1. EECE.3220 Data Structures Instructor: Dr. Michael Geiger Spring 2019
Lecture 10:
Abstract data types
Classes

2. Data Structures: Lecture 9
Lecture outline
Announcements/reminders
HW 1 due Wednesday, 2/20
Problem set dealing with algorithmic complexity
No late submissions allowed (if exam on 2/22)
Program 2 to be posted; due TBD
Exam 1: TBD
Please respond to poll if you haven’t already
Today’s lecture
ADT intro
Class intro
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Data Structures: Lecture 9

3. Abstract data types (ADTs)
Processing data requires
Collection of data items
Basic operations to be performed on those items
Combination of the two: abstract data type (ADT)
“Abstract” part: definition of type separated from implementation
Look at storage of data without worrying about implementation
Example: “store 10 values”
Could use many different implementations
Algorithms defined for basic operations
Effectiveness of algorithm usually linked to underlying data structures
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Data Structures: Lecture 9

4. C-style data structures
Can be more efficient than C++ implementation
Example: array vs. C++ vector
May simplify implementation but add overhead in form of operations that aren’t used
Key C-style structures
Arrays (1-D or greater)
Structures
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Data Structures: Lecture 9

5. Data Structures: Lecture 9
Time
ADT to represent time
Data to be stored: hours, minutes, AM/PM, military (24-hour equivalent of 12-hour time)
Operations: set time, display time, advance time, compare times
Will define ADT using C-style implementation
Will re-define later using OOP implementation
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Data Structures: Lecture 9

6. Time structure, prototypes
struct Time { unsigned hour, minute; char AMorPM; // 'A' or 'P' unsigned milTime; // military time equivalent }; void set(Time &t, unsigned hours, unsigned minutes, char AMPM); void display(const Time &t, ostream &out); void advance(Time &t, unsigned hours, unsigned minutes); bool lessThan(const Time &t1, const Time &t2);
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Data Structures: Lecture 9

7. Classes, Objects, Member Functions and Data Members
Classes: user-defined types
Classes represent real concepts (e.g., car)
Functions describe mechanisms that perform tasks
Hide complex tasks from the user
Ex: driver can use gas pedal to accelerate without knowing how acceleration is performed
Must define classes before using them
Ex: a car must be designed and built before it can be driven
Many objects can be created from the same class
Object: instance of a particular type
In C++, every data type comes from an object
Ex: many cars can be built from same specifications
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Data Structures: Lecture 10

8. Structs and Classes: Similarities
Essentially the same syntax
Both are used to model objects with multiple attributes (characteristics)
represented as data members
also called fields … or …
instance or attribute variables.
Thus, both are used to process non-homogeneous data sets.
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Data Structures: Lecture 10

9. Structs vs. Classes: Differences
No classes in C
Members public by default
Can be specified private
Classes
Both structs and classes in C++
Structs can have members declared private
Class members are private by default
Can be specified public
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Data Structures: Lecture 10

10. Advantages in C++: (structs and classes)
C++ structs and classes model objects which have:
Attributes represented as data members
Operations represented as functions (or methods)
Leads to object oriented programming
Objects are self contained
"I can do it myself" mentality
They do not pass a parameter to an external function
If data member is private, can only be modified by member function
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Data Structures: Lecture 10

11. Data Structures: Lecture 10
Class Declaration
Syntax class ClassName { public: Declarations of public members private: Declarations of private members };
Order of public/private doesn’t matter
Members private by default  if you list private members first, you don’t need private keyword
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Data Structures: Lecture 10

12. Data Structures: Lecture 10
Designing a Class
Public members of class accessible to everyone
Most function members are public
Private members of class accessible only in member functions
Data members almost always private
Some private function members (helper or utility functions)
Class definition in .h file (i.e., Time.h)
Data members
Member function prototypes
Friend function prototypes
Function definitions in .cpp file (i.e., Time.cpp)
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Data Structures: Lecture 10

13. Data Structures: Lecture 10
Class implementation
One key point: within .cpp file, don’t know what namespace functions belong to
Function names must include class name as well
Format:
<class_name>::<function_name>([param list])
{ <function body> }
Example:
void GradeBook::setCourseName(string name)
{ courseName = name; }
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Data Structures: Lecture 10

14. Data Structures: Lecture 10
Data members
Local variables
Variables declared in a function definition’s body
Cannot be used outside of that function body
Lost when function terminates
Attributes
Exist throughout the life of the object
Represented as data members
Each object maintains its own copy of data members
Functions that change data members are called mutator functions (or “set” functions)
Functions that return data members are called accessor functions (or “get” functions)
Good programming practice: keep data private
Use mutators / accessors to set / get data
Allows programmer to control data accesses
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Data Structures: Lecture 10

15. Example: data members (GradeBook.h)
// GradeBook class interface class GradeBook { public: // function that sets the course name void setCourseName( string name ); // function that gets the course name string getCourseName(); // function that displays a welcome message void displayMessage(); private: string courseName; // course name for this GradeBook };
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Data Structures: Lecture 10

16. Example: data members (GradeBook.cpp)
// GradeBook class implementation #include “GradeBook.h” // function that sets the course name void GradeBook::setCourseName( string name ) { courseName = name; } // function that gets the course name string GradeBook::getCourseName() { return courseName; // function that displays a welcome message void GradeBook::displayMessage() { cout << "Welcome to the grade book for\n" << courseName << "!" << endl;
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Data Structures: Lecture 10

17. Data Structures: Lecture 10
Example (cont.)
int main() {
string nameOfCourse; // string of characters to store the course name
GradeBook myGradeBook; // create a GradeBook object named myGradeBook
// display initial value of courseName
cout << "Initial course name is: " << myGradeBook.getCourseName()
<< endl;
// prompt for, input and set course name
cout << "\nPlease enter the course name:" << endl;
getline( cin, nameOfCourse ); // read a course name with blanks
// This version of getline works with string objects
myGradeBook.setCourseName( nameOfCourse );
cout << endl;
myGradeBook.displayMessage();
return 0; }
Initial course name is:
Please enter the course name: EECE.3220
Welcome to the grade book for
EECE.3220!
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Data Structures: Lecture 10

18. Data Structures: Lecture 9
Final notes
Next time
More class details
Reminders:
HW 1 due Wednesday, 2/20
Problem set dealing with algorithmic complexity
No late submissions allowed (if exam on 2/22)
Program 2 to be posted; due TBD
Exam 1: TBD
Please respond to poll if you haven’t already
6/1/2019
Data Structures: Lecture 9