, int, int);void displayTime (); const
private: int hour, minute, second;
}; // a semicolon must appear here#endif // TIME_H#include “Time.cpp"
5. Data & Function Members: Example 5. Data & Function Members: Example Header FileHeader File
Function cannot changeprivate members
Prof. amr Goneid, AUC 15
Implementing Member FunctionsImplementing Member Functions
A member function is implemented in the implementation file (.cpp). The format is:
<type> <class name> :: <function name> (param list){..function body ..}
The Scope resolution operator::: prefix for each member function
Informs the compiler that the function is a member of the class
Prof. amr Goneid, AUC 16
Example Implementation FileExample Implementation File//File: Time.cpp Time Class Implementation File#include <iostream>using namespace std;
Time :: Time(){ hour = minute = second = 0; }Time::~Time() { } // do nothing
void Time :: setTime(int h, int m, int s) { hour = (h >= 0 && h < 24) ? h : 0; minute = (m >= 0 && m < 60) ? m : 0; second = (s >= 0 && s < 60) ? s : 0; }void Time :: displayTime() const{ cout << hour << “:“ << minute << “:“ << second << endl; }
Prof. amr Goneid, AUC 17
ObjectsObjects Object: a particular instance of the class. To declare an object in a client program:
The same way we declare a variable but with the type = class name, e.g.
Time t1;Time T[20];
This will also invoke the constructor. The Dot Operator allows an object to access its
public members, e.g.t1.displayTime();
Prof. amr Goneid, AUC 18
Example of Application (Client) FileExample of Application (Client) File
//File: TimeAppl.cpp Time Class Application File#include “Time.h“#include <iostream>using namespace std;int main(){
Time t1 , t2;cout << “Start Time is: “; t1.displayTime ( );t2.setTime (5, 10, 30);cout << “End Time is: “; t2.displayTime ( );return 0;
}
Prof. amr Goneid, AUC 19
RemarksRemarks Every class should have a default constructor
(without parameters). The default constructor may also be implemented
as:Time ::Time( ) : hour(0), minute(0), second(0){ }
When used in the application program as:Time t1;then t1.hour, t1.minute and t1.second will be set initially to zero
member initializers
Prof. amr Goneid, AUC 20
RemarksRemarks An explicit value constructor may also be added
and defined as:Time( int , int , int);
and is implemented as:Time :: Time( int h, int m, int s){ hour = h; minute = m; second = s; }
We can use it in the application to initialize an object:Time t1(7,45,0);
const functions cannot modify private data members
Prof. amr Goneid, AUC 21
6. Accessors and Mutators6. Accessors and Mutators It is possible to extract a private data member
using an accessor function. For example, to access “hour”:int getHour( ) const; // Prototype
int Time::getHour( ) const // function definition{ return hour; }
Time t1;int h = t1.getHour( ); // invoking the function
A mutator member function (like setTime( )) will be able to change the private data members.
Prof. amr Goneid, AUC 22
7. Polymorphism & Overloading7. Polymorphism & Overloading Defining several functions with the same name is
called function overloading
The presence of more than one constructor for the class is an example of function overloading.
Polymorphism is what allows functions with the same name to do different things based on its arguments
Prof. amr Goneid, AUC 23
8. Example: ADT 8. Example: ADT rationalrational
Abstraction:A rational number (fraction) is a rational representation of two integers (x,y).
Elements or Members:A numerator (x) and a denominator (y), both are integers. (y) cannot be zero
Relationship:The representation is equivalent to x / y
Prof. amr Goneid, AUC 24
ADT ADT rationalrational (continued) (continued)
Fundamental Operations: Read a fraction from keyboard Display a fraction on the screen Add Fractions f = f1 + f2 (e.g. ½ + ¼ = ¾) Subtract Fractions f = f1 – f2 (e.g. ½ - 1/3 = 1/6) Multiply Fractions f = f1 * f2 (e.g. ½ * ¾ = 3/8) Divide Fractions f = f1 / f2 (e.g. 1/5 / ¼ = 4/5) Reduce Fractions (e.g. 2/6 = 1/3)
Prof. amr Goneid, AUC 25
Implementing a Implementing a rationalrational Class ClassWe will have 3 files:
“rational.h” to contain the class definition.
“rational.cpp” to contain the implementation of the member functions.
“RationalTest.cpp” an application file to test the class.
Prof. amr Goneid, AUC 26
The Header File: rational.hThe Header File: rational.h// File: rational.h// Rational class definition
#ifndef RATIONAL_H // used to avoid multiple definitions #define RATIONAL_H // not part of the class
class rational{ public:
// Member functions// Constructorsrational(); // Default Constructorrational(int); // Initialize numerator with denom = 1rational(int, int); // Initialize both numerator and denom.
Prof. amr Goneid, AUC 27
The Header File: rational.h (cont.)The Header File: rational.h (cont.)void setNum(int); // Set numerator and denominatorvoid setDenom(int);rational multiply(const rational &f); // Multiply fractionsrational divide(const rational &f);// Divide fractionsrational add(const rational &f); // Add Fractionsrational subtract(const rational &f); // Subtract Fractionsvoid readRational(); // Read a fractionvoid displayRational() const; // Display a fractionrational reduce() const; // Reduce fraction
// Accessorsint getNum() const;int getDenom() const;
Prof. amr Goneid, AUC 28
The Header File: rational.h (cont.)The Header File: rational.h (cont.)// Operator Style// Add object to parameterrational operator + (const rational &);// Test equality of object and parameter bool operator == (const rational &);
private:// Data members (attributes)int num; // private data fieldint denom; // private data field
}; // Note -- a class definition MUST end with a semicolon
#endif // RATIONAL_H#include "rational.cpp"
Prof. amr Goneid, AUC 29
The Implementation File: rational.cppThe Implementation File: rational.cpp// File: Rational.cpp// Rational class implementation
#include <iostream>using namespace std;
// Member functions// Constructorsrational::rational() // Default Costructor{ num = 0; denom = 0; }
rational::rational(int n) // Class Constructor{ num = n; denom = 1; }
rational::rational(int n, int d) // Class Constructor{ num = n; denom = d; }
Prof. amr Goneid, AUC 30
The Implementation File: rational.cppThe Implementation File: rational.cpp// Set numerator and denominatorvoid rational::setNum(int n){ num = n; }void rational::setDenom(int d){ denom = d; }
// Multiply fractionsrational rational::multiply(const rational &f){ rational temp(num * f.num, denom * f.denom); return temp; }
// Divide fractionsrational rational::divide(const rational &f){ rational temp(num * f.denom, denom * f.num); return temp; }
Prof. amr Goneid, AUC 31
The Implementation File: rational.cppThe Implementation File: rational.cpp// Add fractionsrational rational::add(const rational &f){ rational temp(num * f.denom + f.num * denom, denom * f.denom); return temp;}
// Subtract Fractionsrational rational::subtract(const rational &f) { rational temp(num * f.denom - f.num * denom, denom * f.denom); return temp;}
Prof. amr Goneid, AUC 32
The Implementation File: rational.cppThe Implementation File: rational.cpp// Read a fractionvoid rational::readRational(){ char slash; // storage for / do { cout << "Enter numerator / denominator: "; cin >> num >> slash >> denom; } while (slash != '/');}
// Display a fractionvoid rational::displayRational() const{ cout << num << '/' << denom;}
Prof. amr Goneid, AUC 33
The Implementation File: rational.cppThe Implementation File: rational.cpp// Reduce rationalrational rational::reduce() const{ int n,m,rem,gcd;
// Get the two integersn = abs(num); m = abs(denom);while (n > 0){
rem = m % n;m = n;n = rem;
}gcd = m;rational g (num/gcd, denom/gcd);return g;
}
Prof. amr Goneid, AUC 34
The Implementation File: rational.cppThe Implementation File: rational.cpp// Accessorsint rational::getNum() const{ return num; }int rational::getDenom() const{ return denom; }
// Operator-Likerational rational::operator + (const rational &f2){ rational temp (num * f2.denom + f2.num * denom, denom *
f2.denom); return temp; }
bool rational::operator == (const rational &f){ return (num == f.num && denom == f.denom); }
Prof. amr Goneid, AUC 35
RemarksRemarks It is possible to create a temporary class object within
a member function and initialize it using a constructor, e.g.rational rational::multiply(const rational &f){ rational temp (num * f.num, denom * f.denom);
return temp; }
A regular C++ operator can be “overloaded” to perform a different action on class objects. A member function can be defined to do this. If is an operator, the prototype will be:
<type> operator (parameter);e.g.
bool operator == (const rational &);
Prof. amr Goneid, AUC 36
RemarksRemarks The definition will be:
<type> <ClassName>::operator (parameter);e.g.bool rational::operator == (const rational &f){ return (num == f.num && denom == f.denom); }
For example:rational a , b;An expression of the form (a == b) will be evaluated as:
(a.num == b.num) && (a.denom == b.denom)
Prof. amr Goneid, AUC 37
The Application File: RationalTest.cppThe Application File: RationalTest.cpp// File: RationalTest.cpp// Tests the rational class#include <iostream>#include "rational.h“using namespace std;
int main(){
rational f1, f2;rational f3;// Read two rational numberscout << "Enter 1st fraction:" << endl;f1.readRational();cout << "Enter 2nd fraction:" << endl;f2.readRational();
Prof. amr Goneid, AUC 38
The Application File: RationalTest.cppThe Application File: RationalTest.cpp// Fraction Arithmeticf3 = f1.multiply(f2);f1.displayRational(); cout << " * ";f2.displayRational(); cout << " = ";f3.displayRational(); cout << " = "; f3 = f3.reduce();f3.displayRational(); cout << endl;
f3 = f1.divide(f2);f1.displayRational(); cout << " / ";f2.displayRational(); cout << " = ";f3.displayRational(); cout << " = "; f3 = f3.reduce();f3.displayRational(); cout << endl;
Prof. amr Goneid, AUC 39
The Application File: RationalTest.cppThe Application File: RationalTest.cppf3 = f1.add(f2);f1.displayRational(); cout << " + ";f2.displayRational(); cout << " = ";f3.displayRational(); cout << " = "; f3 = f3.reduce();f3.displayRational(); cout << endl;
f3 = f1 + f2; // uses operator “+” for additionf1.displayRational(); cout << " + ";f2.displayRational(); cout << " = ";f3.displayRational(); cout << " = "; f3 = f3.reduce();f3.displayRational(); cout << endl;
Prof. amr Goneid, AUC 40
The Application File: RationalTest.cppThe Application File: RationalTest.cppf3 = f1.subtract(f2);f1.displayRational(); cout << " - ";f2.displayRational(); cout << " = ";f3.displayRational(); cout << " = ";f3 = f3.reduce();f3.displayRational(); cout << endl;
return 0;
}
Prof. amr Goneid, AUC 41
Sample Run of RationalTest.cppSample Run of RationalTest.cppEnter 1st fraction:Enter numerator / denominator: 2/6Enter 2nd fraction:Enter numerator / denominator: 3/82/6 * 3/8 = 6/48 = 1/82/6 / 3/8 = 16/18 = 8/92/6 + 3/8 = 34/48 = 17/242/6 + 3/8 = 34/48 = 17/242/6 - 3/8 = -2/48 = -1/24Press any key to continue
Prof. amr Goneid, AUC 42
9. Example: Simple String Class9. Example: Simple String ClassHere we build a simple string class to do few tasks on our own string objects, e.g.read, write, get the character at a given location, etc.We implement the string as a dynamic array of characters. We will have 3 files:
“simpleString.h” to contain the class definition. “simpleString.cpp” to contain the implementation of
the member functions. “simpleStringTest.cpp” an application file to test
the class.
Prof. amr Goneid, AUC 43
The Header File: simpleString.hThe Header File: simpleString.h// File simpleString.h// Simple string class definition#ifndef SIMPLESTRING_H#define SIMPLESTRING_Hclass simpleString{ public:// Member Functions// Constructors
simpleString();simpleString(int );
// Destructor ~simpleString();
Prof. amr Goneid, AUC 44
The Header File: simpleString.hThe Header File: simpleString.h// Function Prototype definition// Read a simple string void readString();// Display a simple string void writeString() const;// Retrieve the character at a specified position// Returns the character \0 if position is out of bounds char at(int) const;// Return the string length int getLength() const;// Return the string capacity int getCapacity() const;// Get the contents into an array void getContents(char[ ]) const;
Prof. amr Goneid, AUC 45
The Header File: simpleString.hThe Header File: simpleString.hprivate: // Data members (attributes)
// maximum size int capacity; // pointer to a dynamic storage array
char *s; // current length
int length; };#endif //SIMPLESTRING_H #include "simpleString.cpp"
Prof. amr Goneid, AUC 46
The Implementation File: simpleString.cppThe Implementation File: simpleString.cpp// File: simplestring.cpp// Simple string class implementation#include <iostream>using namespace std;// Member Functions...// default constructor, capacity = 255simpleString::simpleString(){ s = new char[255]; capacity = 255; length = 0; }// Constructor with argument, capacity is mValsimpleString::simpleString(int mVal){ s = new char [mVal]; capacity = mVal; length = 0;}
// Class DestructorsimpleString::~simpleString(){ delete [ ] s;}
Prof. amr Goneid, AUC 47
The Implementation File: simpleString.cppThe Implementation File: simpleString.cpp// Read a simple stringvoid simpleString::readString(){ char next; int pos = 0;
cin.get(next); while ((next != '\n') && (pos < capacity)) { // Insert next in array contents s[pos] = next; pos++; cin.get(next); } length = pos; }
Prof. amr Goneid, AUC 48
The Implementation File: simpleString.cppThe Implementation File: simpleString.cpp// Write a simple stringvoid simpleString::writeString() const{ for (int pos = 0; pos < length; pos++) cout << s[pos]; }
// Character at (pos). Returns \0 if position is out of boundschar simpleString::at(int pos) const {
const char nullcharacter = '\0'; if ((pos < 0) || (pos >= length))
{cerr << "position " <<pos << " not defined." << endl;return nullcharacter;
} else return s[pos];}
Prof. amr Goneid, AUC 49
The Implementation File: simpleString.cppThe Implementation File: simpleString.cpp// Return the string lengthint simpleString::getLength() const{ return length; }
// Return the string capacityint simpleString::getCapacity() const{ return capacity; }// Get the contents into an arrayvoid simpleString::getContents(char str[ ]) const{ for (int i = 0; i < length; i++) str[i] = s[i];}
Prof. amr Goneid, AUC 50
The Application File: simpleStringTest.cppThe Application File: simpleStringTest.cpp// File: simpleStringTest.cpp// Tests the simple string class
#include "simpleString.h“#include <iostream>using namespace std;
int main(){
simpleString S1;simpleString S2(20);
cout << S1.getCapacity() <<" "<<S1.getLength() << endl;cout << S2.getCapacity() <<" "<<S2.getLength() << endl;
Prof. amr Goneid, AUC 51
The Application File: simpleStringTest.cppThe Application File: simpleStringTest.cpp // Read in a string.
cout << "Enter a string and press RETURN: ";S1.readString();
// Display the string just read. cout << "The string read was: "; S1.writeString(); cout << endl; // Display each character on a separate line. cout << "The characters in the string follow:" << endl; for (int pos = 0; pos < S1.getLength(); pos++) cout << S1.at(pos) << endl;
return 0;}