Programming Languages

Lecture 1

Naveen Kumar

The Study of Programming Languages

The purpose of language is simply that it must convey meaning (Confucius)

Whatever can be said, can be said clearly (Wittgenstein,1963)

A programming language is a notation for writing programs (Sethi,89)– program is a specification of a computation.2

What is a programming language?

A language that is intended for the expression of computer programs and

that is capable of expressing any computer program

3Computer program is a specification of a computation.

What is Programming Language

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ComputerProgram

Programming Language

Output

use

giveswriteUser

executes

Problem

takes

A short history of programming Languages

Early languages:– Numerically based languages. (FORTRAN:55,ALGOL:58)– Business languages. (COBOL:60)– Artificial intelligence languages. (LISP,Prolog)– Systems languages. (C:70)

1950 : LISP, FORTRAN, COBOL, ALGOL60, BASIC 1970 : Ada, C, Pascal, Prolog 1980 : C++ 1990 : Delphi, Perl 1996 : Java by James Gosling (at SUN Micro Systems)5

Attributes of a good language

Clarity and simplicity– Readability

Naturalness for the application Ease of program verification

– Proof of correctness, test– Simplicity of semantic and syntax

Portability of programs Cost of use

– Program execution– Program translation– Program creation, testing, and use– Program maintenance6

Programming Methodology

Kind of approach to solve different problems

How should programs be designed?

How should programs be structured?

Programming Methodologies Influences

1950s and early 1960s: Simple applications; worry about machine efficiency

Late 1960s: People efficiency became important; readability, better control structures

– structured programming– top-down design

Late 1970s: Process-oriented (Goal or.) to data-oriented (DB or.)

– data abstraction

Middle 1980s: Object-oriented programming– Data abstraction + inheritance + polymorphism

Kinds of Programming Methodology

Unstructured programming Procedural/Process oriented programming

– Modular programming Object-oriented programming

Unstructured Programming

Direct code (step)

Ex: Assembly LanguageAdv. speed (written in assembly)Disadv. No re-usability Statements written many times As code increases, complexity increases

– Hard to manage large programs – Hard to debug

Procedural oriented Programming

Top-down approach Procedure (Function) are building block De-allocation problem (memory leak: memory allocated

but not used) Un- initialized Variables (rand value assigned)Ex: Calculator → scientific

→ non-scientific → float→ int → add.

→ subs.→ mult.→ div.

Ex: C - language

Smallfunctions

Procedural oriented Programming

Adv:– Re-usability– Easy to debug

Disadv:– Concentrate on what we want to do, not on who will use it– Data does not have a owner (sharing) – All functions are global– No data security

Ex: let there are three functions a(),b() and c(). Data d is used by a() and b() but how to restrict from c() [data will be either global or local]

– No data integrity [Stack:{push,pop},Queue:{enque, deque}] How to distinguish which fun associated with which data

structure

Object-Oriented Programming

Keep large software projects manageable by human programmers

Bottom-up approach (user oriented) Objects are building block

An Example

Everything in OOP is grouped as self sustainable "objects".

let’s take your “hand” as an example. – Your body has two objects of type hand, named left hand and

right hand. Their main functions are controlled/ managed by a set of electrical signals sent through your shoulders

– So the shoulder is an interface which your body uses to interact with your hands.

– The hand is being re-used to create the left hand and the right hand by slightly changing the properties of it.

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Another Example

Ex: college (Student, Faculty, Admin)

Student (take course, write exam, view indv. result)Faculty (set paper, prepare result, view results)Admin (student admission, staff/faculty selection)

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Why OOP?

Modularization Decompose problem into smaller

subproblems that can be solved separately.

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Why OOP?

Abstraction -- Understandability

Individual modules are understandable by human readers.

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Why OOP?

Encapsulation -- Information Hiding

Hide complexity from the user of a software. Protect low-level functionality.

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Why OOP?

Composability -- Structured Design

Interfaces allow to freely combine modules to produce new systems.

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Why OOP?

Hierarchy

Incremental development from small and simple to more complex modules.

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Complexityincreases

Why OOP?

Continuity

Changes and maintenance in only a few modules does not affect the architecture.

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Main OOP Language Features

Classes: Modularization, structure. Inheritance / extends: Hierarchy of modules,

incremental development. Public / Protected / Private: Encapsulation. Interfaces / Abstract Classes: Composability. Polymorphism / virtual: Hierarchy of modules,

incremental development. Templates: Type independent abstract data

types. 22