CSCE 210 Data Structures and Algorithms Prof. Amr Goneid AUC Part R1. ADTs as Classes Prof. Amr Goneid, AUC

ADTs as Classes Class Definition: Private & Public Members Constructors & Destructor Data and Function Members Accessors & Mutators Polymorphism and Overloading Example: Rational Numbers Class Example: Simple String Class Prof. Amr Goneid, AUC

1. Class Definition: Private & Public 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 Outside World private: Data members Prof. Amr Goneid, AUC

Private & 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

Class Definition A class definition contains only the prototype for its member functions and 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

General Format of a Class Declaration (in Header File) 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 Prof. Amr Goneid, AUC

Class Library Files 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” Prof. Amr Goneid, AUC

2. Constructors and Destructors Two special functions in the public part with the same 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. Prof. Amr Goneid, AUC

3. Data & Function Members: Example Header File //File: Time.h Time Class Header File #ifndef TIME_H // used to avoid multiple definitions #define TIME_H // not part of the class class Time { public: Time(); // constructor, a must ~Time(); // destructor // Function prototypes void setTime (int, int, int); void displayTime (); const private: int hour, minute, second; }; // a semicolon must appear here #endif // TIME_H #include “Time.cpp" Function cannot change private members Prof. Amr Goneid, AUC

Implementing 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

Example 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

Objects 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

Example 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

Remarks 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

Remarks 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

4. 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

5. 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

6. Example: ADT rational 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

ADT rational (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

Implementing a rational Class We 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

The Header 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 // Constructors rational(); // Default Costructor rational(int); // Initialize numerator with denom = 1 rational(int, int); // Initialize both numerator and denom. Prof. Amr Goneid, AUC

The Header File: rational.h (cont.) void setNum(int); // Set numerator and denominator void setDenom(int); rational multiply(const rational &f); // Multiply fractions rational divide(const rational &f); // Divide fractions rational add(const rational &f); // Add Fractions rational subtract(const rational &f); // Subtract Fractions void readRational(); // Read a fraction void displayRational() const; // Display a fraction rational reduce() const; // Reduce fraction // Accessors int getNum() const; int getDenom() const; Prof. Amr Goneid, AUC

The Header File: rational.h (cont.) // Operator Style // Add object to parameter rational operator + (const rational &); // Test equality of object and parameter bool operator == (const rational &); private: // Data members (attributes) int num; // private data field int denom; // private data field }; // Note -- a class definition MUST end with a semicolon #endif // RATIONAL_H #include "rational.cpp" Prof. Amr Goneid, AUC

The Implementation File: rational.cpp // Rational class implementation #include <iostream> using namespace std; // Member functions // Constructors rational::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

The Implementation File: rational.cpp // Set numerator and denominator void rational::setNum(int n) { num = n; } void rational::setDenom(int d) { denom = d; } // Multiply fractions rational rational::multiply(const rational &f) { rational temp(num * f.num, denom * f.denom); return temp; } // Divide fractions rational rational::divide(const rational &f) { rational temp(num * f.denom, denom * f.num); Prof. Amr Goneid, AUC

The Implementation File: rational.cpp // Add fractions rational rational::add(const rational &f) { rational temp(num * f.denom + f.num * denom, denom * f.denom); return temp; } // Subtract Fractions rational rational::subtract(const rational &f) rational temp(num * f.denom - f.num * denom, Prof. Amr Goneid, AUC

The Implementation File: rational.cpp // Read a fraction void rational::readRational() { char slash; // storage for / do cout << "Enter numerator / denominator: "; cin >> num >> slash >> denom; } while (slash != '/'); // Display a fraction void rational::displayRational() const cout << num << '/' << denom; Prof. Amr Goneid, AUC

The Implementation File: rational.cpp // Reduce rational rational rational::reduce() const { int n,m,rem,gcd; // Get the two integers n = 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

The Implementation File: rational.cpp // Accessors int rational::getNum() const { return num; } int rational::getDenom() const { return denom; } // Operator-Like rational 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

Remarks 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

Remarks 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

The Application 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 numbers cout << "Enter 1st fraction:" << endl; f1.readRational(); cout << "Enter 2nd fraction:" << endl; f2.readRational(); Prof. Amr Goneid, AUC

The Application File: RationalTest.cpp // Fraction Arithmetic f3 = 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 << " / "; cout << " = "; f3 = f3.reduce(); f3.displayRational(); cout << endl; Prof. Amr Goneid, AUC

The Application File: RationalTest.cpp f3 = 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 addition Prof. Amr Goneid, AUC

The Application File: RationalTest.cpp f3 = 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

Sample Run of RationalTest.cpp Enter 1st fraction: Enter numerator / denominator: 2/6 Enter 2nd fraction: Enter numerator / denominator: 3/8 2/6 * 3/8 = 6/48 = 1/8 2/6 / 3/8 = 16/18 = 8/9 2/6 + 3/8 = 34/48 = 17/24 2/6 - 3/8 = -2/48 = -1/24 Press any key to continue Prof. Amr Goneid, AUC

7. Example: Simple String Class Here 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

The Header File: simpleString.h // Simple string class definition #ifndef SIMPLESTRING_H #define SIMPLESTRING_H class simpleString { public: // Member Functions // Constructors simpleString(); simpleString(int ); // Destructor ~simpleString(); Prof. Amr Goneid, AUC

The 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

The Header File: simpleString.h private: // 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

The Implementation File: simpleString.cpp // Simple string class implementation #include <iostream> using namespace std; // Member Functions... // default constructor, capacity = 255 simpleString::simpleString() { s = new char[255]; capacity = 255; length = 0; } // Constructor with argument, capacity is mVal simpleString::simpleString(int mVal) { s = new char [mVal]; capacity = mVal; length = 0;} // Class Destructor simpleString::~simpleString() { delete [ ] s;} Prof. Amr Goneid, AUC

The Implementation File: simpleString.cpp // Read a simple string void 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

The Implementation File: simpleString.cpp // Write a simple string void simpleString::writeString() const { for (int pos = 0; pos < length; pos++) cout << s[pos]; } // Character at (pos). Returns \0 if position is out of bounds char 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

The Implementation File: simpleString.cpp // Return the string length int simpleString::getLength() const { return length; } // Return the string capacity int simpleString::getCapacity() const { return capacity; } // Get the contents into an array void simpleString::getContents(char str[ ]) const { for (int i = 0; i < length; i++) str[i] = s[i]; } Prof. Amr Goneid, AUC

The Application 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

The 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; } Prof. Amr Goneid, AUC

Sample Run of simpleStringTest.cpp 255 0 20 0 Enter a string and press RETURN: User Classes The string read was: User Classes The characters in the string follow: U s e r C l a Press any key to continue Prof. Amr Goneid, AUC

Learn on your own about: Procedural vs. OOP Translating a Library Inline Functions Overloading insertion and extraction operators Conditional Compilation Standard I/O Classes The C++ String Class Prof. Amr Goneid, AUC