Programming Languages and Software Engineering

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Programming Languages and Software Engineering
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Topics

• discuss some of the underlying commonalities and
  differences among programming languages
• explain what there is to learn about software
  engineering beyond programming

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Learn Programming in Ten Years(Peter Norvig)

• it takes time/practice/experience to learn to
  become a good programmer
• you can learn syntax in one semester (or from a
  book), but...
• need to built up a repertoire of problems you
  have previously solved, so when you face a new
  problem, you can draw upon your prior experience,
  youve seen it before design patterns

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• Norvigs suggestions
• Get interested in programming, and do some
  because it is fun..
• Program. The best kind of learning is learning by
  doing.
• Talk with other programmers read other programs.
  
• Work on projects with other programmers.
• Work on projects after other programmers.
• Learn at least a half dozen programming
  languages.
• Remember that there is a "computer" in "computer
  science". Understand how it works.
• Get involved in a language standardization
  effort.

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• In CSCE 121, we teach C because it is widely
  used for large industrial applications.
• Many additional computational concepts are
  introduced in this course, such as how compilers
  work, object-oriented design, etc.
• There are many other languages - do you need to
  learn them all?

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• Assembler
• Fortran, Pascal, COBOL, Basic
• Ada, Modula, PL/1, Simula, MatLAB
• Haskell, LISP, Scheme
• C, C, C, Objective-C
• Smalltalk, Java, Javascript
• PERL, PHP, TCL, Python, Ruby
• csh, awk, sed
• Prolog a logic-based language for making
  inferences from knowledge bases
• Postscript a stack-based language for printers

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source http//calvinx.com/tag/programming-languag
es/
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Two Interesting Questions

• Why are there such a bewildering array of
  languages?
• historical artifact some languages evolved
  into, or inspired, other languages
• some languages started out as experiments to test
  new ideas or features, like OO and
  message-passing in Smalltalk
• some languages are more suited for certain
  applications, like Fortran for numerical
  computing, or PERL/Python for processing text
  files
• there are special-purpose languages like
  Postscript (or MatLAB, Simula) that are
  custom-designed for certain tasks (printing,
  simulations...)

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Two Interesting Questions

• Isnt C overkill for writing low-level code
  like drivers/controllers/firmware? wouldnt C be
  much more efficient with less overhead?
• this is a common misconception
• by this reasoning, why not use assembler?
• modern C compilers have many optimizations that
  make code fast/competitive
• most importantly, C allows code to be expressed
  in a more comprehensible (generic, factored) way
  that facilitates maintainability and long-term
  use of code over many years
• these issues often outweigh a few extra
  microseconds
• the original programmer might be long gone, and
  someone else has to find and fix a bug

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Programming

• The same algorithm can be implemented in many
  programming languages.

in C
in Python
in Java
import sys if __name____main__ a
int(sys.argv1) b int(sys.argv2) if
altb b,a a,b while bgt0 r ab
a,b b,r print GCD is,a
include ltstdio.hgt void main(int
argc,charargv) int a,b,temp
sscanf(argv1,d,a) sscanf(argv2,d,b)
if (altb) tempa ab btemp while
(bgt0) int rab ab br
printf(GCD is d\n,a)
public class GCD public static void
main(String args) int a,b,temp aInteger.pa
rseInt(args0) bInteger.parseInt(args1)
if (altb) tempa ab btemp while
(bgt0) int rab ab br
System.out.println( "GCD is "a)

• Point 1 Once you understand the general
  principles (which you will learn in CSCE 314),
  you just have to learn the syntactic variations
  in each language
• Point 2 There are some unique language
  differences/features including user-created
  types, polymorphism, list comprehension,
  exceptions, function objects...

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• In CSCE 314, you will learn the structure of
  languages and what unites them, so you can
  eventually learn to program in any of them
• major classes of languages
• imperative/procedural languages
  (block-structured)
• Pascal, Fortran, C, Ada...
• functional languages (expression evaluation)
• Scheme, LISP, Haskell...
• object-oriented (encapsulation, message
  passing)
• Smalltalk, Java, Objective-C, C
• logic-programming
• Prolog
• (of course, some languages blur these
  distinctions)

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• I already showed examples of procedural
  programming
• here is the functional version of factorial and
  GCD written in LISP
• (this is an interactive command line I typed
  into)
• gt(defun fact (n) (if (lt n 1) 1 ( n (fact (- n
  1)))))
• FACT
• gt(fact 10)
• 3628800
• gt(defun gcd (x y)
• (if (lt x y) (gcd y x)
• (if ( y 0) x (gcd y (mod x
  y)))))
• GCD
• gt(gcd 112 40) // running a program is done by
  evaluating an expression
• 8

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• interpreted vs. compiled languages
• interpreters read in lines and execute directly
• compilers
• convert source code to low-level language (.exe,
  assembly language, executable CPU instructions)
• have to learn about regular expressions, parsing,
  syntax and semantics, optimization...
• compare Python and C
• block structure
• think how the body of a for loop or if
  statement is marked in different languages (,
  endfor, change of indentation)
• type systems
• can users define new types and operations on
  them? like structs and classes, example Complex
  s
• object-oriented languages
• classes, inheritance, polymorphism...
• extensions for concurrency, exception-handling,
  real-time applications...

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• Here is an example of an object-oriented
  definition of Rectangles in Java

public class Rectangle int height,width //
interval variables // initializer public
Rectangle(int a,int b) heighta widthb
int area() return heightwidth
static Rectangle BoundingBox( Rectangle
A,Rectangle B) int hmax(A.height,B.height)
int wmax(A.width,B.width) Rectangle Cnew
Rectangle(h,w) return C
public static void main(String args)
Rectangle Pnew Rectangle(3,2) Rectangle
Qnew Rectangle(1,4) Rectangle
RBoundingBox(p,q) System.out.println(
P(3,2) area"P.area()) System.out.println(
Q(1x4) area"Q.area())
System.out.println( R(3x4)
area"R.area())
27 sungt java local/testRectangle p(3,2)
area6 q(1x4) area4 r(3x4) area12
P h3, w2
R h3, w4
Q h1, w4
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Learning Unix (part of CSCE 312/Systems)

• why learn this? is it necessary?
• many command-line development tools
• (compared to IDEs like MS Visual Studio)
• Unix has well-defined concepts and principles
• executables, flags, pipes, streams, sockets...
• multitasking
• many powerful tools for software development
• editors like Emacs
• compilers like g
• make files (for multi-file projects)
• debuggers like gdb
• source-code control like CVS or SVN

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Software Engineering (CSCE 431)

• software engineering usually involves working in
  teams
• requirements gathering/writing specifications
  (with customer)
• UML (Unified Modeling Language)
• diagram out how your modules work and interact
• libraries reuse of code
• e.g. APIs for image processing, network access,
  speech recog...
• large projects have many dependencies
• testing defining test cases as important as
  writing code
• documentation
• explain how things work, why it was designed that
  way, ASSUMPTIONS, alternatives, limitations...
• version control
• issue new number with each change to file, e.g.
  v3.0.12
• critical so you can identify and undo mistakes
• life-cycle models
• waterfall, rapid prototyping, extreme programming
  (partners)...
• metrics for tracking/estimating number of bugs
  over time