CMSC 202

1
CMSC 202

• Lesson 7
• Classes I

2
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 lt Titles.size() i)
• if (Titles.at(i) titleToFind)
• return i
• return Titles.size()

3
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

4
OOP Example

• Driving a car
• Car Data
• 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?

5
OOP Example

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

6
Practice

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

7
Structures

• What about structs?
• Collection of data
• No operations explicitly related
• struct DayOfYear
• int month
• int day
• DayOfYear july4th
• july4th.month 7
• july4th.day 4

No typedef!
Members
8
Structures

• Good
• 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

9
Classes

• Class
• Collection of data and
• Operations on that data
• Object
• Instance of a class
• Examples (on right!)
• Class
• Blueprint, pattern, classification
• Object
• Thing you built, made, constructed

10
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

11
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
12
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

13
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
• Always begin with capital letter
• Ex AddGas(), Accelerate(), ModifyTitle(),
  RemoveDVD(),

14
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 DayOfYearOutput()
• cout ltlt m_month ltlt / ltlt m_day
• // Code from main()
• DayOfYear july4th
• july4th.m_month 7
• july4th.m_day 4

15
Method Implementation

• void DayOfYearOutput()
• cout ltlt m_month
• ltlt / ltlt m_day

Scope Resolution Operator indicates which class
this method is from
Class Name
Method Name
Method Body
16
Classes

• // Represents a Day of the Year
• class DayOfYear
• public
• void Output()
• int m_month
• int m_day
• // Output method displays a DayOfYear
• void DayOfYearOutput()
• cout ltlt m_month ltlt / ltlt m_day

Class Declaration Goes in file ClassName.h
Class Definition Goes in file ClassName.cpp
17
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

18
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