This document provides an overview of programming languages and programming methodologies. It discusses what programming languages and computer programs are, provides a brief history of programming languages, and outlines attributes of good languages. It then covers different programming methodologies including unstructured programming, procedural programming, and object-oriented programming. Object-oriented programming is described as keeping large software projects manageable by decomposing problems into understandable modules that can be developed incrementally and combined through interfaces. The main features of object-oriented languages that support this approach are also listed.

1. Programming Languages
Lecture 1
Naveen Kumar

2. 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

3. 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
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Computer program is a specification of a computation.

4. What is Programming Language
4
ComputerProgram
Programming
Language
Output
use
giveswriteUser
executes
Problem
takes

5. 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

6. 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

7. Programming Methodology
Kind of approach to solve different problems
 How should programs be designed?
 How should programs be structured?

8. 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

9. Kinds of Programming Methodology
 Unstructured programming
 Procedural/Process oriented programming
– Modular programming
 Object-oriented programming

10. Unstructured Programming
 Direct code (step)
Ex: Assembly Language
Adv.
 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

11. 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
Small
functions

12. 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

13. Object-Oriented Programming
Keep large software projects manageable by
human programmers
 Bottom-up approach (user oriented)
 Objects are building block

14. 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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15. 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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16. Why OOP?
Modularization
 Decompose problem into smaller
subproblems that can be solved separately.
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17. Why OOP?
Abstraction -- Understandability
 Individual modules are understandable by
human readers.
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18. Why OOP?
 Encapsulation -- Information Hiding
 Hide complexity from the user of a software.
Protect low-level functionality.
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19. Why OOP?
 Composability -- Structured Design
 Interfaces allow to freely combine modules to
produce new systems.
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20. Why OOP?
 Hierarchy
 Incremental development from small and
simple to more complex modules.
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Complexity
increases

21. Why OOP?
 Continuity
 Changes and maintenance in only a few
modules does not affect the architecture.
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22. 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