BIL 106E Introduction to Programming in F General Course Related Information

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BIL 106E Introduction to Programming in
FGeneral Course Related Information Lecture
Notes

• Version 1.1
• Last Update Sep 9, 2005

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General Information

• BIL106E is an internet-assisted course.
• The official course website is at
  www.be.itu.edu.tr Lisans Dersleri BIL106E
• It is the students responsibility to check this
  website to find out about announcements, homework
  and midterm solutions and lecture notes.
• There may be newer versions of lecture notes or
  any other file that you see at the course
  website, due to either a correction, or the
  inclusion of a better explanation, or a new
  example.

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General Information

• AGAIN, it is the students responsibility to
  check if there are newer versions of the files
  posted at the course website.
• Note that all the files posted at the course
  website will have a version number in their file
  names, such as BIL_106_INTRO_SLIDE_v1.1.ppt or
  BIL_106_INTRO_SLIDE_v1.1.zip. (Note that if a
  file is compressed with WinZip its extension
  changes to .zip. In order to uncompress it, you
  need to download WinZip or WinRar from
  www.download.com and install it in your computer.
  This download is free of charge.)
• If version 1.1 is what you have downloaded and
  the next time you visit the course website, you
  notice that there is a file with name
  BIL_106_INTRO_SLIDE_v1.2.ppt, or .zip, you should
  download version 1.2 and immediately delete
  version 1.1.
• This is known as VERSION CONTROL. It is your
  foremost responsibility to do version control in
  any computing project including keeping track of
  lecture notes.

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General Information (contd)

• There are 3 sections and 3 instructors for this
  course.
• The two midterms and the final exam will be
  common to all 3 sections.
• Homeworks and quizzes will be different for each
  section.
• The letter grade will be based on a single bell
  curve instead of 3.

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General Information (cont)

• Breakdown of the letter grade
• Final Exam 40
• 2 Midterms Each 20
• Labwork, Homeworks, Quizzes and In-class bonus
  points 20
• The third item above will be determined
  separately by each instructor.
• The result will then be standardized using
  3 separate curves from the 3 sections.
• The standardized grade will then count as
  20 towards your letter grade.
• Each instructor is free to decide whether
  or not to give in-class bonus points.
• Since the results will be standardized at
  the end, this will not be a setback for any
• section.

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General Information (cont)

• Useful Websites
• http//www.foldoc.org
• (Free OnLine Dictionary of Computing)
• http//www.merriamwebster.com
• (English Dictionary Thesaurus)
• http//www.zargan.com
• (Turkish-English English-Turkish Dictionary)

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What is FORTRAN?

• Fortran "FORmula TRANslation" is the oldest
  language still in general use, dating back to
  1957, the year the Space Age began. It excels at
  the first task computers were called on for
  number-crunching.
• This is the language that literally put a man on
  the moon, and some of the features it developed
  in the process of that project (and other less
  glamorous ones) have yet to be duplicated in
  other, more "modern" languages.

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What is F?

• F is a subset of FORTRAN.
• The F compiler was written by Walt Brainerd, one
  of the authors of your textbook.

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Why teach a subset of FORTRAN and not a
full-fledged version of FORTRAN?

• F has all the necessary components of FORTRAN to
  write efficient computer programs.
• F is easier to learn and to teach.

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What is the most well-known version of FORTRAN?

• FORTRAN77, or F77, for short.

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What is the major difference between FORTRAN77
and FORTRAN90?

• F90 can be used for parallel programming whereas
  F77 cannot.
• Note that F is also amenable to parallel
  computing, but this is beyond the scope of BIL106.

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What is the latest full-fledged version of
FORTRAN?

• FORTRAN2003.

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Can we use pointers in F just like in C?

• Yes, you can.
• This is within the scope of BIL106 starting from
  this semester.

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Is Object-Oriented Programming possible in
FORTRAN just like in C?

• Yes, there is a new book by Ed AKIN that explains
  how to do that using FORTRAN95, but this is
  beyond the scope of BIL106.

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What is a computer?

• Hardware
• Processor
• Memory
• I/O units (Input/Output Units)
• How does it work?
• Executes very simple instructions.
• Executes them incredibly fast.
• Must be programmed it is the software, i.e., the
  programs, that characterize what a computer
  actually does.

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Simplified architecture of a computer
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What is a computer program?

• The computer program characterizes what a
  computer actually does.
• A program (independently of the language in which
  it is written) is constituted by two fundamental
  parts
• A representation of the information (data)
  relative to the domain of interest.
• A description of how to manipulate the
  representation in such a way as to realize the
  desired functionality operations.
• To write a program both aspects have to be
  addressed.

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A recipe that combines operations is an
Algorithm

• We need a recipe (just like the ones in a
  cookbook) that combines certain operations in
  order to solve a specific problem.
• Example given a person name, find the
  corresponding telephone number in a telephone
  registry.
• To delegate to a computer the solution of a
  problem, it is necessary to find an algorithm
  that solves the problem.

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Algorithms

• An algorithm is a recipe through which we obtain
  the solution of a problem. In other words, a
  sequence of instructions that, when executed in
  sequence, allow one to calculate the solution of
  the problem starting from the information
  provided as input.
• An algorithm is characterized by
• non ambiguity the instructions must be
  interpretable in a unique way by whom is
  executing them
• executability it must be possible to execute
  each instruction (in a finite amount of time)
  given the available resources
• finiteness the execution of the algorithm must
  terminate in a finite amount of time for each
  possible set of input data

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Example of an Algorithm for the Previously Given
Problem

• Scan the person names, one after the other as
  they appear in the registry until you have found
  the requested one then return the associated
  telephone number.
• Are there other algorithms to solve a given
  problem?
• Yes!

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Exercise

• Write an algorithm for a stupid robot so that it
  can light
• gas stove (ocak).
• Here is how you could start writing the
  algorithm
• Find a box of matches.
• Stand in front of the gas stove.
• Turn the dial of the stove so that gas starts to
  come out.
• Take out a match from the box.
• Try to light the match.
• If not lit go to step 4.
• If lit
• You may want to modify this algorithm a little
  bit. )

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What next?

• Once we have found/developed an algorithm, we
  have to code it in the selected programming
  language.

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The edit-compile-verify cycle
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Is reaching the end in the previous flowchart
enough?

• No, because you may have programmed an incorrect
  algorithm that produced a result without giving a
  compiler error or a run-time error.
• For instance you might compute the age of the
  universe using a rough algorithm and find 42 as
  the result.
• Obviously, the result is incorrect due to a
  logical error, which can either be an
  implementation error, or an algorithmic error,
  which is much worse than a simple implementation
  error.

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Logical Errors are either Implementation Errors,
or Algorithmic Errors, or both

• How does one discover logical errors in a
  computer program?
• You need to test your program using test
  problems. These test problems should start from
  very simple problems and go towards more
  difficult problems. You can never be 100 sure
  that a program does not have any logical errors
  until you, or the user discovers it while using
  the program. The more testing you do, the more
  likely that your code does not have any logical
  errors in it.
• If you discover a logical error, you have to
  write a correct implemention of the algorithm
  that you used.
• If this does not work either, you have to find a
  better algorithm and implement that algorithm
  without any implementation errors.