COMP2004
Programming Practice
2002 Summer School


Kevin Pulo
School of Information Technologies
University of Sydney

About Me

• Kevin Pulo
• Room: Madsen G88
• Email: kev@cs.usyd.edu.au

• Consultation:
  • 30 mins before each lecture
  • Email to arrange an appointment during consultation times

Textbook

• Accelerated C++ by Koenig & Moo

• The C++ Programming Language by Stroustrup (3rd edition)
• C++ Primer by Lippman (3rd edition)
• Thinking in C++ by Eckel (2nd Edition)

• http://www.accu.org/

Course Information

• Programming Practice
  • so it will involve programming
• Using Development Tools
• Using Software Libraries

• http://www.cs.usyd.edu.au/~kev/pp/
• Friday's lecture: 10am in Carslaw 175
• Tutorials in Services bldg and LG45

Assessment

• Assignment 0 0%
• Assignment 1 10%
• Assignment 2 10%
• Assignment 3 20%
• Final Exam 60%

• Need 45% in the exam and assignment components to pass

Assignment Policy

• Machine and hand marked
  • Follow output instructions exactly
  • Must work on department software/hardware
• Individual work - no groups or copying
• No late assignments without valid paperwork

The C++ Language

• The language we'll be using
• This is not a C course
• The syntax is similar to Java
• A textbook or reference is essential

C++ At Basser

• GNU C++ compiler

g++ -Wall -g -o hello hello.cc

• hello.cc contains the C++ code
• Executable will be named hello
• -Wall turns on all warnings
• -g adds debugging information

A Simple C++ Program

• C++ programs start in a function called main

#include
int main() {
std::cout << "Very simple" << std::endl;
}

• That's a complete C++ program

Variables and Constants

• C++ is strongly typed
• Basic types like Java (int, double, etc)
• Prefix with const for constants

Variables and Constants

• For example

#include
int main() {
const int value = 5;
int result = 4;
result += value;
std::cout << result << std::endl;
}

Enumerated Types

• Types that can only have certain named values
• Very useful for restricted domains
• Each name is an integer internally

enum day_of_week {Sun, Mon, Tue,
Wed, Thu, Fri, Sat};
day_of_week today = Wed;

Functions

• Like Java methods except
  • They are not part of a class
  • No object is used to call them

double halve (int number) {
double result;
result = number / 2.0;
return result;
}

Control Flow

• if, switch, do, while, for - similar to Java
• Some types convertable to bool
• For numeric types:
  • Zero is false
  • Everything else is true

int main() {
int i = 5;
if (i) // equiv to: if (i != 0)
std::cout << i << " is true\n";
}

C++ Programming Style

• C++ is a flexible language
  • as a procedural language
  • as a modular language
  • as an object oriented language
  • as a generic language
• We'll progress through them all during the course

Basic Input

• std::cin is used to read input

#include
int main() {
std::string s;
int i;
double d;
char c;
std::cin >> s >> i >> d >> c;
std::getline(cin, s);
}

Basic Output

• std::cout is used to print output

#include
int main() {
std::string s = "Hello";
int i = 42;
double d = 1.3;
char c = ' ';
std::cout << s << c << i << c << d;
}

Error Output

• std::cerr works like std::cout
• It is used for error messages
• std::cerr will be ignored for marking
• So debugging output should go to std::cerr

#include
int main() {
std::cerr << "Sent to std::cerr\n";
std::cout << "Sent to std::cout\n";
}

Streams

• cin, cout and cerr are just instances of streams
• Streams are used for files as well
• You can even use them for strings
• For now we'll stick to cin and cout...

More on Input

• You can test std::cin to see if input succeeded

#include
int main() {
int x, y;
if (std::cin >> x >> y)
std::cout << "worked" << std::endl;
else
std::cout << "failed" << std::endl;
}

How Input/Output can fail

• No input left - end of file
  • std::cin.eof() will return true
• Wrong data - eg. "abc" is not an int
  • std::cin.bad() will return true
• Hardware or system failure
  • std::cin.fail() will return true
• Call std::cin.clear() to recover
  • The stream can then be used
  • Throws an exception if it fails

Manipulators

• Manipulators are part of stream library
• #include to use them
• They perform operations on the stream
• But are used just like input/output items
• std::endl is an example
  • doesn't need #include
  • outputs '\n' to the stream
  • flushes the stream

setw and setfill

• setw sets minimum output width
• resets to 0 after next output operation
• setfill sets the fill characters
• Fill character defaults to space

std::cout << std::setw(10) << 123;
std::cout << std::setw(5) << std::setfill('#');
std::cout << "hi" << 123;

• Can also use std::cout.width(10)
• And std::cout.fill('#')

setprecision

• Number of digits after the decimal point
• Only applies to floating point output
• Setting to 0 sets to the default

double d = 2.0 / 3.0;
std::cout << d << '\n';
std::cout << setprecision(4) << d << '\n';
std::cout << setprecision(0) << d << '\n';

• Can also use std::cout.precision(4)

Buffered Output

• std::cout is buffered
  • output may be delayed until:
    • the buffer is full
    • std::flush or std::endl is output

• std::cerr is unbuffered
  • outputs immediately

flush

• Defined in #include
• Flushes an unbuffered stream
• Used when you need the output to happen now

std::string name;
std::cout << "Enter name : " << std::flush;
std::cin >> name;

• Can also use std::cout.flush();

std::cerr for debug output

#include
int main() {
std::cout << "A";
function_which_might_crash();
std::cout << "B";
}

std::cout << "A" << std::flush;
std::cout << "A" << std::endl;
std::cerr << "A";




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