46-699 Object-oriented Programming andrew.cmu/course/46-699/

46-699 Object-oriented Programmingwww.andrew.cmu.edu/course/46-699/ Ananda Guna May 17, 1999 - Lecture #1 guna@ cs.cmu.edu School of Computer Science Carnegie Mellon University

Administrivia • Web page, schedule, text • TA’s: 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++

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++

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

Review • All variables must be declared before use • Must specify the type of your variable • Compiler allocates memory • e.g. int count=0; 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

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; }

Repetition • Loops • for: Used when we know the # iterations • while: We don’t 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 ( i=0; i< MAX; i++){ //loop body statements; } • while (i < 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 < MAX);

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)

Scope of a variable • The segment of the program where it can be “seen” • A local variable’s scope is the block within which it is declared plus any nested blocks • A global variable’s 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

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

Call by value example void print ( int x, float y){ cout << x << “ “ << y << 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

Call by reference example void swap ( int& a, int& b){ // the addresses are passed int temp; temp = a; a = b; // change a ==> change x b = temp; // change b ==> change y cout << a << “ “ << b << endl; } int main(){ int x = 7; int y= 55; swap(x, y); // Note: NO & is required here unlike C cout << x << “ “ << y << endl; return 0; } x y 7 55

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 stocksPrices[MAX]; 51.5 98.30 [0] [1] [MAX - 1] - Subscript/index begins at zero - stocksPrices[0] is the first element - Every element is of type float

Passing arrays as arguments void multArray(float arr[], int count){ // no & for array arguments - as in C int i; for ( i = 0; i < count; i++){ arr[i] *= 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 << "\narr[0] ” << setiosflags(ios :: fixed|ios ::showpoint) << setw(10) << setprecision(2)<< arr[0]; //output with two decimal places // need #include <iomanip>

const array arguments void multArray(const float arr[], int count){ // no & for array arguments - as in C int i; for ( i = 0; i < count; i++){ arr[i] *= 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

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

File I/O in C++ • Sequential Access Files - input • programmer must create/recognize structure • ifstream infile(filename, ios::in) • if (!infile) { cerr<<“File cannot be open”; • exit(1);} • infile >> date >> maxprice >> minprice >> close; • File output • ofstream outfile(filename, ios::out) • outfile << varName1 << varName2 << endl; • if no file then a file is created • << is called the stream insertion operator • >> is called the stream extraction operator • Much simpler and cleaner than C!

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”,ios::out); • Reading a file of data to eof • while (infile>>var1>>var2…) { process} • while (!infile.eof()) { infile>>var1>>var2>>…}

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.

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

System Costs: Hardware vs. Software* 100% Software PercentSystemCost Hardware 1950 2000 Year * courtesy R.Pattis

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!!!

OOP Versus Non-OOP • Procedural programmingOOP - 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

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

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

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 parent’s functions

OOP Terminology • Program = objects cooperating to solve a problem • Properties of an object: • State ==> data ==> nouns • Operations ==> behavior ==> verbs • Identity

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

Object Components • An object is composed of both data and Operations which can act upon the data Operations Data • In a C++ object: • Operations ==> member functions (methods) • Data ==> data members

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

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

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@cs.cmu.edu

46-699 Object-oriented Programming andrew.cmu/course/46-699/