Tonga Institute of Higher Education IT 141: Information Systems

1
Tonga Institute of Higher EducationIT 141
Information Systems
Lecture 14 Programming
2
Software Engineering

• Computer programming is also known as software
  engineering.
• It covers the entirety of developing software,
  which includes systems analysis and programming.
• It can involve hundreds of people and many months
  or years to finish a really big software project
• Microsoft Word has about 750,000 lines of code.
  The US government only thinks a program is big if
  it is over 1 million lines of code

3
Problem Statement

• So how do we start engineering software?
• Its best to start with defining the things we
  need to do and to know
• A Problem Statement is a list of things that
• Specifies all aspects of the problem
• Clearly specifies all the information we know
• Specifies when the problem is solved
• With this information, we can figure out the
  problems we want to solve and how to solve them

4
Algorithms

• With this information about the problem, we can
  create an algorithm to solve it.
• An algorithm is a series of steps that can be
  written down and coded into a program.
• If the instructions of an algorithm are followed,
  then you will always get the right answer (If the
  algorithm was made correctly)
• Usually, you must be pretty detailed with your
  instructions. Computers are stupid.

5
How to write algorithms

• Structured English This is using regular
  language to write out your algorithm
• Multiply the length by the height to get the area
• Pseudo-Code Mixes programming code and language
  to make something that looks like code, but would
  never compile
• Area length x height
• Flowchart this uses pictures and graphics to
  help you understand the algorithm

6
Flowchart of Algorithm
Start
Input width Input height
multiply
width
height
Output area
7
Coding

• Programs are called sequential order programs,
  because the commands happen in order.
• That is unless, you make them go somewhere else
• Control structures will control the sequence of
  the instructions in the programming.
• Examples if, else, functions, etc
• They will change the flow of a program

8
Control Structures

• Sometimes we will draw pretty pictures to show
  how a control structure works

9
Repetition Controls

• Repetition Controls are ways to make something
  happen many times.
• These are called loops. In programming you may
  use "for" and "while" to make this happen
• Theyll have some condition that either makes
  them continue doing the loop or stop the loop.

10
Debugging And Documentation

• To make sure your program works, you have to do a
  lot of testing.
• The biggest problem is finding errors or "bugs"
  and removing them
• Sometimes testing takes longer than programming

People who write programs with lots of problems
look like this
11
Errors

• There are three types of errors you may get when
  you make a program
• Syntax errors when you dont follow the
  guidelines of the programming language. Maybe you
  forgot semi-colons or spaces
• Run-time errors errors that happen after you
  compile and start running a program. Maybe you
  tried to divide by zero.
• Logic errors when your algorithm and procedures
  dont do what they are supposed to, but the
  program still runs

12
Documentation

• Its a good idea to put comments within your
  programs.
• It makes it easier for people to read, for you to
  remember what you did, and also for other people
  to continue working with your code
• Once you have a program that runs, its also a
  good idea to have documentation that tells people
  how to actually use the program.

13
Programming Languages

• Hundreds of programming languages have been
  invented since computers started
• Some were invented for specific purposes (like
  business or math) and some are general purpose
• A procedural programming language has a series
  of statements that execute one after each other.
• Programs start at the beginning and end at the
  end. They follow a simple flow through the code,
  it is easy to see what is happening (one example,
  BASIC)

14
Programming Languages

• Object oriented languages they try to let
  programs use an object to manipulate data and
  change things.
• An object will be defined by a class. Inside the
  class there will be methods which allow people to
  do things to the object.
• There will also be attributes inside the object
  which describe something about the object. These
  are mostly variables that define data inside the
  object

15
Object-Oriented

• So why do we use object oriented programming?
• It lets many people work on a program at once
  because they can all work on small parts
  themselves
• It lets people use things that others did without
  having to understand them
• It lets things be reused a lot, instead of
  redoing the same thing over and over again

16
Declarative Languages

• Declarative languages let programmers define a
  set of rules and statements about some
  relationship or problem.
• Then inside the compiler, it applies those rules
  to get the answer.
• The programmer does not have to actually write
  out the answer, but instead he just writes the
  rules.
• Then the compiler does the hard work of solving
  the problem.
• One example is SQL

17
Markup and Scripting Languages

• We know that markup languages are not really
  programming languages, because they are simple
  tags inserted into regular text to make it look
  different
• Scripting languages are like most programming
  languages, except they cannot be run without an
  interpreter.
• They are sometimes not as powerful as programming
  languages that can be compiled.

18
Low-Level Languages

• Low-level languages (also called Assembly
  Languages) are used when the programmer wants to
  work directly with hardware. People who write
  compilers and who write operating systems use
  this
• Machine language - the language of 1s and 0s that
  the processor uses to execute the program.
• It cannot really be understood by humans. When
  computers were first invented people had to use
  1s and 0s in order to program
• Assembly language is the direct translation of
  machine language. It has simple commands that
  will change memory or do simple arithmetic.
• It can be understood by people, but not as easily
  as high level languages (languages you need to
  compile in order to change to a low-level
  language)

19
Compilers

• Compilers turn your high-level programming
  language into low level assembly language. Your
  code is called source code
• The low-level code that comes out of a compiler
  is called object code. Sometimes it is ready to
  be run right away, because it is an executable.
  Sometimes it is turned into an intermediate
  language.
• One example of an intermediate language is with
  Java. Java allows you to compile your program
  into byte-code. This byte code can then be run
  on any computer. Javas goal is to eliminate the
  problem that programs written on one system
  cannot work on another.

20
Interpreters

• Interpreters will only compile one instruction at
  a time. It will look at the current instruction,
  turn it into machine language and let it be
  executed. Then the next instruction will be
  changed into machine language.
• It is a little slower than when a compiled
  program runs because each line of code needs to
  be changed into machine language as it is running.

21
Event-Driven

• Some programs run based on something that
  happens. This is the case in graphical
  programming.
• It might wait for a mouse-click, something to
  move, or something entered from the keyboard
• These are called events and if your program
  responds to these, it is called an event-driven
  program

22
Components

• Because of object-oriented programming, you can
  buy or download components (or objects) that will
  do things for you.
• You dont even need to know how they work
• You just plug them into your program and use what
  they do.
• For example, maybe your program needs to make a
  graph, so you can get a graph component.
• This graph component might display a graph for
  you with the data that you give it (data
  independence!)

23
Programming Languages Overview

• Visual Basic and Basic procedural programs that
  can be compiled. Easy to use. Visual Basic very
  easy to use to make graphical programs.
• C procedural programming that gives access to
  hardware, but is still high-level. Smart people
  can use C to make their programs very fast, but
  its hard to learn
• C - like C, but with objects. Many people cant
  understand this idea of objects, so they give up

24
Programming Languages Overview

• COBOL language made in the 1960s for large
  business mainframes. It is procedural, easy to
  understand and has lasted for a long time
• Java high level, object-oriented language that
  is good for internet programs (called applets)
  and can run on any computer without being
  re-compiled
• Pascal high level, procedural language made for
  students to learn with, but nobody can make a
  real program out of it
• SQL the standard, declarative language for
  using databases.

25
Programming Languages Overview

• Perl It is a high-level scripting language that
  lets you programming with objects or treat it
  like a procedural program
• PHP Another high level scripting language that
  is entered right into HTML.
• .NET Languages (C, VB.NET) A new set of
  languages made by Microsoft that extend older
  languages by adding object oriented programming
  and try standardize Windows programming.
• It doesnt require types and lets you mix lots of
  things together. It is also easy to make simple
  programs. No compiling!

26
Summary

• Most of the information in this chapter should be
  familiar with you, after having been exposed to
  programming already
• We went over some new things, like different
  types of languages and different things you can
  do with objects
• We also looked at different programming languages
  and what makes them unique