Week 01

COMP2521 17s2 ... Computing 2

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Course Goals

2/36

COMP1511 ...

• gets you thinking like a programmer
• solving problems by developing programs
• expressing your ideas in the C language

• gets you thinking like a computer scientist
• knowing fundamental techniques/structures
• able to reason about applicability/effectiveness
• able to analyse behaviour/correctness of programs

COMP1511 vs COMP2521

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COMP1511 ...

... COMP1511 vs COMP2521

4/36

COMP2521 ...
 

Thinking like a Scientist

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Course Context

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Pre-conditions

7/36

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

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

Post-conditions

8/36

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

• analyse performance characteristics of algorithms
• measure performance behaviour of programs
• choose/develop effective data structures (DS)
• choose/develop algorithms (A) on these DS
• package a set of DS+A as an abstract data type
• develop and maintain 9999-line C programs

Data Structure Viewpoint

9/36

COMP1511 considered ...

... Data Structure Viewpoint

10/36

COMP2521 also considers ...

COMP2521 Themes

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Major themes ...

1. Analysis: correctness, performance, usability
2. ADTs: sets, lists, trees, graphs, dictionaries
3. Operations: building, sorting, searching, traversing

For algorithms: complexity analysis, performance analysis

COMP2521 on the Web

12/36

Primary entry point is WebCMS

   http://webcms3.cse.unsw.edu.au/COMP2521/17s2/

... COMP2521 on the Web

13/36

Most material on WebCMS is publically readable.

Login to WebCMS is via zID/zPass, and is needed for

• polls, comments/forums, forming groups, ...

Submit work via give   (either in WebCMS or on cmd line)

Check marks via sturec   (either in WebCMS or on cmd line)

Credits for Material

14/36

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

COMP2521 material is prepared by John Shepherd, and ideas are drawn from

• notes by Aleks Ignjatovic (COMP2011 2005)
• slides by Manuel Chakravarty (COMP1927 08s1)
• lectures by Richard Buckland (COMP1927 09s2)
• slides by Gabrielle Keller (COMP1927 12s2)
• slides and books by Robert Sedgewick

Textbook

15/36

Textbook is a "double-header"

• Algorithms in C, Parts 1-4, Robert Sedgewick
• Algorithms in C, Part 5, Robert Sedgewick

       

Good books, useful beyond COMP2521, but code style .....

Lectures

16/36

Three scheduled hours: Tuesday 10-11am, Wednesday 10-12noon

Lectures will contain ...

• summary of content   (read text/notesin advance)
• problem-solving exercises, hopefully, with lots of input from you.

  But without any "background noise".

  ---

  Tutes and Labs

  17/36

  Tutorials ...

  • as in COMP1511  (including code reviews)
  • analysis/design practice; clarify lecture material

  Labs ...

  • small(ish) implementation tasks, done in pairs
  • give skills practice (leading on to assignments/exam)

  Tutes/labs run weeks 2 to 13

  Exercises for Week X available in Week X-1

  ---

  ... Tutes and Labs

  18/36

  Lab exercises contribute 5% to overall mark.

  The lab exercises for Week X must be

  • submitted before Sunday at end of week X
  • demonstrated to tutor during Week X lab
    OR, demonstrated at the start of Week X+1 lab

  Total mark for all the labs is greater than 5 (and they are scaled to 5).

  ---

  Practical Lab Exams

  19/36

  Two practical lab exams ...

  • first practical lab exam during week-5 lab
  • second practical lab exam during week-12 lab

  Two practical lab exams contribute 12% towards final mark. Total mark for all the practical lab exams is greater than 12 (and they are scaled to 12).

  ---

  Assignments

  20/36

  Two assignments ...

  • Ass1:   9% towards final mark,   (due in week-5 or 6, may chage)
  • Ass2:   14% towards final mark,   (due in week-11 or 12, may change)

  Two assignments contribute 23% towards final mark, subject to the conditions outlined in the section named "Course Assessment".

  Total mark for the assignments is greater than 23 (and they are scaled to 23).

Late penalties apply if you miss the deadline.

Good time management avoids late penalties!

Plagiarism

21/36

Final Exam

22/36

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

Held in CSE labs   (must know lab environment)

On-line documentation available in exam:

• C quick reference;   Unix programmers Manual

Format:

• some programming exercises   (Prac)
• some descriptive/analytical questions   (Theory)

How to pass?   Practice, practice, practice, ...

Supplementary Exams

23/36

Supplementary Exams are only available to students who

• do not attend the exam
• have a documented reason for not attending

We may also offer Supplementary Prac Exams to students who

• failed final exam by messing up the Prac
• put in a "satisfactory effort" in the rest of course
• gives you maximum 50% for final mark

Course Assessment

24/36

labs                = mark for lab exercises         (out of  5)
ass1                = mark for assignment 1          (out of  9)
ass2                = mark for assignment 2          (out of 14)
practicalLabExams   = mark for practicalLabExams     (out of 12)
finalExam           = finalPracExam (36) + finalTheoryExam (24)          (out of 60)

mark      = labs + assignmentMarks + practicalLabExams + finalExam
grade     = HD|DN|CR|PS  if mark >= 50 && okALL
          = FL           if mark <  50 
          = UF           if mark >= 50 && !okALL



okALL is calculated as below:
okPracticalLabExams = (practicalLabExams >= 8/12)      
okFinalPracExam     = (finalPracExam > 18/36 )      
okALL               = okPracticalLabExams && okFinalPracExam  



assignmentMarks is calculated as below:
assignmentMarks     = ass1 + ass2
assPerc             = assignmentMarks in percentages (out of 100)
pracExamPerc        = finalPracExam in percentages (out of 100)
if( assPerc > pracExamPerc ) {
    // harmonic mean of assPerc and pracExamPerc
    adjusted_assPerc = (2 * assPerc * pracExamPerc)  / (assPerc + pracExamPerc)
    assignmentMarks  = 23 * (adjusted_assPerc / 100)
}

In other words, if you don't learn how to program by doing the prac work yourself, you'll score poorly in the finalPracExam, resulting in reduced assignment marks and making it very difficult for you to pass the course.

For more clarification on adjusted_assPerc (or why you should do the prac work yourself!), see the following table:

.

Summary

25/36

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
• able to analyse/justify your choices
• producing a better end-product
• ultimately, enjoying the programming process

C vs COMP1511 vs COMP2521

COMP1511 Style

27/36

Required use of a restricted subset of C:

• layout, use of brackets (always)
• use only if and while
• no side-effects in expressions
• no conditional expressions
• all functions have one return statement

COMP2521 Style

28/36

Extends the range of allowed constructs:

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

... COMP2521 Style

29/36

More allowed C constructs ...

• can use assignment statements in expressions
  • but you should continue to avoid other kinds of side-effects
• can use conditional expressions
  • but use   x = c ? e1 : e2   with care
• functions may have multiple return statements
  • use very sparingly, primarily for error handling

... COMP2521 Style

30/36

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

Switch-statements

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switch encapsulates a common selection:

if (v == C1) {
   S1;
} else if (v == C2) {
   S2;
}
...
else if (v == Cn) {
   Sn;
}
else {
   Sn+1;
}

... Switch-statements

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Multi-way if becomes:

switch (v) {
case C1:
   S1; break;
case C2:
   S2; break;
...
case Cn:
   Sn; break;
default:
   Sn+1;
}

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

Exercise 1: Displaying Months

33/36

Write a function monthName(int) that

• accepts a month number 1=Jan ... 12=Dec
• returns a string containing the month name
• assume that the string will be read-only
• use a switch to decide on the month

For-loops

34/36

for encapsulates a common loop pattern:

init;
while (cont) {
   do something;
   incr;
}

as

for (init; cont; incr)
   do something;

... For-loops

35/36

COMP1511 (while) version

sum = 0;
i = 1;
while (i < 10) {
    sum = sum + i;
    i++;
}

COMP2521 (for) version

sum = 0;
for (i = 0; i < 10; i++)
    sum += i;

Exercise 2: Sequence program, using for

36/36

Write a program that prints integer sequences (one per line):

• seqq 10   prints   1 2 3 4 5 6 7 8 9 10
• seqq 5 10   prints   5 6 7 8 9 10
• seqq 10 1   prints   10 9 8 7 6 5 4 3 2 1
• seqq 1 3 10   prints   1 4 7 10
• seqq 1 3 11   prints   1 4 7 10
• seqq -3   prints   1 0 -1 -2 -3
• seqq 1 -3 10   gives an error

void seq(int start, int step, int finish) {...}

main checks errors and sets up args for seq()

Produced: 24 Jul 2017