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Programming Languages

Low-level Languages

High-level LanguagesAdvantages & Disadvantages

TranslatorsTrends in Programming Languages

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Introductionuprogram

a series of instructions make a computer

works

can be written in a variety of programminglanguages

uprogramming lang. - later generations:

fewer instructions

provide a more sophisticated

programmer/computer interaction

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Fourthgeneration

languages

(4GLs)

Fourthgeneration

languages

(4GLs)

Assembler

Assembler

Business

COBOL (1959)

Business

COBOL (1959)

Machine

Machine

Multipurpose

BASIC (1965)Pascal (1968)

Multipurpose

BASIC (1965)Pascal (1968)

Scientific

FORTRAN (1955)

Scientific

FORTRAN (1955)

Procedural languages

High-level

languages

are

problem

oriented

Low-level

languagesare

machine

oriented

4th

gen.

3rd

gen.

2nd

gen.

1st

gen.

More

sophistication

in programmer/

computerinteraction

The hierarchy of programming languages

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Low-level Languages

u

Machine language a programming language that is interpreted &

executed directly by the computer

uAssembly language

a symbolic language with an instruction set thatis basically one-to-one with the machine

language

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Machine language (ML)

ueach computer can only understand

programs that are written in its own ML

u is provided by the computer manufacturer

u translation is needed when executingprograms written in Pascal or BASIC

uwritten at the most basic level of computeroperation

coded as a series of 0s and 1s, e.g., 10111010

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u

Disadvantages: very difficult to write, because:

binary system - not user friendly to human

it requires excellent memorising power

programmer has to keep track of storage

locations of data & instruction

ASSEMBLY LANGUAGE

Machine language (ML)

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Assembly language

u

also provided by the manufactureruone instruction for each computer operation

u

instruction codes are represented bymnemonics (a set of letters)

u the code must be assembled into machine

language for execution

assembly language

[refer to Fig 13.2]

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u

Disadvantages: (similar to that of ML) machine dependent

the program is usually long

hard to learn & slow to write

HIGH LEVEL LANGUAGES

Assembly language

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High-level Languages

u

made programming much more convenientuwritten using common names & words

more like human languagesuproblem-oriented languages

designed to solve specific problems

ue.g., FORTRAN, COBOL, BASIC, Pascal

& C language

[refer to Fig 13.4 - 13.8]

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Advantages of

High-level Languages

u

easier to write, to read & to modify written in English-like format

uprograms - faster & shorter to code

one statement for several computer operations

umore portable, i.e., can be executed by

different computers

machine independent

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u

take up less storage spaceurun faster

u

useful for writing system programs e.g., operating systems (require fast & efficient

use of CPU)

usometimes an operation can only be

performed in a low-level language

Advantages of

Low-level Languages

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Translators

u

programs must be translated into machinecodes before execution

Source

program

Source

program TranslatorTranslator Object

program

Object

programExecution

A simplified translation process

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Translators - 3 typesSource programSource program TranslatorTranslator Object programObject program

ExecutionExecution

assembly

language

programs

assemblylanguage

programs

high-level

language

programs

high-level

language

programs

machine

codes

machine

codes

assemblerassembler

compilercompiler

interpreterinterpreter

The functions of the three types of translators

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Similarities between

compilers & interpreters

uboth translate high-level languages tomachine codes

uboth direct errors in the programs & printerror messages

uboth work out where to store the object

program & its data in the memory

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Compilers Interpreters

Translation of

source program

the whole program

before execution

one line at a time

when it is run

Freqrency of

translation

each line is translated

once

has to be translated

every time it is

executed - slower

Object program can be saved for

future exeutionwithout the source

program

no object program is

generated, so, sourceprogram must be

present for execution

Differences between

compilers & interpreters

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Trends in

Programming Languages

u

fewer instructionsumore user-friendly

u

towards using 4GLs non-procedural language

users only have to state what needs doing, but

not how to do it

designed for users with minimal programming

knowledge & training

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uLogic programming (e.g., Prolog)

5th-generation computer language

declarative language

expert systems & artificial intelligence app.uObject-oriented techniques

e.g., Borland C++

uVisual development environments

e.g., Microsoft Visual Basic

Trends in

Programming Languages