PROGRAMMING LANGUAGES

Low-level LanguagesHigh-level Languages

Advantages & DisadvantagesTranslators

Trends in Programming Languages

Computer Languages

Used to instruct the computers to work for us Machine languages

Machine code (binary) Assembly languages

Mnemonics (symbolic instruction code) High-level Languages

Like human languages (pseudo code)

Low-level Languages

Machine language a programming language that is

interpreted & executed directly by the computer

Assembly language a symbolic language with an instruction

set that is basically one-to-one with the machine language

Machine language (ML)

each computer can only understand programs that are written in its own ML

is provided by the computer manufacturer

translation is needed when executing programs written in Pascal or BASIC

written at the most basic level of computer operation coded as a series of 0’s and 1’s, e.g.,

10111010

Machine Languages Understood and directly executed by CPU Instruction format :

The fields and their widths comprising the machine instruction

operation code operand/operand address

opcode operand

**Some formats may have two or more operand fields

Disadvantages of Machine Languages

Difficult to learn, understand and memorize

Programming is time consuming and easy to make mistakes, difficult to debug

Machine dependent (cannot be used in computers of other type)

Machine programs are very long Machine oriented (not problem oriented)

very difficult to write, because: binary system - not ‘user friendly’ to huma

n it requires excellent memorizing power programmer has to keep track of storage loca

tions of data & instruction ASSEMBLY LANGUAGE

Disadv. Of Machine language (ML)

Programs & Progr. Lang.

program a series of instructions make a computer

‘works’ can be written in a variety of programming

languages programming lang. - later generations:

fewer instructions provide a more sophisticated

programmer/computer interaction

The hierarchy of programming languages

Fourth generationlanguages

(4GLs)

Fourth generationlanguages

(4GLs)

AssemblerAssembler

BusinessCOBOL (1959)

BusinessCOBOL (1959)

MachineMachine

MultipurposeBASIC (1965)Pascal (1968)

MultipurposeBASIC (1965)Pascal (1968)

ScientificFORTRAN (1955)

ScientificFORTRAN (1955)

Procedural languages

High-levellanguages

areproblemoriented

Low-levellanguages

aremachineoriented

4thgen.

3rdgen.

2ndgen.

1stgen.

More sophisticationin programmer/computerinteraction

Assembly language

also provided by the manufacturer one instruction for each computer operatio

n instruction codes are represented by mnemonics (symbolic instr. code)

the code must be assembled into machine language for execution

One-one correspondence with ML

Disadvantages: (similar to that of ML) machine dependent the program is usually long hard to learn & slow to write

HIGH LEVEL LANGUAGES

Assembly language

High-level Languages

made programming much more convenient

written using common names & words,more like human languages

problem-oriented languages designed to solve specific problems

e.g., FORTRAN, COBOL, BASIC, Pascal & C++(object-oriented)

Advantages of High-level Languages

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

programs - faster & shorter to code one statement for several computer operations

more portable, i.e., can be executed by different computers (with slight modifications) machine independent

take up less storage space run faster useful for writing system programs

e.g. operating systems (require fast & efficient use of CPU)

sometimes an operation can only be performed in a low-level language (can access the hardware directly)

Adv. of Low-level Languages

Translators

Programs (except ML) must be translated into machine codes before execution

Sourceprogram

Sourceprogram TranslatorTranslator Object

program

Objectprogram

Execution

A simplified translation process

Translators - 3 types

Source programSource program TranslatorTranslator Object programObject program

ExecutionExecution

assemblylanguageprograms

assemblylanguageprograms

high-levellanguageprograms

high-levellanguageprograms

machinecodes

machinecodes

assemblerassembler

compilercompiler

interpreterinterpreter

The functions of the three types of translators

Compilers Interpreters

Translation of source program

the whole program before execution

one line at a time when it is run

Frequency of translation

each line is translated once

has to be translated every time it is executed - slower

Object program can be saved for future execution without the source program

no object program is generated, so, source program and interpreter must be present for execution

Compilers Interpreters

Translation of source program

the whole program before execution

one line at a time when it is run

Frequency of translation

each line is translated once

has to be translated every time it is executed - slower

Object program can be saved for future execution without the source program

no object program is generated, so, source program and interpreter must be present for execution

Differences betweencompilers &

interpreters

Trends in Programming

Languages fewer instructions (more high-level) more user-friendly towards using 4GLs

non-procedural language users only have to state what needs to

be done, but not how to do it designed for users with minimal

programming knowledge & training

Logic programming (e.g., Prolog) 5th-generation computer language declarative language expert systems & artificial intelligence applicati

on Object-oriented techniques

e.g., Borland C++ Visual development environments

e.g., Microsoft Visual Basic

Trends in Programming

Languages