1

Introduction to Computers and Programming

Essential feature of a computer is the separation of operations and data.

2

Hardware Leibnizt 17th Century (adding machine) Babbage 1835 Turing 1936 Post war: ENIAC 30 tons (needed external wiring)

and EDSAC (first stored program) UK – based on Von Neumann Design

Now similar design but speed in MIPS and BIBS rather than 6 – 10!

The physical components Accept input, Display output. Store information. Perform arithmetic and logical operations Control sequence of system

3

The physical components

INPUTINPUT OUTPUTOUTPUT

Memory (RAM)Memory (RAM)Secondary Storage, Hard disk, Secondary Storage, Hard disk,

Floppy, Zip, CDFloppy, Zip, CD

Arithmetic and

logic unit (ALU)

ControlControl

Central Processing Unit (CPU)Central Processing Unit (CPU)

4

The Computer’s Core:CPU and Memory

A collection of switches and relays

Transforms information

User provides input

Computer follows instructions

Returns output to user

Each type understands specific instructions,

Opcodes, (IBM or Mac)

Communicates with the other parts of the

computer.

5

RAM (Random Access Memory)

RAM most common type of primary storage

RAM can store programs and data temporarily

RAM has memory locations with unique addresses

Computers can quickly retrieve from RAM

RAM is volatile memory it is temporary and

constantly changing. Power off — RAM is cleared,

whether you saved it or not!, Save to secondary

storage.

6

Addresses

*

01010011

01000011

01001111

01001111

01001111

01001111

01100111

Imagine a stackof letter boxes.

Each box has a unique address.

Each box has can contain some information (a byte).Each byte has 8 bits which can be a 0 or 1.

0000

0001

3000

3001

3002

64000

: :

: :

63999

Low

High

Memory Memory Address

: :

7

Computer Software

The programs Systems Applications

Like English, programs written in a programming language have their own syntax.Unlike English there are no irregular verbs and exceptions to be learnt

8

Programming Languages

Over 200 languages Language depends upon task Assembly, COBOL, Logo, C++, Pascal, FORTRAN, BASIC.

9

Programming languages (Cont)

Machine languages 11000000 000000000001 000000000010

Add contents of memory location 1 to contents of memory location 2

Horrid to write programs!

Assembly ADD 1 2

Needs an assembler to translate to machine language

Opcode

10

Programming Languages (cont)

Levels of Computer Languages:Low (long way from English) machine language, assembly

High (Closer to English) COBOL, Pascal, FORTRAN, Logo, Basic

Mid-level? C, C++

11

Programming Languages (cont)

Procedural languages focus on tasks. Breaks programs down into sub-procedures. Pascal, Fortran.

Object-Oriented languages (OOP) focus on data, looks at data and operations that are performed on the data. Java, Smalltalk

Special Languages (very high) Prolog, Lisp

12

However

C ++, COBOL, FORTRAN, Pascal, BASIC, Prolog etc.

Computer Can’t Understand English! OR

Computer Understand Machine language.

13

Translation/Interpretation

Translation to Machine Language Interpreter Compiler/linker Assembler

14

Compilation Creating and executable file with C++

source source codecode

compiler -h-files used

object codeobject code linked to libraries

.exe file.exe file

15

Developing/Constructing Programs

16

Problem Solution and Software Development

Phase I: Analysis, Design and Development.Phase II: DocumentationPhase III: Maintenance

17

A Close Look at Phase I

1. Analyse/Solve the problem2. Develop/Design a solution

produce an algorithm3. Code the solution4. Test/Verify the program

18

A Close Look at Phase I

Problem analysis and Solution finding Need a process of solving a problem and

then getting the solution onto a computer.

Initially YOU need to know how to solve a problem in English, before you can get a computer to tackle the problem.The problem is that computers do not understand English.You need to get the solution into a form the computer understands.

19

Problem Solving: generalized problem-solving

approach 1. Understand the problem

1. Roughly sketch out 2. Identify inputs/outputs unknowns,

assumptions.3. Notation: sketch out ideas for variable

names and types.4. Sketch out any equations/relations that

you know or that might be useful.2. Devise a plan

1. Write the plan down!2. Check the plan

3. Implement the Plan1. Check the implementation

4. Examine Solution

20

1. Understand The Problem Draw a figure. What is the data, Try to introduce suitable

variables. What sort of variables should they be?

What is the unknown? What is known? Are there any conditions that need satisfying?

e.g. A grading program will have different grades according to exam scores.

Are the conditions sufficient to determine the unknown? Or is it insufficient? Or redundant? Or contradictory? If not, what do you need to determine the unknown?

Can you write the conditions down?

21

Output of Step 1

One or more pages of rough work, nothing formalGood idea of problem requirementsGood idea of inputs, outputs, constants, conditions, assumptions.

22

2. Devise a Plan Find the connection between the data and

the unknown. You might need to consider separate problems if

you can’t find an intermediate connection. You should eventually come up with a plan of the solution.

Have you seen the problem before? Have you seen the same problem in a

slightly different form? Do you know a related problem? Do you know a theorem that could be

useful? Pythagoras?

23

2. Devise a Plan Continued look at the unknown! And try to think of

a familiar problem having the same or a similar unknown. Is there a problem related to yours and solved before. Can you use it? Can you use its method? Should you introduce some other element in order to make its use possible?

Can you restate the problem? If you cannot solve the proposed

problem, try to solve some related problem first. Can you solve a simplified form with particular conditions.

24

2. Devise a Plan Continued Can you imagine a more accessible

related problem? A more general problem? A more special problem? E.g. If you need to count the number of

words in a file. Solve the sub-problem of counting the number of words on a line first.

Can you solve a part of the problem? Keep only some of the conditions

25

2. Devise a plan continued

Can you derive something useful from the data? Can you think of other data appropriate for determining the unknown? Can you change the unknown or the data, or both if necessary, so that the new unknown and the new data are nearer to each other?

E.g. Change from one coordinate system to another,

Did you use all the data? Did you use all the conditions?

26

Devise a plan continued

Is there a different way of solving the problem. Can you use this to check your solution? is it better?

27

Output of Step 2 Top Down Design

A formal written design.State inputs, outputs

Write steps to process input unambiguously using a semi formal notation (PDL, Flowchart or structure diagram? Can you translate each step of the plan into C++

easily? No … Go back and refine

Verification/testing procedures documented (A test table).

28

3. Coding the Solution

Check code for each step Incrementally. Can you see clearly that the step is correct? Can you prove that it is correct? How would you prove it is correct? i.e. what are the tests you would use to prove your plan?

29

4. Examining the solution

Check the result? Use tests identified in step 2.

Can you use the solution, or the method, for some other problem?

30

So find a solution, write it down in English. Write it down more formally in Pseudo-code

(PDL), or as a structure diagram or a flow chart.

Start your programming environment and convert your pseudo-code to C++

Tell the computer to convert the C++ to machine language (compile)

Tell the computer to load the machine language into memory and execute (Run).

Summary

31

AlgorithmsAn algorithm is simply the technical word for your solution/Plan.It is the step by step sequence of instructions to complete a task it will consist of: Sequences Selection Iteration Invocation

32

Example of Top Down DesignMaking Cups of Coffee

Problem: Make 10 cups of coffee

Initial (Top) PlanMake 10 cups of coffee

Refinement 1Repeat 10 times

Make a cup of CoffeeEnd repeat

33

Example of Top Down DesignMaking Cups of Coffee

Refinement 2Repeat 10 times

Put coffee in CupPut boiling water in Cup

End repeat

34

Example of Top Down DesignMaking Cups of Coffee

Refinement 3Repeat these tasks 10 times

1. Get mug out of cupboard

1.End Repeat2.Get Coffee out of cupboard3.Fill Kettle4.Put Kettle on to boil5.Repeat 10 times

1. Put Coffee in cup2. If Kettle boiled put water in cup3. If wanted Add milk4. If wanted Add sugar

6.End repeat

35

Another Example

Linear SearchProblem:

Find the largest number in a list of numbers.

36

Design Example Linear Search PDLcall the 1st number largestcall the 2nd number current

1 while we are not finished2 if current > largest4 label current as largest5 call next number in the list current6 repeat the while7 output the largest

37

Linear Search Flowchart

largest = first NoCurrent = Second No

Largest = CurrentCurrent > Largest?

Current = Next NoAny more numbers?

Display largest

No

No

Yes

Yes

Start

Stop

38

Phase II Documentation

Improve readabilityYou rememberOthers understandEnables easy maintenance

39

What is documentation

Your formal design paperwork. Should be detailed enough for any

programmer to implement

Comments (annotations) actually written into the code.

40

Phase III Maintenance

Correction of problems after deliveryAdd featuresAdapt to changing needs. E.g. Y2K problem Needs good documentation!

41

What we are aiming for is Structured Programming

AdvantagesNot one giant step, but breaks in to smaller and smaller chunks.Programmer concentrates on details Easy to do in teamsEasy to keep track of developmentCreates more reliable and robust programs.Makes more possible reuse and extensibility.

42

Structured Programming

Errors isolatedDesign written in code Improves reliabilityMinimizes risk of FailureFaster developmentFull documentation Maintainability

43

Writing Down Solution

Designs

FlowchartsPseudo-codeStructure Diagrams

44

•Logical steps

•Written in English

•Language independent

•Labels

•Indenting for logical structures

1. begin game 1.1 display instructions 1.2 pick a number between 1 and 1002. repeat turn until number is guessed or seven turns are completed 2.1 input guess from user 2.2 respond to guess 3. end repeat 4. end game 4.1 display end message

Pseudo-code/ PDL

45

Logical steps representedby standard symbols

display instructionsdisplay instructions

get numberget number

is numberis numbereven?even?

YesYes NoNo

continucontinuee

Flowcharts

46

Structure Diagrams

Inventory Control Program

Enter data Do Calculations

Display report

1 2 3

47

Summary

No Magic BulletAdopt good practice (structured programming)Apply Three Phases Phase I – analyse, develop algorithm,

code test Phase II – Document Phase III - Maintain