Introduction to programming languages

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Introduction toprogramming languages
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Objectives

• Concepts of programming
• Programming languages
• Development of computer programs

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Why computer programs ?

• Problems
• Arranging the text of a letter
• Collecting and maintaining data about customers
• Calculating the best investment portfolio
• Making a photo with your mobile phone
• Synchronising the components of car engine
• Computer programs aim to solve such problems
  related to electronically stored and processed
  data

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Solving problems

• Problem description
• Data collections
• Problem analysis (including data analysis)
• Designing a solution
• Implementing the solution

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Algorithms

• Algorithm systematic processing of actual or
  virtual data
• Specification of input and output data
• Specification of methods of data processing
• E.g. Euclids greatest common divisor algorithm
• a, b two positive numbers which is their gcd ?
• x a, y b
• If x gt y then n x, d y otherwise n y, d x
• n q d r, x d, y r
• If y 0 then gcd x

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Early computers

• Binary data entry punch-cards
• Machine language e.g. MOV A,B LLR etc.
• Difficult to program easy to make errors

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Constants and variables

• Constant a fixed value, e.g. 5
• Constant a fixed value with a name, e.g. a5
• Variable x a place holder for a value (e.g.
  number, text)
• assignation of a value to a variable the
  contents of the variable with a given name takes
  a certain specified value
• Makes sense x x 1
• x 5, x x1, now the value of x is 6
• Other variables s Hello!, y (2,
  apples, table)

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Data types

• Data is stored in variables with names
• Variable name type contents
• Type determines what kind of contents the
  variable may have e.g. integer, floating point
  real, string, combination of other data types
• E.g.
• int x, x 5 is allowed, x 5.1 is not allowed
• string s, s hello kids is allowed, s 3 is
  not allowed
• Type definition for combined types
• addr record (int nr, string st, string ct,
  string pc)
• addr a, a (5, Hyde, York, YO2 4RH)

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Operators

• Operators , -, concatenate, lt
• a53, sconcatenate(hot, dog), alt5
• Each type has a range of operators that can be
  applied to variables of that type
• Operator overload some operators may apply in
  different ways to data of different types
• In case of subtypes, e.g. real and integer,
  additional operators may apply to the subtype
  e.g. integer division

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Early programming languages

• Fortran, Cobol
• Better than machine code
• Introduce flow control

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Flow control 1 (conditions)

• If-then-else
• Branching depending on condition
• If ltconditiongt then ltTblockgt else ltFblockgt
• E.g.
• If x5 then a2 else a1
• If (signal, left) then (turn, left) else (turn,
  right)

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Flow control 2 (loops)

• for fixed length cycling
• for ltinit statementgt, ltincrement statementgt,
  ltcondition statementgt, ltexecution statementgt
• E.g.
• for i1,a1, ii1, ilt100, do aai
• while, repeat variable length cycling
• while ltcondition statementgt, ltexecution
  statementgt
• repeat lt execution statementgt, ltcondition
  statementgt
• E.g.
• while ilt100, do aai, ii1
• repeat aai, ii1, until i100

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Structured programming

• Structured programming was introduced in the late
  60s early 70s
• Pascal, C
• Flow control is packaged into procedures, data
  are separated between program structures ? better
  understanding, better design, better programs
  with fewer errors

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Procedures and functions

• Procedures blocks of programs containing flow
  control structures with a set of specified input
  data and a set of specified output data
• Functions similar to procedures, but generates a
  single output data (i.e. it is like a function)
• Procedures are called with a set of actual values
  of their formal input variables and a set of
  variables specified for their formal output
  variables
• E.g.
• procedure Draw (int x,y,z,w)
• procedure Prediction (int x,y,z var int a,b)
• int function Length (string s)
• Length(hello)
• Draw(10,10,50,50)

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Recurrent procedures

• Recurrent procedure procedure that calls itself
• Data separation
• E.g.
• Procedure Gcd (int a,b var int g)
• int x,y,r,q,n,d
• xa yb
• if xgty then nx dy else ny dx
• qn div d rn qd
• xd yr
• if y0 then gx else Gcd(x,y,g)
• end

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Object oriented programming

• Object oriented programming emerges in the 70s
  and becomes mainstream programming paradigm in
  the late-80s early 90s
• Aims
• Better description of real world problems
• Better software design
• Increased reliability of large software systems
• Smalltalk, Delphi, C, C, Java

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Classes and objects 1

• Class encapsulation of data and data
  manipulation, such that interference with outside
  is the minimal necessary
• Class attributes and methods some visible from
  the outside, most visible only inside
• E.g.
• Class Square
• int llx,lly,dx,color
• Create
• Destroy
• Draw
• FillDraw
• Square S , S.Create an object is an instance of
  a class

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Classes and objects 2

• Classes can be defined as derivatives of other
  classes inheritance
• Derived classes inherit attributes and methods
  from the parent class and may add further
  attributes and methods to these or may change the
  definition of some inherited
• E.g. Class Rectangle (Square)
• int dy (new attribute)
• (int llx,lly,dx,color inherited)
• Draw (redefined)
• FillDraw (redefined)
• Rotate (new method)
• (Create, Destroy inherited)

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Flow control with exceptions

• Objects are instances of classes and many objects
  exist simultaneously ? concurrent execution of
  objects
• Objects interact by sending messages i.e.
  invoking methods of them, which are visible from
  the outside
• Flow control try catch throw
• Exception incorrect execution because of some
  reason
• E.g.
• try
• R.Draw
• return(OK)
• catch (exception e)
• throw GraphicsExceptionFault
• return(Error)

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Functional programming

• Everything is written as a function, the program
  is a combination of functions
• LISP
• Applied in AI (Artificial Intelligence)

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Declarative programming

• Instructions are not necessarily specified
  directly
• What is wanted is declared, but how to get it is
  not specified
• Prolog logic programming used in AI
• SQL database language
• Declarative programming is closer to natural
  language than imperative programming (describing
  how to do things e.g. C, C, Java), but it may
  imply much longer execution time

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Compilation vs. interpretation

• Compilation the program is translated into a
  sequence of machine codes that can be executed
  directly by the processor the whole program is
  translated (compiled) at once, when it is
  finished, the compiled program is executed ?
  compilers
• Interpretation the program is interpreted by
  taking instructions/declarations one-by-one, each
  interpretation leads to a brief machine code
  translation that is executed, then the next
  instruction/declaration is interpreted the
  program is translated (interpreted) as it is
  executed, and at any time only a small part is
  translated into machine code ? interpretors
• Compilers usually generate faster running
  programs, while interpretors leave more space for
  interactive use of programs

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Interpreted or compiled?

• BASIC
• C/C
• Java
• R
• Matlab
• Perl

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Reusable software

• Developing software takes long time it is
  desirable to re-use existing software to solve
  partial problems of new problems
• Re-use is facilitated by documentation
  description of what is written in the program and
  why
• Early programming languages did not support very
  much re-use
• Object oriented programming languages provide
  very much support for re-use

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Component-based programming

• Component-based programming is the current major
  trend in software development
• New software is built by combining existing
  components in novel ways relies very much on
  re-use of existing software
• E.g. classes or objects can be purchased or used
  as service providers, most of the software does
  not have to written from scratch for example
  handling of a printer or reading standard file
  formats (like XML)

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Software development

• Problem analysis
• Data analysis
• Design
• Development and integration
• Prototype
• Testing
• Use and maintenance

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Software development problem analysis

• What is the problem that needs the software
  solution
• E.g.
• Management of data bases in a uniform manner
• Visualisation of complex scientific data
• Identification of users
• Collection of information and data about user
  needs and requirements
• Analysis of collected information and data

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Software development data design

• Collection and analysis of relevant data
• Analysis of data formats needs and requirements
• Design the relevant information flow
• Design data structures supporting the information
  flow
• Design processing of the data

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Software development integration implementation

• Development of software components implementing
  the design
• Acquiring existing components based on design
  requirements, and analysis of features of
  existing components
• Integration of existing components and writing of
  integration software and possible other
  components that cannot be bought-in off-the-shelf

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Software development prototype testing

• Development of a small-scale prototype to test
  functionalities
• Testing of components of the software system
  test scenarios, use cases
• Elimination and correction of faults and errors

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Software development use and maintenance

• Installation and training of users
• Deployment of the software
• Maintenance
• Updates and patches

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Summary

• Algorithms
• History of programming languages machine code
  early languages Fortran, Cobol structured
  programming Pascal, C object oriented
  programming C, C, Java functional
  programming Lisp declarative programming SQL
• Constants, variables, data types
• Flow control structures if-then-else, for,
  while, repeat
• Procedures and functions
• Classes encapsulation, inheritance
• Compilers and Interpreters
• Software development process

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Q A

• Is it true that Java is a declarative language ?
• Is it true that only variables of the same type
  can be compared by comparison operators ?
• Can we use the for flow control mechanism to
  execute the same set of operations for 10 or 20
  times depending on the value of some processed
  data ?
• Is it true that a class is an instance of an
  object ?
• Can we use the try-catch-throw flow control in
  concurrent environments, with many objects
  executed at the same time ?
• Can we develop a prototype of a software before
  meeting the users to collect user requirements ?