CMSC 202 Lesson 7 Classes I

Warmup Add the correct parameter list and return type to the following function: (hint: all the information you need is in the function) _____ findDVD( _________ Titles, _________ titleToFind) { for (unsigned int i = 0; i < Titles.size(); ++i) if (Titles.at(i) == titleToFind) return i; } return Titles.size();

Object-Oriented Programming (OOP) Software Development Goals Code Reuse – save money and time Abstraction – reduce something to essentials Examples: Driving a car Controlling a television OOP Key Components (Classes) Data Operations (methods/functions) Usually associated with the data Encapsulation Details of implementation (both data and algorithms) is hidden from the user of a class

OOP Example Driving a car… Car Data Car Operations Encapsulation? Amount of Gas Current Gear Automatic or Manual Mileage Current Amount of Turn Car Operations Accelerate Brake Change Gear Add Gas Turn right Turn left Encapsulation?

OOP Example What properties (data) does a chair have? What actions (operations) does a chair have?

Practice Box of DVDs What data does the box have? What operations does the box have?

Structures What about structs? struct DayOfYear { int month; int day; Collection of data No operations explicitly related struct DayOfYear { int month; int day; }; DayOfYear july4th; july4th.month = 7; july4th.day = 4; No typedef! Members

Structures Good Bad Simple Can be parameters to functions Can be returned by functions Can be used as members of other structs Bad No operations Data is not protected Any code that has access to the struct object has direct access to all members of that object

Classes Class Object Car My physical car Building ITE Building Chair Collection of data and Operations on that data Object Instance of a class Examples (on right!) Blueprint, pattern, classification Thing you built, made, constructed Class Object Car My physical car Building ITE Building Chair This particular chair Marker A particular marker Date July 4th, 05

Classes – a Struct Replacement Good Simple Objects can be parameters to functions Objects can be returned by functions Objects can be members of other classes Operations linked to data Data is protected Code that uses an object MUST use the operators of the class to access/modify data of the object (usually) Bad Nothing really…

Class Example class Car { public: bool AddGas(float gallons); float GetMileage(); // other operations private: float m_currGallons; float m_currMileage; // other data }; Class-name Protection Mechanism Operations Protection Mechanism Data

Struct vs. Class struct DayOfYear { int month; int day; }; // Code from main() DayOfYear july4th; july4th.month = 7; july4th.day = 4; class DayOfYear { public: int m_month; int m_day; }; // Code from main() DayOfYear july4th; july4th.m_month = 7; july4th.m_day = 4;

Class Rules – Coding Standard Class names Always begin with capital letter Use mixed case for phrases General word for class (type) of objects Ex: Car, Boat, Building, DVD, List, Customer, BoxOfDVDs, CollectionOfRecords, … Class data Always begin with m_ Ex: m_fuel, m_title, m_name, … Class operations/methods Ex: AddGas(), Accelerate(), ModifyTitle(), RemoveDVD(), …

Class - DayOfYear // Represents a Day of the Year class DayOfYear { public: void Output(); int m_month; int m_day; }; // Output method – displays a DayOfYear void DayOfYear::Output() cout << m_month << “/” << m_day; } // Code from main() DayOfYear july4th; july4th.m_month = 7; july4th.m_day = 4; july4th.Output();

Method Implementation void DayOfYear::Output() { cout << m_month << “/” << m_day; } Scope Resolution Operator: indicates which class this method is from Class Name Method Name Method Body

Classes // Represents a Day of the Year class DayOfYear { public: void Output(); int m_month; int m_day; }; // Output method – displays a DayOfYear void DayOfYear::Output() cout << m_month << “/” << m_day; } Class Declaration Goes in file ClassName.h Class Definition Goes in file ClassName.cpp

Practice You are working on an Inventory system for a department store Declare a class to represent a Pair of Shoes What data do we need? Assume the only operation will be to display their data to the screen. Implement the Output() method Create a Pair of Shoes Assign the shoes data Print their data using the Output() method

Challenge You are working for the Bookstore… Design Challenge Design a class to represent a textbook What data should it have? What operations should it have? Implementation Challenge I Write the class declaration for a textbook Implementation Challenge II Write the class definition for a textbook You need not implement any of the functions… I just want to see their signatures Use only what we know so far…