CIS05 Comparative Languages Introduction

1
CIS05 Comparative LanguagesIntroduction

• Marc Conrad
• D104a (Park Square Building)
• Marc.Conrad_at_luton.ac.uk
• Outline
• Week 1-6 (MC) C/C, Java, C, other object
  oriented languages as Eiffel, Cecil, ...
• Week 7-12 (Jie Zhang) Other (not necessarily
  object oriented) languages

2
Other information

• Further reading Internet Library.
• Practicals are in the Linux-Lab.
• Marking
• 1st assignment (week 7) 20
• 2nd assignment (week 11) 40
• Exam 40

3
Today

• General introduction into programming languages -
  overview.
• History of C.
• Comparative Languages in Cambridge.
• Example of a C program.
• Structures in C.

4
A history of programming languages - the early
days

• 1957 Fortran. (owned by IBM). Still used for
  scientific computing, current version Fortran 90.
• 1958 ALGOL. Developed as a non-proprietary
  version of Fortran. Not widely used in practice
  but a reference language for many research
  papers.
• 1967 Simula 67. Introduced Classes and
  Inheritance therefore the first Object Oriented
  Programming language.
• 1980 Smalltalk. Develops further Object Oriented
  Concepts

http//www.cs.iastate.edu/leavens/ComS541Fall97/h
w-pages/history/ http//en.wikipedia.org/wiki/Lis
t_of_programming_languages
5
A history of programming languages C and C

• 1972 C. Developed as the implementation language
  of the UNIX operating system. Allows system
  independent low level programming.
• 1979 Bjarne Stroustrup designs C with classes
  which becomes later (1983) C.
• 1989 ANSI C is published - a standardised version
  of C.
• 1989 work on an ISO standard on C begins.
• 1997 ISO C is published.

Bjarne Stroustrup http//www.research.att.com/bs
/
6
A history of programming languages (recent).

• 1991 Python A high level interpreted,
  interactive, object oriented scripting language.
  http//www.python.org
• 1995 Java An object oriented language originally
  designed for video recorders. Now used in many
  application areas. http//java.sun.com
• 1997 PHP 3.0 A general purpose language designed
  for web applications. http//www.php.net
• 2000 C A Java like language for Microsofts .NET
  framework. http//msdn.microsoft.com/vcsharp/

7
Categorisation of Computer Programming Languages

• Classification according to levels of
  abstraction
• Machine code, assembler, high level languages
• Classification according to generations of
  programming languages
• 1GL, 2GL, 3GL, 4GL, 5GL
• Classification according to application area
• General Purpose, Research, AI, Games, ...
• Classification according to paradigm
• Object oriented, procedural, declarative,
  imperative,

8
The programming language C

• Many syntax elements used in a variety of
  programming languages (C, Java, C, javascript,
  PHP, ) today.
• Main application area today System software.
• Especially Linux, Unix
• Compromise between assembly code and
  compatibility.
• Lots of legacy code.
• Overview
• http//en.wikipedia.org/wiki/C_programming_langua
  ge

9
History of C
http//cm.bell-labs.com/cm/cs/who/dmr/chist.html

• before 1960 CPL (Combined Programming Language)
  developed in Cambridge and London.
• 1966 Martin Richards designed BCPL, a simpler
  version of CPL.
• 1969-70 Ken Thompson created B, a simple form of
  BCPL
• 1971-1973 Dennis Ritchie develops C from B by
  adding types. DRs Homepage http//www.cs.bell-l
  abs.com/who/dmr/
• 1978 Kernighan and Ritchie established a de facto
  standard by writing a book on C
• 1989 Ansi C becomes the C standard.

10
The really early history of CBCPL still alive

• Martin Richards Homepage
• http//www.cl.cam.ac.uk/users/mr/index.html
• BCPL uses a virtual machine approach
• http//en.wikipedia.org/wiki/BCPL
• Different in C (direct compilation)
• But similar strategy as in Java!
• A BCPL distribution
• http//www.cl.cam.ac.uk/users/mr/BCPL.html
• MRs lecture comparative languages (Cambridge,
  2003) http//www.cl.cam.ac.uk/Teaching/2003/CompP
  rogLangs/

11
BCPL OCODE (virtual machines)

• From Martin Richards The BCPL Cintcode System
  Users Guide (draft), August 2001,
  http//www.cl.cam.ac.uk/users/mr/index.html

12
Design principles in C

• Pragmatic
• close to the machine
• Efficient
• Use libraries for all system relevant tasks (I/O,
  memory management, )
• Preprocessor (include, define, )

13
Example A C program

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• Output

14
Example A C programThe entry point (main)

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• The entry point of each C program is the main()
  function.
• It does not need to have arguments (cf. Java)
• The return value of main() must be int and will
  be passed back to the operating system.

15
Example A C programBlocks and Statements

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• Curly brackets , are used to structure the
  code.
• Code inside a pair of and is called a block.
• Semicolons are used to separate statements.
• This is still the basis of a number of modern
  programming languages.

16
Example A C programLibraries Header files

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• The include statement is processed by the C
  preprocessor.
• Its meaning is simple Copy the contents of the
  designated file (here stdio.h) in this place
  before compilation.
• The consequence is that we can use other
  functions written by somebody else.
• These header files provide declarations of
  functions that are implemented in libraries.
• stdio.h refers to the header file of the standard
  I/O library.

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Example A C programprintf, sprintf, I/O

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• printf and sprintf are implemented in the
  standard I/O library.

18
Example A C programCompilation

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• So, the compilation of a C program consists of
  three steps
• Run the preprocessor.
• Locally compile the resulting file.
• Link the compiled file together with the
  libraries.

19
Example A C programComments

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• / and / indicate the start and end of a
  comment.
• The // syntax for comments existed in BCPL and
  has been reintroduced in C and Java.

20
Example A C programFunctions, Procedures

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• A C function. The function has no return value
  (void), so it is in fact a procedure.
• The argument of the function is a pointer to a
  character.

21
Example A C programArrays and Pointer

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• An array in C is identified with a pointer.
• So name contains a memory address, and the
  following 10 memory cells are reserved by the
  system for the lifetime of the variable name.
• This allows a very efficient handling of arrays.
• On the other hand it is nearly impossible to
  check for boundaries or memory integrity.

22
Example A C programMemory management (there
isnt any)

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• sprintf writes the contents of the string
  constant Hi Folks! in the memory locations
  following the memory address where name points
  to.
• It does not know if there is enough memory
  reserved, or if the memory location is valid.

23
Example A C programStrings (arrays of
characters)

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• Hi Folks! is stored as H, i, , F,
  o, l, k, s, !, \0where the last
  character (\0) indicates the end of a string.
• If the \0 were missing sprintf would copy
  character after character without stopping (and
  messing up the contents of the memory cells after
  name).

24
Example A C programPointer, Strings - Problems

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• Similarly fiveReverse will print the contents
  of the next five memory cells where str points
  to, independent if this makes sense or not.
• It is not checked if str has been properly
  initialised.

25
Example A C programComplicated Statements

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• This code is equivalent to
• while(i ! 0)
• i i - 1
• i i - 1
• The C while(i--) code is closer to machine
  language
• Branch if zero
• Decrement register
• Today this is largely irrelevant because
  compilers are better in optimising code!

Todays philosophy Produce human readable code!
26
Example A C programPointer arithmetic

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• Pointer arithmetic
• An integer can be added to a pointer value,
• str i means a pointer to a memory cell i places
  away.
• A star stands for the contents of this memory
  cell.

27
Example A C programFormatting Output

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• The first argument of the printf function is a
  format string
• d print an integer
• c print a character
• Also x, e, f, g, s, ,
• See http//www.die.net/doc/linux/man/man3/printf.
  3.html
• Escape sequences for special characters
• \n print a new line (Also \b, \a, \, )

28
Example A C programC and Java (Syntax)

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• Compare with Java
• Some elements are familiar (main, , , void,
  int, char,
• Functions are similar as Java methods.
• There are no classes.
• Arrays are similar declared, but internally they
  are represented differently.
• C libraries contain functions. What does a Java
  package provide?
• C has pointer variables. Has Java something
  similar?
• C has an include statement. How is this related
  to a Java import statement?

29
Example A C programQuestions

• include ltstdio.hgt
• / This function prints the first five
• characters in reverse order /
• void fiveReverse(char str)
• int i5
• while( i-- )
• printf("d c\n", i, (stri) )
• int main()
• char name10
• sprintf(name, "Hi Folks!")
• fiveReverse(name)
• return 0

• What happens when
• you replace 5 by 20?
• replace 5 by 1?
• replace 10 by 3?
• write char name instead of char name3?
• simply write Hi as input instead of Hi
  Folks!?
• Or write Hello World!?

30
Structures a first glimpse of Object
Orientation in C

• A structure groups variables of different types
  together.
• The typedef keyword defines a new data type
  (here Person).
• We say A person has the attributes yearOfBirth
  and lastName20.
• Or The state of a Person is defined by its year
  of Birth and the last name.

• include ltstdio.hgt
• typedef struct
• int yearOfBirth
• char lastName20
• Person
• int main()
• Person fabian
• int thisYear 2004
• fabian.yearOfBirth 1998
• sprintf(fabian.lastName, "Conrad")
• printf("Fabian s is d years old.\n",
• fabian.lastName,
• thisYear - fabian.yearOfBirth )
• return 0

31
Structures a first glimpse of Object
Orientation in C

• This new data type Person can be used in the same
  way as a primitive data type (as int, char, ).
• A variable of type Person is declared.
• The attributes are accessed using a dot (.)
  between the name of the variable and the name of
  the attribute.

• include ltstdio.hgt
• typedef struct
• int yearOfBirth
• char lastName20
• Person
• int main()
• Person fabian
• int thisYear 2004
• fabian.yearOfBirth 1998
• sprintf(fabian.lastName, "Conrad")
• printf("Fabian s is d years old.\n",
• fabian.lastName,
• thisYear - fabian.yearOfBirth )
• return 0

32
Structures a first glimpse of Object
Orientation in C

• In this example
• Person is a very simple form of a class.
• fabian is a very simple form of an object.
• Here, the class Person and the object fabian have
  only state but they do not have behaviour.

• include ltstdio.hgt
• typedef struct
• int yearOfBirth
• char lastName20
• Person
• int main()
• Person fabian
• int thisYear 2004
• fabian.yearOfBirth 1998
• sprintf(fabian.lastName, "Conrad")
• printf("Fabian s is d years old.\n",
• fabian.lastName,
• thisYear - fabian.yearOfBirth )
• return 0

Object Orientation State Behaviour