Introduction to programming

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Introduction to programming

• Carl Smith
• National CertificateYear 2 Unit 4

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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.

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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

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Why Pascal?

• Experts consider Pascal is ideal for students
  studying computer science courses because-
• It forces structure, very elegant
• Easy to learn
• Very powerful

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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!

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Program development

• Good program development is performed in 4 main
  steps(which match the unit objectives -
  strangely!)

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Program development

• In fact there are 6 steps-
• Analyse the problem
• Develop algorithm
• Write code
• Run the program
• Test the results
• Document the program

Step 2
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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

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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!...

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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

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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

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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

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Software Life-Cycle

• Analysis
• Design
• Coding
• Testing/Verification
• Maintenance
• Obsolescence

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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

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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

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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

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Turbo Pascal v7 Main
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Turbo Pascal v7 - Editor
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Output name program
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Program Components

• Remarks Self documenting code
• Program Structure
• Declarations Variables/Constants Data Types
• Input, Output Formatting
• Arrays
• Decisions IF
• Iteration - Looping
• Arithmetic and regular expressions
• Commands, Procedures and Functions In Built
  and User Defined

Nesting
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Pascal - Program Structure

• Program ltnamegt
• Uses Crt - output to screen
• Const
• ltlist of constantsgt
• Var
• ltlist of variablesgt
• ltlist of subprogramsgt
• BEGIN
• END.

Program Name
Declarationsection

Executablesection
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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?