Object Orientated Systems

1
Object Orientated Systems
(A new beginning)

• James Goulding
• A10 jog_at_cs.nott.ac.uk
• Chris Coleman
• A09 cqc_at_cs.nott.ac.uk

2
Your new C Obsessed Life

• Lectures
• Monday 12.00 (LT1)
• Friday 11.00 (C33)
• Labs
• Monday 2.00 4.00 (A31)
• Thursday 9.00 11.00 (A31) (starting 3rd Feb)
• Surgery Sessions - (1 hour drop in slots)
• Times to be announced
• Theres more
• Catch up classes if required.
• Discussion board on course website

3
Assessment

• 2 Courseworks (50)
• 1) 20 - 21st Feb ?17th March
• 2) 30 - 14th March ? 5th May
• Exam (50)
• Similar to ICP in style, more details to follow.

4
Web Page Book List

• Main Course Web Page is at
• www.cs.nott.ac.uk/cqc/OOS
• The recommended texts for CFJ are
• C The Complete Reference 25
• (Herbert Schildt McGraw Hill)
• Or
• The C Programming Language50
• (Bjarne Stroustrup - Addison-Wesley)

5
Handy Website

• The C FAQ Lite
• Translated into many languages, including
• French, Russian, Chinese and even English.
• http//www.parashift.com/c-faq-lite/
• VAST amounts of knowledge and tips in here
• Links will appear to sections of it in the notes
  from time to time for extra reading.

6
Here we go.

• Course is split up into 5 sections
• Java Bashing (In a minute) - 1 Lecture
• Basic C - 4 Lectures
• OO and C - 5 Lectures
• Advanced C and the STL 7 Lectures
• Algorithms and Data Structures 4 Lectures
• Revision Lecture

7
What is C?

• Low Level Languages
• - Machine Code, Assembler
• Mid Level Languages
• - Java, C, Pascal, C
• High Level Languages
• - Visual Basic, Symantec Cafe, Delphi

8
A really brief C history

• (1958) Algol Created The first ever high-level
  structured language with a systematic syntax.
• (1969) UNIX created using BCPL (Basic Combined
  Programming Language)
• B created by Ken Thompson, as a replacement for
  BCPL.
• (1970) Pascal, a very formal and well defined
  language established as the successor to Algol
• (1973) C completed, and released as the successor
  to B, giving the user control of data types.
• (1979) Bjarne Stroustrup begins work on
  C-with-Classes, an Object Orientated version of
  C.

9
Where does C come from?
BJARNEY
10
Progression of C

• (1983) C-with-Classes redesigned and released as
  C
• (1985) First mass release of C compilers.
• (1988) Lots of versions of C begin to emerge.
• (1989) ANSI/ISO standardisation of C begins
• (1999) and a decade later finally approved.
• (1995) Java goes public, viewed by many as being
  the successor to C.
• (2004) Java, the language of the web, has taken
  over the world, and C is becoming a dead
  language..

11
Progression of C

• .only it hasnt.
• (else youd not be learning about it now)

12
What is C used for?

• Word Processors
• Operating systems
• Web Browsers
• Databases
• Spreadsheets, Mail Software.
• Games, Music Software.
• .basically everything
• Almost everything you see is written using C.
  Even new C compilers are written using the old
  ones.

13
So why all this Java stuff then?

• Java is an important language.
• It's easy to learn.
• Its portable.
• It provides meaningful errors (usually).
• It removed complications like templates and
  pointers.
• Added garbage collection (aka Memory management)
• Added multithreading
• Added GUI libraries
• Protected the user from making many errors.

14
So why all this Java stuff then?

• Some see the Recipe for Java as
• Take C.
• Subtract functionality, speed and power.
• Box stuff in classes that take up 10 times the
  space that they have to.
• Add bugs to every implementation

15
Compilers vs Interpreters
Storage
COMPILED
INTERPRETED
CPU/Memory
16
Compilers vs Interpreters

• Compiled (eg C)
• Runs faster
• Typically has more functionality
• Easier to Optimise
• More instructions available
• Best choice for complex programs that need to be
  fast
• Interpreted (e.g. PHP, Perl)
• Slower, but often easier to develop
• Allows runtime Flexibility
• More appropriate for use on the web

17
The Java Model
Storage
CPU/Memory
18
The Java Model

• Java is unique because it is both compiled and
  interpreted.
• Java is compiled into byte code, and then
  interpreted by the virtual machine.
• Great advantage of Java is that the code can be
  compiled once and then run on any other type of
  machine.
• Except it cant necessarily, because of the
  variability among java interpreters, and their
  implementations on different platforms.

19
C Disadvantages

• It does not protect you from making mistakes.
• The power it offers the programmer makes it very
  easy to crash your PC.
• C with its many concepts and possibilities has
  a steep learning curve.
• extensive use of some C concepts can very
  quickly make C programs very complicated to
  read initially.
• Shortcuts that it offers can often make it
  completely unreadable, eg
• if (hrhr!12)(hrlt12)?(P "d ",hr))(P "d
  ",hr-12))
• Dont panic!!!

20
C Advantages

• C is very powerful.
• It is very efficient.
• It is extremely fast.
• Everything can be written using C.
• As you learn C, you learn how computers work on
  the inside.
• Once you learn C well, you will not want to
  program in Java.

21
C for Java Programmers
(The Real Beginning)

• Section 1
• Basic C

22
C files

• Traditionally C programs use the file extension
  .c and C programs the extension .cpp
• C is essentially a subset of C, so you could
  use a C compiler to run a C program. The two
  languages are extremely similar BUT NOT THE
  SAME! We are learning C NOT C.

23
C Compilers

• DO NOT USE MS VISUAL C at home or in the labs.
  It isnt really C.
• In the labs, and for the coursework we will be
  using a UNIX based compiler called gcc.
• Open source standard C compiler
• Produced by the Free Software Foundation
• Just because its free doesnt mean its bad
• Strictly ANSI standards compliant
• Command Line based
• Very versatile

24
C Compilers In the Lab

• There are 2 versions of gcc installed on scarlet.
  2.95 and 3.4.
• 2.95 is old and past it but the default on
  scarlet.
• 3.4.3 is shiny and new
• To make 3.4 your default
• logon to scarlet and type
• scarlet wget http//www.cs.nott.ac.uk/cqc/OOS/gc
  c_setup-0.1.sh
• scarlet chmod ux gcc_setup-0.1.sh
• scarlet ./gcc_setup-0.1.sh
• scarlet g --version
• Check version is 3.4.3

25
C Compilers At home

• Linux You almost certainly have gcc somewhere
  on your system.
• Win32 You almost certainly dont have it.
• MinGW (Minimalist GNU)
• A port of GCC for windows.
• 2 good ways to use MinGW DevC or with MSYS
  (both front ends)
• DevC is a full IDE with gcc as the compiler
  backend
• http//www.bloodshed.net/dev/index.html
• MSYS is a UNIX like shell that runs on windows
• http//www.mingw.org/

26
C from home

• Bit of a pain setting up on windows at home.
• You should always be testing on the university
  C version.
• (This is what we mark courseworks on)
• The answer is to ssh or telnet in over the
  internet
• in windows select run from the windows menu, and
  type
• telnet scarlet.cs.nott.ac.uk
• Editing your files is very difficult over telnet
  or ssh so better to use ftp (ftp//scarlet.cs.nott
  .ac.uk) to transfer your files. This will be
  explained again in an exercise sheet.

27
Anatomy of a Program

• The project source for a C program
• include ltiostreamgt
• using namespace std
• int main()
• cout ltlt No more Big Brother. Please. ltlt endl
• return EXIT_SUCCESS

28
Very Little to Learn

• include is the preprocessor command used, to
  allow the program access to more functions, in
  this case the cout command, from the C Standard
  Library iostream.
• There is a little more to include, but thatll
  do for now.
• include is almost always used because the core
  C language has hardly any reserved words

29
Initial Similarities (C vs Java)

• C is strongly typed.
• C can be Object Orientated.
• C uses almost the same variable types as Java.
• C and Java have the same rules for Identifier
  Types
• The Good The Bad
• count 1count
• ronnie_size Eric Prydz
• twentyFour 13

30
Comments in Code

• Comments are also identical to Java.
• // this is a comment on one line
• / this is a comment
• and it is on more than
• one line /
• No special javadoc style commenting as part of
  the language, but external utilities exist.
• Eg. doxygen

31
C Techniques

• Variables
• Operators
• Decisions
• Loops

32
1. C Variables Scope

• Variables, can be declared anywhere in the
  program.
• Within methods, classes, or outside them both in
  the global scope
• However they are only visible to the program
  within the block of code in which they are
  defined.
• int main()
• int x 4
• if (x gt 3)
• int y 3
• cout ltlt x is ltlt x ltlt endl
• cout ltlt y is ltlt y ltlt endl
• cout ltlt y is ltlt y ltlt endl
• return EXIT_SUCCESS

ERROR
33
C Variable Types

• There are various variable types available, some
  are shown below
• Unlike Java, their range is compiler dependant,
  so the values above are minimum values set by the
  ANSI standard.
• Each compiler defines the range in the ltclimitsgt
  header file

34
2. C Operators

• Operators are similar to in Java
• Addition x y z
• Subtraction x y z
• Multiplication x y z
• Real number division x y / 3.14
• Integer division x y / 10
• Logical AND if (x1 y2)
• Logical OR if (x1 y2)
• Logical NOT if (!x)

35
C Operators

• More Identical operators
• Equal to if (x10)
• Not equal to if (x!10)
• Less than if (xlt10)
• Greater than if (xgt10)
• Less than / equal to if (xlt10)
• Greater than / equal to if (xgt10)

36
C Operators

• The increment and decrement operators
• Increment x or x
• Decrement x- or -x
• Shorthand Assignments x3 (multiply x by
  3) x5 (add 5 to x)
• x-10 (subtract 10 from 6)
• x/2 (halve x)

37
C Operators - prefix / postfix

• There is a subtle difference between x and x
  when used in an expression.
• x will increment the variable before it does
  anything else with it, x will increment after
  the evaluation of the expression.
• Only in the 1st case is y set to 11.
• Prefix is preferable if simply incrementing a
  value.

x 10 y x
x 10 y x
y 10 y y



Here y is set to 11
Now y is set to 10
But here y is still 10
38
Simple Type Conversions

• When variables of one type are mixed with another
  Type Conversion occurs. This is not impossible in
  Java (where casting is needed), and would cause
  an error.
• int main()
• int x
• char ch
• float f
• ch x
• x f
• f x

If x is between 0 and 255, ch and x would get the
exact same values. Other wise ch would only
reflect the first 8 bits of x.


Here x will be given the bits that represent the
non fractional part of f.
Here f will be a decimal form of x
39
Different Outlooks

• This highlights the differing outlooks of the
  languages
• C assumes youre Clever. It gives the
  programmer masses of power. And as Spiderman
  says, with power comes great responsibility.
• Whereas, Java assumes youre a desk monkey.

40
Casting in C - Basics

• You can force an expression to be of a specific
  type by using casting. The general form of a cast
  is
• (type) expression
• Where type is a valid data type. For example to
  make sure that the expression x/2 evaluates to
  type float, write
• (float)(x/2)
• Without the cast only an integer division would
  have been performed.

41
3. Decisions

• The structure of an if statement in C (again
  stolen by Java) is as follows

42
Nested If Statements

• Again, the same as Java

• int main()
• int winner -1
• cout ltlt and the Celebrity Big Freak is
• if (winner1) cout ltlt Bez ltlt endl
• else if (winner2) cout ltlt Brigitte ltlt
  endl
• else if (winner3) cout ltlt Kenzie ltlt
  endl
• else cout ltlt Does anyone what this rubbish?
  ltlt endl
• return EXIT_SUCCESS

43
Switch Statements

• Switch statements look like this
• switch (expression)
• value_1 statements_1 break
• value_2 statements_2 break
• ...
• value_n statements_n break
• default

44
5. Loops

• The syntax of the For loop in C is identical
  to Java
• for (initialisation condition increment)
• statements
• For example
• int x
• for(x1 xlt100 x)
• cout ltlt Loop Number ltlt x ltlt endl

45
5. Special Cases

• Loops with no bodies, such as a time delay
• for (time0 time lt10000 time)
• You can have as many control variables as you
  want in loops. The following is fine
• for (x0, y0 xylt10 x, y)
• Infinite Loops
• for ( )
• cout ltlt Reality TV, no more, please ltlt
  endl

46
The While Loop

• An example while loop looks like this
• include ltcstdiogt
• int main()
• char ch
• while (ch ! Q)
• ch getchar()
• getchar() reads a character from the standard
  input (usually the keyboard).
• To use it you will need to add include ltcstdiogt
  to the top of your programs.

47
The Do-while Loop

• The do-while loop repeatedly executes a block of
  code indicated by statements as long as the
  conditional expression cond_expr is true.
• do
• someBigBoringCalculation
• while (cond_expr)

48
Continue Break

• The continue statement is used to force program
  execution to the bottom of the loop, skipping any
  statements that come after it, but to continue
  doing the loop on the next itteration.
• The break statement is used to halt execution of
  a loop immediately prior to the loops normal
  test condition being met.

49
Continue Break

• The exit() statement causes the whole program to
  terminate. Much like System.exit(int x) in Java.
  The number passed to the function is returned to
  the OS.
• if(ch Q)
• exit(0)

50
Closing Remarks

• A lot is obviously similar to Java so far. This
  will not remain the case!
• C is way too big to teach in 20-ish lectures.
  You will be required to do plenty of
  self-learning and practicing outside of lectures
  and labs to keep up.
• C is hard work initially, but the most valuable
  language you can learn.
• It is essential not to fall behind! This course
  builds on previous material quite rapidly.
• Lots and Lots of help and resources available to
  you Use Them!

51
Thats all for now

• Next Lecture
• What makes up a C program?
• gcc/g tutorial how to compile and run your
  C programs
• Simple IO Stream usage
• Basic keyboard IO
• Basic file IO