Week 01 (Monday)

COMP1921 16s2 Computing 1B

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( Introduction to (C) Programming (continued) )

Ashesh Mahidadia

Web Site:   http://www.cse.unsw.edu.au/~cs1921/16s2/

COMP1921 16s2 Course Convenor

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Name:		Ashesh Mahidadia
Email:		ashesh@cse.unsw.edu.au
Research:		Artificial Intelligence, Machine Learning, Knowledge based Systems

COMP1921 16s2 Tutorials and Labs

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Name:		Mei Cheng Whale
Phone:		9385 5683
Email:		meicheng@cse.unsw.edu.au

Course Aims

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This course aims to extend your programming knowledge

• build on the foundation from COMP1911
• deepen your understanding of C program execution
• introduce useful (dynamic) data structures
• introduce useful algorithmic approaches

• you can solve moderately complex problems in C
• you could take more CS courses if interested
• you can write programs to solve problems at work

Access to Course Material

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All course information is placed on the course website:

• http://www.cse.unsw.edu.au/~cs1921/16s2/

Slides/Tutorials/Labs are publically readable.

If you need to post/submit/etc, you need to login.

Inputs

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At the start of this course you should be able to:

• produce a correct C program from a simple specification
• understand the state-based model of computation
  (variables, assignment, parameters, scope(?))
• use fundamental C data structures
  (char, int, float, arrays, pointers(?))
• use fundamental control structures
  (sequence, selection (if), iteration (for, while))
• use abstraction via function declarations
• fix simple bugs in incorrect programs

Exercise: C revision

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On a piece of paper, write a C program that:

• prints the first ten integers (1..10)
• one integer per line with no spaces

• all #include's needed to compile
• appropriate return status

Outputs

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At the end of this course you should be able to:

• work from a well-defined problem statement
• develop correct, robust software to solve problem
• choose effective data structures to solve problem
• choose algorithms on these data structures
• provide evidence that program is reliable/efficient
• develop and maintain 999-line C software systems

Schedule

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Week		Lectures		Ch		Notes
02		Intro, C revision, C execution model		1-6		First tute/lab
03		Single-, multi-dimensional arrays & pointers		7		-
04		Testing, debugging, performance		-		-
05		Structured data types		8		Quiz 1
06		Dynamic memory allocation		10		-
07		Linked lists		10		Assignment released
08		Stacks and queues		10		-
09		Abstract data types		10		Quiz 2
10		Binary trees		10		-
11		Random numbers, File operations		11		-
12		Sorting algorithms		12		-
13		Problem solving strategies		9		Final tute/lab, Assignment due

Credits for Material

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Always give credit when you use someone else's work.

Ideas for the COMP1921 material are drawn from

• slides and notes by Michael Thielscher, John Shepherd and Salil Kalhere
• Alistair Moffat's book

Resources

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Textbook:

• Alistair Moffat
  Programming, Problem Solving, and Abstraction with C
  Pearson Educational, Australia, Revised edition 2013, ISBN 978-1-48-601097-4

• Brian W. Kernighan and Dennis M. Ritchie
  The C Programming Language, 2nd edition
  Prentice Hall, USA, 1988, ISBN 0-13-110370-9
• Paul Davies
  The Indispensable Guide to C
  Addison Wesley, England, 1995, ISBN 0-201-62438-9

Lectures

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Lectures will:

• present a brief overview of theory
• demonstrate problem-solving methods
• give practical demonstrations

Lecture slides will be made available before lecture.

Feel free to ask questions, but No Idle Chatting.

Tutorials

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Tutorials aim to:

• clarify any problems with lecture material
• work through exercises related to lecture topics
• give practice with design skills   (think before coding)

Tutorials start this week (Week 2)

Tutorial and lab exercises available on web Thursday the week before

... Tutorials

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To get the best out of tutorials

• attempt the problems yourself, before the tute
• if you understand OK and get feasible answer, fine

• you aren't sure your answer is feasible/correct
• you don't understand a question or how to solve it

To get the most from tutorials ... participate

Lab Classes

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Each tutorial is followed by a two-hour lab class.

Lab exercises aim to build skills that will help you to

• complete the assignment work
• pass the final exam

Each lab exercise is a small implementation/analysis task.

Do them yourself!   and   Don't fall behind!

... Lab Classes

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Lab exercises contribute 10% to overall mark.

In order to get a mark, lab exercise for Week X must be

• submitted in the lab and demonstrated to your tutor
• or submitted by Sunday 11:59pm at end of week X
  • and demonstrated in your lab in week X+1

You can work in teams of two for the lab exercises

• submit the same solutions
• both of you must be able to demonstrate and explain all programs by the team
• new teams at least twice: after weeks 4 and 8

Quizzes

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There are 2 'mid-session' quizzes: one each in weeks 5 and 9.

• Held instead of the lab in that week, in the same computer laboratory of course
• Consist entirely of programming exercises and could include producing test cases
• The concise C-reference guide will always be available

Assignment

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The assignment gives you experience applying tools/techniques
(but to a larger programming problem than the lab exercises)

The assignment will be carried out individually.

The assignment is due at 11:59pm, Friday, Week 13.

15% penalty will be applied to the maximum mark for every 24 hours late after the deadline.

• 1 day late: mark is capped to 85% of the maximum possible mark
• 2 days late: mark is capped to 70% of the maximum possible mark
• 3 days late: mark is capped to 55% of the maximum possible mark
• ...

The assignment contributes 15% to overall mark.

... Assignment

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Advice on doing the assignments:

They always take longer than you expect.

Don't leave them to the last minute.

Organising your time → no late penalty.

If you do leave them to the last minute:

• take the late penalty rather than copying

Plagiarism

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You attempt Labs and Assignments unsupervised ...

Plagiarism = submitting someone else's work as your own.

We get very annoyed by people who plagiarise.

Plagiarism will be checked for and punished.

You must be able to demonstrate and explain programs to your tutor.

It's not clever to try to get through this course by copying.

Most of you will be doing more computing in your own schools.

... Plagiarism

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We frown on plagiarism BUT ...

• we talk about code re-use ("don't re-invent the wheel")

In some places, we will allow it

• BUT this will be very clearly stated
• you must attribute the source of the code

Final Exam

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3-hour on-line exam during the exam period.

Held in CSE labs   (must know lab environment)

Some on-line documentation will be available.

Format:

• some programming exercises
• some multiple-choice questions
• some descriptive/analytical questions

... Final Exam

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How to pass the Exam:

• do the Lab exercises yourself
• do the Assignment yourself
• practise programming outside classes
• treat each Lab class like a mini Exam?
• understand the Tutorial questions
• read the lecture notes

Supplementary Exams

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You can apply formally for special consideration

• a supplementary examination may or may not be granted
• a supplementary examination will not be granted if you cannot pass the exam
• a supplementary examination is typically more difficult than the original examination

• you are making a statement that you are "fit and healthy enough"
• it is your only chance to pass (i.e. no second chances)

Assessment Summary

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labs   = mark for labs        (out of 10)
quiz1  = mark for quiz 1      (out of 5)
quiz2  = mark for quiz 2      (out of 15)
ass    = mark for assignment  (out of 15)
exam_w = mark for written part of final exam (out of 20)
exam_c = mark for coding part of final exam  (out of 35)

mark   = labs + quiz1 + quiz2 + ass + exam_w + exam_c

To pass the course, you must achieve:

• at least 27/55 for [exam_c + quiz1 + quiz2]
• at least 50/100 overall

How to Pass this Course

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Programming is a skill that improves with practice.

The more you practise, the easier will be labs/quizzes/assignment/exam.

Don't restrict practice to lab times and two days before assignment due.

It also helps to pay attention in lectures and tutorials.

Summary

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The goal is for you to become a better programmer

• more confident in your own ability
• with an expanded set of tools to draw on
• producing a better end-product
• ultimately, enjoying the programming process

Exercise: Integers between N and M

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Consider the program to print the first 10 integers.

Modify it so that can ...

• print all integers between M and N
• accept M and N as a command-line argument
• complain if M or N isn't an integer

Use sscanf() to create an integer from a string. Example:

int n;
sscanf(argv[1], "%d", &n);

C Language/Style

COMP1921 Style

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Extends the range of allowed constructs:

• layout: consistent indentation still required
• use of brackets:
  • always, even for single statement blocks
  • put function start bracket on line after function header
• can use all of these C control structures:
  • if, switch, while, for, break, continue

... COMP1921 Style

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Good: gives you more freedom and power

• more choice in how you express programs
• can write code which is more concise (simpler)

Bad: gives you more freedom and power

• can write code which is more cryptic
• can lead to incomprehensible, unmaintainable code

Sidetrack: Obfuscated Code

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C has a reputation for allowing obscure code, leading to ...

The International Obfuscated C Code Contest

• Run each year since 1984
• Goal is to produce
  • a working C program
  • whose appearance is obscure
  • whose functionality unfathomable
• Web site: www.ioccc.org
• 100's of examples of bizarre C code
  (understand these → you are a C master)

... Sidetrack: Obfuscated Code

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Most artistic code (Eric Marshall, 1986)

                                                   extern int
                                                       errno
                                                         ;char
                                                            grrr
                             ;main(                           r,
  argv, argc )            int    argc                           ,
   r        ;           char *argv[];{int                     P( );
#define x  int i,       j,cc[4];printf("      choo choo\n"     ) ;
x  ;if    (P(  !        i              )        |  cc[  !      j ]
&  P(j    )>2  ?        j              :        i  ){*  argv[i++ +!-i]
;              for    (i=              0;;    i++                   );
_exit(argv[argc- 2    / cc[1*argc]|-1<4 ]    ) ;printf("%d",P(""));}}
  P  (    a  )   char a   ;  {    a  ;   while(    a  >      "  B   "
  /* -    by E            ricM    arsh             all-      */);    }

... Sidetrack: Obfuscated Code

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Just plain obscure (Ed Lycklama, 1985)

#define o define
#o ___o write
#o ooo (unsigned)
#o o_o_ 1
#o _o_ char
#o _oo goto
#o _oo_ read
#o o_o for
#o o_ main
#o o__ if
#o oo_ 0
#o _o(_,__,___)(void)___o(_,__,ooo(___))
#o __o (o_o_<<((o_o_<<(o_o_<<o_o_))+(o_o_<<o_o_)))+(o_o_<<(o_o_<<(o_o_<<o_o_)))
o_(){_o_ _=oo_,__,___,____[__o];_oo ______;_____:___=__o-o_o_; _______:
_o(o_o_,____,__=(_-o_o_<___?_-o_o_:___));o_o(;__;_o(o_o_,"\b",o_o_),__--);
_o(o_o_," ",o_o_);o__(--___)_oo _______;_o(o_o_,"\n",o_o_);______:o__(_=_oo_(
oo_,____,__o))_oo _____;}

Switch-statements

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switch encapsulates a common type of selection:

if (var == Constant1) {
   some statements1;
} else if (var == Constant2) {
   some statements2;
}
...
else if (var == Constantn) {
   some statementsn;
}
else {
   some statementsn+1;
}

... Switch-statements

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Multi-way if becomes:

switch (var) {
case Constant1:
   some statements1;
   break;
case Constant2:
   some statements2;
   break;
...
case Constantn:
   some statementsn;
   break;
default:
   some statementsn+1;
}

Note break is critical; if not present, falls through to next case.

Exercise: If / Switch

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Convert the following if to a switch:

if (n == 1) {
	printf("One\n");
} else if (n == 2) {
	printf("Two\n");
} else if (n == 3) {
	printf("Three\n");
} else if (n >= 4 && n <= 9) {
	printf("Real Big\n");
} else {
	printf("Huh?\n");
}

Exercise: Count lines in stdin

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Write a program that

• reads text from its standard input
• counts the number of lines in the text
• displays this as a single number
• a line is anything that ends with '\n'

Programming Tools

Programming Tools

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Documentation   (man, info)

• descriptions of Unix tools and C libraries

• entering/modifying text (incl. source code)
• assistance for code: syntax highlight, auto-indent, ...

• convert source code to executable (x.c → a.out)
• options for debugging, optimising, profiling, ...

... Programming Tools

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Version control   (cvs, svn, ...)

• manages multiple versions of source code

• specifies dependencies among code modules
• controls building of software from these modules

• combine the above functionalites via a GUI
• additional features: e.g. search for definitions

... Programming Tools

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Debuggers   (gdb, ddd, lldb,...)

• monitor/control execution of programs
• trace values of variables, observe data structures
• provide info; you need to make diagnosis

• measures execution time of individual functions
• allows you find performance "hot spots"

Produced: 11 Aug 2016