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Data Structures

CSCI 132, Spring 2014Lecture 2

Classes and Abstract Data TypesRead Ch 1.1 - 1.6

Read Style Guide (see course webpage)

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Abstraction and Data Hiding

Data Abstraction:

• Captures essential qualities of an object and names the object.

• Ignores implementation details

• Is necessary for managing large, complex software projects.

Data Hiding:

• Hides implementation details from user

• Prevents user from accessing implementation directly

• User must interact with object through an interface.

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Classes in C++

• A class is a means of abstraction in C++

• A class is a specification of a group of objects that all have the same essential properties

FOR EXAMPLE . . .

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A class example

classStudent

Properties (data members)

name, graduation year, list of courses,

number of courses

Operations (methods)List Courses

List Student Information

Add a Course

Set Graduation Date

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An object is an instance of a class

For example:

objectstudentA

Name: Andrea Student

Graduation Year: 2007

List of Courses: CSCI132, MATH331

Number of courses: 2

class Student Specification// SPECIFICATION FILE ( student.h )typedef char string9[10];class Student // declares a class data type{ // does not allocate memory

public : // 5 public function membersvoid AddCourse(string9 CourseName);void ListCourses(void) const;void ListInfo(void) const;void SetGradDate(int year);Student(); // Constructor FunctionStudent(char name[ ], int year);

private : // 4 private data memberschar studentName[30];string9 courses[6];int numCourses;int gradDate;

} ;

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Use of C++ data type class

• 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 objects or instances of the class.

• Client code uses public member functions to handle its class objects.

• Private members cannot be directly accessed by client code. It can only be accessed by member functions.

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#include "student.h" // includes specification of the class#include <iostream>using namespace std;int main ( void ){

int newYear;string9 newCourse;Student newStudent; // create new Student object

cout << "Enter graduation year: ";cin >> newYear;newStudent.SetGradDate(newYear); // set Graduation datecout << "Enter course to be added: ";cin >> newCourse;newStudent.AddCourse(newCourse); // Add a coursenewStudent.ListInfo(); // List Student informationnewStudent.ListCourses(); // List coursesreturn 0;

} // end of main

Client Code Using Student

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class type declaration

The class declaration creates a data type and names the members of the class.

It does not allocate memory for any variables of that type!

Client code still needs to declare class variables.

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C++ Data Type class represents an ADT

• 2 kinds of class members: data members and function members

• class members are private by default

• data members are generally private

• function members are generally declared public

• private class members can be accessed only by the class member functions, not by client code.

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2 separate files generally used for class type

// SPECIFICATION FILE ( student .h ) // Specifies the data and function members. class Student { public: . . .

private: . . . } ;

// IMPLEMENTATION FILE ( student.cc ) // Implements the Student member functions.

. . .

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Implementation file for Student

// IMPLEMENTATION FILE ( student.cc ) // Implements the Student member functions.

#include "student.h" // also must appear in client code #include <iostream> using namespace std;

. . .

void Student :: SetGradDate ( /* in */ int year ) { gradDate = year; }

. . .

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Class Constructors initialize Data Members

// In the file student.cc

Student :: Student () { //Default Constructor

numCourses = 0;

gradDate = 0;

strcpy(studentName, "John Doe");

}

// This is invoked in client code at time of object declaration:

// Student newStudent("Mary Contrary", 2010);

Student :: Student(char name[ ], int year) { //Constructor with parameters

//We will fill this out in lab!

}

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Function stubs

• Stubs allow you to test code that relies on unwritten functions. The stub often has no code in the function definition:

void Student :: AddCourse(string9 courseName) {

//empty

}

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Function drivers

Function drivers allow you to test class functions individually before writing the entire client code:

int main (void) {

Student newStudent;

newStudent.listInfo( );

}