Introduction to programming by ewghwehws

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									Introduction to
programming

                  Carl Smith
             National Certificate
              Year 2 – Unit 4
Unit objectives
   Apply simple analysis and design
    techniques to the software development
    process.
   Develop basic high-level code using an
    appropriate procedural programming
    language.
   Use suitable testing methods to ascertain
    the correctness of a working piece of code.
   Produce appropriate documentation for a
    given program application.
Programming languages
  Pascal is one language among
  others such as:-
  C, C++, VB, JAVA, COBOL, ADA,
  BASIC, Fortran…
  Each has strengths and weaknesses
  for various tasks, for example COBOL
  is ideal for data processing
Why Pascal?
   Experts consider Pascal is ideal for
    students studying computer science
    courses because:-
     It forces structure, very “elegant”
     “Easy” to learn

     Very powerful
Blaise Pascal, 1623-1662
  The Pascal language was named after
  the 17th century mathematician, Blaise
  Pascal who invented a calculating
  machine called “the Pascaline” which
  could add and subtract and worked with
  eight rotating gears. Tax clerks of the
  era viewed it as a threat to their jobs
  and it was never adopted!
  Program development
           Analyse
                             Good program
                             development is
                             performed in 4 main
                             steps…
Document             Write




           Test              (which match the unit
                             objectives - strangely…!)
Program development…
 In fact there are 6 steps:-
 1. Analyse the problem


                         }
 2. Develop algorithm
 3. Write code               Step 2
 4. Run the program
 5. Test the results
 6. Document the program
Analysis Phase
   Analysis is not a trivial task
   Before you can code you need to know
    exactly what you are to do
   You need a clear and precise statement of
    what is to be done
   You need to understand what data is
    available and what is to be assumed
   You need to know what output is desired
    and the form it should take
Development (Develop/Write/Run)
Phase
 Develop an Algorithm, which is:-
  “A finite sequence of effective
  statements that when applied to a
  problem, will solve it”
 Write code for the program when
  the algorithm solves the problem
 (Compile) and Run the program:-
    At this point you may discover typing or
     logic errors!...
    Testing phase
   Test that the results are correct and in the
    form you like
   Prove that your program produces the
    correct solution in all cases:-
    e.g. with arithmetic operations this may mean
      checking with a calculator or even pencil and
      paper!
   After this phase you may need to go back
    to the development or even analysis phases
    so the whole process becomes a “cycle”
Documentation phase
   It is very important to fully document a
    working program
   He writer knows how the program works
    (hopefully!) but if others are to modify it
    they must know the logic used
   Documentation can also be included in
    the development phase as remarks within
    the pseudo and actual code
Developing Algorithms
   Algorithms for solving problems can be
    developed by:-
       Stating the problem
       Dividing the problem into major sub-tasks
       Dividing each sub-task into smaller tasks
       Repeating the process until each task is easily
        solved
   This is known as “Top Down” design
Software “Life-Cycle”
 Analysis
 Design
 Coding
 Testing/Verification
 Maintenance
 Obsolescence
What is programming?
 Giving the computer a logical set of
  instructions to perform a specific
  task
 That is, taking the design algorithm
  and converting it to code that the
  computer “understands”
Compiled v Interpreted
   Languages either run “Interpreted” that is
    each line of code is interpreted into pseudo
    machine code (binary) at run time
   Or Compiled, which is the whole program is
    compiled, prior to running it, into pseudo
    machine code
   Interpreted languages tend to be slower in
    execution but are easier to develop and
    debug because the interpreter is available to
    pin point errors at run time
   Pascal is a compiled language but the
    compiler is part of the “Turbo Pascal”
    development environment
Turbo Pascal 7
 MSDOS based environment
 Therefore 8.3 filenames
 Support for the mouse but mainly
  used via the keyboard
 Runs in a window or full screen
  under Windows 95/98 or 2000
Turbo Pascal v7 – Main
Turbo Pascal v7 - Editor
Output name program
    Program Components
   Remarks – “Self documenting code”
   Program Structure
   Declarations – Variables/Constants & Data
    Types
   Input, Output & Formatting
   Arrays


    Decisions – “IF”
    Iteration - Looping}    “Nesting”

   Arithmetic and regular expressions
   Commands, Procedures and Functions :–
    In Built and User Defined
Pascal - Program Structure
Program <name>;




                               }
                               Program Name
Uses Crt; - output to screen
Const
<list of constants>                     Declaration
Var                                     section
<list of variables>
<list of subprograms>
BEGIN

END.
                               }    Executable
                                    section
Summary
   We covered:-
    National Certificate Unit 4 objectives
    The software development cycle
    The software life cycle
    Intro to Turbo Pascal 7
    Program Elements and structure

    Any Questions?

								
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