46699 Objectoriented Programming www.andrew.cmu.educourse46699

1
46-699 Object-oriented Programmingwww.andrew.cmu
.edu/course/46-699/

• Ananda Guna
• May 17, 1999 - Lecture 1

guna_at_ cs.cmu.edu School of Computer
Science Carnegie Mellon University
2
Administrivia

• Web page, schedule, text
• TAs Ramu Arunachalam(Pgh) and TBA (NYC)
• Due dates
• Final exam
• Recitation hours
• Software
• MSVC (5.0)
• Metrowerks Codewarrior
• Any other compiler e.g. Borland
• g

3
C Language Background

• Designed on top of C
• C plus OOP features, hence the name C
• Implications
• Almost all of the C features still work
• Some features were simplified, notably the I/O
• Many people claim to program in C, but never
  really use its OOP features - also called a
  better C
• Most compilers support C/C
• The challenge of learning C is in the paradigm
  shift
• Java is based on C

4
Review

• Variables
• Data types
• Primitives int, double, float, char...
• Conditionals (if, if-else, switch)
• Repetition (for, while loops)
• General structure of a C program
• Functions
• Prototypes
• Arguments/parameters
• Call by value

5
Review

• All variables must be declared before use
• Must specify the type of your variable
• Compiler allocates memory
• e.g. int count0 float num1 0.0, num2 0.0
• Always initialize your variables or they contain
  garbage
• Conditionals Used to control execution
• if
• if-else, nested if
• switch

6
Conditionals

• if ( boolean condition true) if(( boolean
  condition true)
• statements if (boolean condition
  true)
• ...
• if ( boolean condition true) if ( boolean
  condition true)
• statements statement
• else else if (boolean condition true)
• statements statements
• else if (...)
• switch(varName) //int varName
• case 1 statements
• break // REQUIRED
• case 2,3,4 statements
• break // REQUIRED
• default debug statement

7
Repetition

• Loops
• for Used when we know the iterations
• while We dont know the exact iterations, but
  we
• know the exit condition
• do while Executes the loop body at least once,
  test is at the bottom
• for ( i0 ilt MAX i)
• //loop body statements
• while (i lt MAX) // assume i is initialized
• //loop body statements //Be sure to update
  loop control variable
• do while
• //loop body statements // Be sure to update loop
  control variable
• while (i lt MAX)

8
Functions

• Units or modules within a program
• Each performs a specific task
• Allow for cleaner programs, promote reuse.
• May be
• system-defined. E.g. the math library functions
• User defined tailored to the application
• Must be called or invoked to be executed
• Prototypes are optional if the function
  implementations appear before the function call.
  However, it is good style to use function
  prototypes
• Can pass arguments to each other
• Can return a value upon exit(Single return
  functions)

9
Scope of a variable

• The segment of the program where it can be seen
• A local variables scope is the block within
  which it is declared plus any nested blocks
• A global variables scope is the entire program
• Lifetime of variables
• Locals die upon exit of a function
• Globals are alive throughout the life of the
  program
• It is bad style to use global varibles. Why?
• Global constants are fine. Why?
• E.g. const int MAX 10 // same as define in C

10
Passing Arguments/parameters

• Call by value
• A copy of the variable is passed
• Call by reference
• The address of the variable is passed
• The called function has direct access to the
  variable
• Arguments
• Must match in number
• Must match in type
• The names do not matter, what matters is the
  order of the arguments, i.e. the first is mapped
  to the first and so on

11
Call by value example

• void print ( int x, float y)
• cout ltlt x ltlt ltlt y ltlt endl
• int
• main()
• int x 10
• float y 22.7
• print(x, y)
• return 0
• // What will be the output for print(y,x)?

10
22.7
10
22.7
12
Call by reference example

• void swap ( int a, int b) // the addresses are
  passed
• int temp
• temp a
• a b // change a gt change x
• b temp // change b gt change y
• cout ltlt a ltlt ltlt b ltlt endl
• int
• main()
• int x 7
• int y 55
• swap(x, y) // Note NO is required here
  unlike C
• cout ltlt x ltlt ltlt y ltlt endl
• return 0

x
y
55
7
13
Arrays

• Group/collection of memory cells
• Each cell must be of the same type
• Declaring an array in C
• const int MAX 30 // define in C
• float stocksPricesMAX

51.5
98.30
0 1
MAX - 1
- Subscript/index begins at zero -
stocksPrices0 is the first element - Every
element is of type float
14
Passing arrays as arguments

• void multArray(float arr, int count)
• // no for array arguments - as in C
• int i
• for ( i 0 i lt count i)
• arri 10.2 // change to the original
  array
• return sum
• //multArray
• // function call
• multArray(arr, count) // assume arr has been
  loaded
• // count is the items in the array
• cout ltlt "\narr0 ltlt setiosflags(ios
  fixedios showpoint)
• ltlt setw(10) ltlt setprecision(2)ltlt arr0
• //output with two decimal places
• // need include ltiomanipgt

15
const array arguments

• void multArray(const float arr, int count)
• // no for array arguments - as in C
• int i
• for ( i 0 i lt count i)
• arri 10.2 // change to the original
  array
• //multArray
• const means the function can use, but may not
  change the array
• The above will throw a compile error - at which
  line?
• Use const to protect against accidently changing
  the array values
• Printing the contents of an array
• Using the array to do some computation

16
Input/output in C

• To read from the console cin
• cin gtgt varName // read into this variable
• cin gtgt varName1 gtgt varName2
• gtgt is called the stream extraction operator
• To print to the console
• cout ltlt varName // dump contents of varName
• cout ltlt varName1 ltlt varName2 ltlt endl
• cout ltlt varName1 varName2 ltlt \n
• ltlt is called the stream insertion operator
• endl end of line (newline plus flush the output
  buffer)
• Much simpler and cleaner than C!
• Sample program

17
File I/O in C

• Sequential Access Files - input
• programmer must create/recognize structure
• ifstream infile(filename, iosin)
• if (!infile) cerrltltFile cannot be open
• exit(1)
• infile gtgt date gtgt maxprice gtgt minprice gtgt close
• File output
• ofstream outfile(filename, iosout)
• outfile ltlt varName1 ltlt varName2 ltlt endl
• if no file then a file is created
• ltlt is called the stream insertion operator
• gtgt is called the stream extraction operator
• Much simpler and cleaner than C!

18
File I/O in C ctd...

• ifstream infile(infile.txt) is ok too
• ofstream outfile(outfile.out) is ok too
• In each case object constructor is called
• logical file physical file
• alternative style
• ofstream outfile
• outfile.open(filename,iosout)
• Reading a file of data to eof
• while (infilegtgtvar1gtgtvar2) process
• while (!infile.eof()) infilegtgtvar1gtgtvar2gtgt

19
File I/O in C ctd...

• You may use include Openfile.h utility
• ifstream infile
• OpenFileForReading(Enter input file , infile)
• ofstream outfile
• OpenFileForWriting(Outfile ? , outfile)
• infile.close()
• outfile.close() // explicit close
• File stream is also destroyed upon leaving the
  scope.

20
Problem Solving Process

• Review
• Algorithm
• Top-down design, stepwise refinement
• Pseudocode
• Flow Chart
• Phases of software development
• Planning figuring out the problem specs
• Design the algorithm, use pseudocode etc
• Code Translate the design into C/Java syntax
• Code review Spell-check your code. Simulate
  the compiler looking for syntax errors
• Compile With a thorough code review, compile
  time is small
• Test/debug

21
System Costs Hardware vs. Software

100
Software
PercentSystemCost
Hardware
1950
2000
Year
courtesy R.Pattis
22
Motivation for Design before Coding

• Analogy Think about how you write a paper
• Problem Statement? Outline? Abstract? Fill in
  details based on the outline? Refine
  sections/paragraphs? How do you proof your paper?
  Do you just type something and watch the
  spell-checker or do you print it out and read it
  for errors?
• Your solution is only as good as your design
• Coding should be low priority compared to design
• If you take short cuts, you will end up spending
  a lot more time on the program.
• Bottom Line There is nothing mysterious about
  coding!!!

23
OOP Versus Non-OOP

• Procedural programming OOP
• - Identify tasks/sub-tasks - Design the
  classes
• - Write procedures - Design the methods
• - Procedures act upon data - Objects
  communicate to solve
• to solve the problem the problem
• - Start with verbs - Start with nouns
• - Data is secondary - Data is primary

24
Problem Solving - OO Design

• Identify the objects
• Identify the operations
• Design the algorithm/decompose into smaller
  chunks
• E.g Compute the amount of tuition to be paid
• Name the objects
• credit hours
• cost per credit hour
• Other costs, such as student activity fee etc
• Any discounts
• Name the operations to be performed
• Addition, subtraction, multiplication
• Algorithm

25
Key Elements of OOP

• Abstraction Focus on the important, ignore the
  details
• e.g. Driving a car
• The interface of the car is what the driver sees
  on the outside, i.e. the dash board, the gas
  pedal and so on.
• The implementation is a detail, e.g. what
  exactly happens when I step on the gas pedal.
• Encapsulation Information hiding
• The details of an object are hidden.
• Users are not allowed to make changes to the
  implementation.
• If there is any change in the implementation, it
  does not affect the users(clients) of the
  interface.
• E.g. A Stack Class has as its interface init,
  push, pop. The implementation may be changed
  from an array to a linked list

26
Key Elements of OOP

• Inheritance
• Building upon what is already defined
• A class can inherit from another class much like
  a child inherits from its parent
• Polymorphism
• Greek for many shapes
• Same name for different things
• Two forms in OOP
• Overloading Functions with the same name
• Over-riding A child class redefining its
  parents functions

27
OOP Terminology

• Program objects cooperating to solve a problem
• Properties of an object
• State gt data gt nouns
• Operations gt behavior gt verbs
• Identity

28
Object Examples

• Example 1 An electronic mailbox
• States full or empty
• Operations add, delete ...
• Identity any 2 mailboxes will be different
• e.g. hou and aj29 each have a mail box
• Example 2 traffic signal

29
Object Components

• An object is composed of both data and
• Operations which can act upon the data

Operations
Data
In a C object Operations gt member
functions (methods) Data gt data members
30
Classes

• Class
• A collection of related objects.
• Instance of a class object
• Factory with blueprints/instructions to build
  gadgets
• Objects the gadgets the factory makes.
• Example
• Class checkingaccount
• Objects minnieCheckacct, mickeyCheckacct

31
Example OOP Design

• Problem write a program to simulate an ATM
• Data (nouns)
• Account name
• Account balance
• ...
• Operations /behavior(verbs)
• Deposit
• Withdraw
• Inquire balance
• ...

32
Problem ( Elevator Control Problem)

• Simulation of an elevator control system. 20
  floors , 4 elevators
• 1. Identify the data objects
• 2. Identify the data operations
• 3. Solve the problem
• Read Chapter 6-7 (Dietel Text)
• Any questions Email guna_at_cs.cmu.edu