Prof. Ken Regis Institute for Computer Engineering

Florida State University

Oktober 2002 Prof. Ken Regis - FIT 1-1 1

Ken Regis

Why learn about programming?

programming teaches you how to solve problems

programming helps you be more precise (doesn’t win you many friends though!)

why did the computer scientist stay in the shower forever?the instructions on the shampoo said “lather, rinse, repeat!”

programming gets you more out of your computer

you may not be programming, butknowing a little bit about Computer Scienceand knowing a little bit about Programmingwill help you work with people who do

ProgramsA program is a set of step-by-step

instructions that directs the computer to do the tasks you want it to do and produce the results you want.

You have already programmed!You wrote complex formulas in Excel

=$D5*EKSP(-LN(2)*E$4/$C5)

You used SQL to talk to databasesSELECT * FROM contacts

WHERE age BETWEEN 18 AND 35;

You programmed in MATLABfunction r = fz(x)global M p w1; X = [cos(x), sin(x); -sin(x), cos(x)]; r1 = M' - p' - X*w1'; r = r1'*r1;

ProgrammingProgramming consists of two steps:

algorithmic design (the architects) coding (the construction workers)

Programming requires: a programming language to express your ideas a set of tools to design, edit, and debug your code either

a compiler to translate your programs to machine code a machine to run the executable code

or an interpreter to translate and execute your program

Programming LanguagesA programming language is a set of rules

that provides a way of telling a computer what operations to perform.

Levels of Programming LanguagesMachine languageAssembly LanguageHigh Level LanguagesFourth Generation Languages (4GL)Fifth Generation Languages (5GL)

Machine Languagesdifferent for each computer processor

0100001101 100000 001101 11000100101 10001 1000001110111001. . .

Assembly Languagesdifferent for each computer processor

main proc paymov ax, dsegmov ax, 0b00hadd ax, dxmov a1, b1mul b1, axmov b1, 04h

High-Level LanguagesHigher Level Languages

Use traditional programming logic where the programming instructions tell the computer what to do and how to perform the required operations.

4GLsUse high-level English-like instructions to

specify what to do, not how to do it .

Types of high level Programming Languages

Procedure-oriented languagesObject-oriented languagesEvent-driven languagesDeclarative languages

Procedure-Oriented LanguagesFORTRANCOBOLPascalCAda

OOED Languages

Object-oriented languagesSmalltalkC++Ada 95JavaC#

Event-driven languagesVisual Basicmost Visual languages

Declarative languages (5GL)Functional(?): Lisp, Scheme, SML

Also called applicativeEverything is a function

Logic: PrologBased on mathematical logicRule- or Constraint-based

Lots more LanguagesThere are many programming languages out

therespecification languages, e.g. Z, UMLdocument languages, e.g. LaTeX, Postscriptcommand languages, e.g. csh, MATLABquery languages, e.g. SQLScripting languages, e.g. Perl, Python,

JavaScript, VBScript, ASP, PHP, …

What determines a “good” languageFormerly: Run-time performance

(Computers were more expensive than programmers)

Now: Life cycle (human) cost is more importantEase of designing, codingDebuggingMaintenanceReusability

FADS

Why so many?Why does some people speak French?Most important: the choice of paradigm, and

therefore language, depends on how humans best think about the problem

Other considerations:efficiencycompatibility with existing codeavailability of tools

What can a program do?A program can only instruct a computer

to:SequenceCalculateStore dataCompare and branchIterate or LoopWrite OutputRead Input

Sequence Control StructuresSequence control structures direct the order

of program instructions.The fact that one instruction follows another

—in sequence—establishes the control and order of operations.

CalculateA program can

instruct a computer to perform mathematical operations.

Add 1 to

Counter

StoreA program will often

instruct a computer to store intermediate results.

Place 1 in

Counter

Compare and Branch

A program can instruct a computer to compare two items and do something based on a match or mismatch which, in turn, redirect the sequence of programming instructions.There are two forms:IF-THENIF-THEN-ELSE

IF-THEN

Test Test condition pcondition p

falsefalse truetrue

EntryEntry

ExitExitTrue True

statement astatement a

IF-THEN-ELSE

falsefalse truetrue

EntryEntry

ExitExit

Test Test condition pcondition p

““true” true” statement astatement a

““false” false” statement astatement a

IterateA program loop is a

form of iteration. A computer can be instructed to repeat instructions under certain conditions.

NoNo

Iteration Control StructuresIteration control structures are looping

mechanisms. Loops repeat an activity until stopped. The

location of the stopping mechanism determines how the loop will work:

Leading decisionsTrailing decisions

Leading DecisionsIf the stop is at the beginning of the iteration,

then the control is called a leading decision.The command DO WHILE performs the

iteration and places the stop at the beginning.

DO WHILE Loop

NoNo

YesYes

EntryEntry

ExitExit

Test Test condition pcondition p

Loop Loop statement astatement a

Trailing DecisionsIf the stop is at the end of the iteration, the

control mechanism is called a trailing decision.

The command DO UNTIL performs the iteration and puts the stop at the end of the loop.

DO UNTIL Loop

Loop Loop statement astatement a

NoNo YesYes

EntryEntry

Test Test condition pcondition p

ExitExit

Programs are Solutionsto ProblemsProgrammers arrive at these solutions by

using one or more of these devices:Logic flowchartsPseudocodeStructured ProgrammingUMLObject Oriented Programming

Logic FlowchartsThese represent the

flow of logic in a program and help programmers “see” program design.

Terminator. Shows the starting and ending points of the program. A terminator has flowlines in only one direction, either in (a stop node) or out (a start node).

Data Input or Output. Allows the user to inputdata and results to be displayed.

Processing. Indicates an operation performed by the computer, such as a variable assignment or mathematical operation.

Decision. The diamond indicates a decision structure. A diamond always has two flowlines out. One flowlineout is labeled the “yes” branch and the other is labeled the “no” branch.

Predefined Process. One statement denotes a group of previously defined statements. For instance, “Calculate m!” indicates that the program executes the necessary commandsto compute m factorial.

Connector. Connectors avoid crossing flowlines, making the flowchart easier to read. Connectors indicate where flowlines are connected. Connectors come in pairs, one witha flowline in and the other with a flowline out.

Off-page connector. Even fairly small programs can have flowcharts that extend severalpages. The off-page connector indicates the continuation of the flowchart on another page. Just like connectors, off-page connectors come in pairs.

Flowline. Flowlines connect the flowchart symbols and show the sequence of operations during the program execution.

Common Flowchart Symbols

Start

sum=0

Input price

sum=sum+price

Moreitems?

vat=sum x 0.25total=sum+vat

Output sum, vat, and total

Stop

No

Yes

PsuedocodeThis device is not visual but is considered a

“first draft” of the actual program.Pseudocode is written in the programmer’s

native language and concentrates on the logic in a program—not the syntax of a programming language.

sum=0While More items do Input price sum=sum+priceEnd Whilevat=sum x 0.25total=sum+vatOutput sum, vat, total

Structured ProgrammingStructured program languages lend

themselves to flowcharts and pseudocode.Structured programming languages work

best where the instructions have been broken up into small, manageable parts.

Object Oriented ProgrammingEverything is an objectA program is a bunch of objects telling

each other what to do by sending messages

Each object has its own memory made up of other objects

Every object has a typeAll objects of a particular type can

receive the same messages(Alan Kay)

The object conceptAn object is an encapsulation of data and

behaviour, modeled after real-world objectsAn object is an instance of an abstract data typeAn abstract data type is implemented via a classAn object has

identity (a unique reference) state (also called characteristics) behaviour

Behaviour is implemented via methods Methods are often implemented using structured

programmingAn objects methods and state are access via dot

notation I.e document.write(“Hello World”)

Analyze the problem

Design the solution algorithm

Design the user interface

Write the code

Test and debug the program

Complete the documentation

Programming and DebuggingWrite code

Syntax Rules of the language

Logic Order of execution of various parts of the program

Programming and DebuggingProgramming Errors

Syntax error Misuse of syntax

e.g., typing fer instead of for

Logic errors Unintended operation of program

e.g., Infinite loop

Programming and DebuggingDebugging

Tracing and resolving errors in a program Coined by Admiral Grace Hopper

Moth short-circuited a relay “bug” in the system

Removed it system “debugged” Not an exact science – more a black art Human against evil machine!

So really, why learn about programming?Programmers make lots of money. Programming really is fun. Programming is very intellectually

rewarding. Programming makes you feel superior to

other people. Programming gives you complete control

over an innocent, vulnerable machine, which will do your evil bidding with a loyalty not even your pet dog can rival.