CS101 Introduction to Computing

LectureProgramming Languages

Today’s Lecture

• To understand the role of programming languages in computing

• To understand the differences among low- & high-level, interpreted & compiled, and structured & object-oriented programming languages

Programming?

The process of telling the computer what to do

Also known as coding

Types of Programs?

Batch ProgramsThese are typically started from a shell (or automatically via a scheduler) and tend to follow a pattern of:

– Initialize internal data – Read input data – Process that data – Print or store results

Key feature: No user interaction with the computer while the program is running

Examples?

Event-Driven ProgramsExamples? GUIs, microwave, camera

The system sends events to the program and the program responds to these as they arrive.

Events can include things a user does - like clicking the mouse - or things that the system itself does - like updating the clock.

These programs generally work as follows:

– Initialize the internal data – Wait for events to arrive– Identify an incoming event and react accordingly

ProgrammingLanguage?

A vocabulary and set of grammatical rules for instructing a computer to perform specific tasks

All programs consists of:

1. Sequence of instructions

2. Conditionals

3. Loops

These may contain:– Data– Input/output (print, etc)– Operations (add, divide, etc)

Examples of ProgrammingLanguages?

Machine LanguageAssembly Language (1956-63)LISP (1956)Fortran (1957)COBOL (1959)PL/1(1964)BASIC (1964)Pascal (1970)Smalltalk (1972)C (1972)

Ada(1983) C++ (1983-85) QBasic (1986)Perl (1987)VisualBasic (1991)PowerBuilderJava (1995)JavaScriptC# (2001)

Is HTML a programming

language?

Types ofProgramming Languages?

High level Programming Languages

Low Level Programming Languages

High-level programming languages, while simple compared to human languages, are more complex than the languages the uP actually understands, called machine languages

Each different type of uP has its own unique machine language

Lying betweenmachine languages&high-level languagesare languages calledassembly languages

Assembly languages are similar to machine languages, but are easier to program in as they allow a programmer to substitute names for numbers

Machine languages consist of numbers only

4th-generation languages

High-level languages

Assembly languages

Machine languages

walks!

Regardless of what language you use, you eventually need to convert your program into a language that the computer can understand

Two ways for doing that:compile the program or

interpret the program

Interpreter is a program that executes instructions written in a high-level language

An interpreter translates high-level instructions into an intermediate form, which it then executes

In contrast, a compiler translates high-level instructions directly into machine language

Compiled programs generally run faster than interpreted programs

The advantage of an interpreter, however, is that it does not need to go through the compilation stage during which the whole of the high-level code is translated into machine instructions in one go. This process can be time-consuming if the program is long.

The interpreter can immediately execute high-level programs, without waiting for the completion of the translation process

Interpreters:Immediate response,

butexecute code slowly

Compilers:Takes longer to compile,

butsuper-fast execution

Both interpreters and compilers are available for most high-level languages

However, BASIC and LISP were especially designed to be executed by an interpreter

Why are there so many different programming languages?

What is the difference between

them?

What are the advantages of

particular languages?

The question of which language is best is one that consumes a lot of time and energy among computer professionals

Every language has its strengths and weaknesses

FORTRAN is a particularly good language for processing numerical data, but it does not lend itself very well to large business programs

Pascal is very good for writing well-structured and readable programs, but it is not as flexible as the C programming language

C++ embodies powerful object-oriented features, but it is more complex and difficult to learn as compared with Java

The choice of which language to use can also depend on the:

type of computer the program is to run on,

and the

expertise of the programmer

Can a single language have all the good bits of

other languages?

Do some good features force a language to also

have bad features?

What makes a feature good

or bad?

Is there a perfect

language?

Is there a perfect

language for a particular task?

What changes in the field of computer languages can we expect in the near

future?

Which programming language should you

learn?

Should you learn more than one?

?Programming

SWDevelopment

SWDesignDesignMethodology?

The set of (often flexible) rules and guidelines a team of developers follow to construct reasonably complex SW systems

Object Oriented Design (1)

• OO SW is all about objects: a black box which receives messages & responds with those of its own

• An object has 2 aspects:– Properties, also termed as state, data

• Example: For the bicycle: color, speed, pressure

– Methods, also termed as behaviors, instructions• Example: For the same object: accelerate(), inflate()

• In traditional design, these 2 aspects have been kept apart

Object Oriented Design (2)

• The designer starts with any component (object) of the system; designs it as an independent, self-contained system, and then moves to the design of some other component

• The over-all system is put together by fitting together a collection of these components

• Key feature: Details of the design of the component are kept independent of the over-all system– Benefit: It can be easily re-used in other systems:

design once; use multiple times

Structured Design (1)

• Also called top-down design

• The designer starts by first conceiving a skeleton high-level design of the system, and then starts defining features of that over-all design in an ever-increasing detail

• Making small changes in the functionality of the systems sometimes leads to a major re-design exercise

Structured Design (2)

• Structured design emphasizes separating a program's data from its functionality

• Separating data from functionality typically leads to SW that is difficult to maintain & understand - especially for large SW systems

Object-Oriented Languages

• Programming languages specifically designed to make it easy to implement object-oriented designs

• Examples: Smalltalk, C++, Java

Reading Material

Programming Languages

http://www.wikipedia.com/wiki/Programming_language

Goals of Today’s Lecture were …

• To understand the role of programming languages in computing

• To understand the differences among low- & high-level, interpreted & compiled, and structured & object-oriented programming languages

Focus of the Next Lecture:The SW Development Process

• Development process of reasonably complex SW systems does not consist of “coding” only

• We will become familiar with the various phases of the process that developers follow to develop SW systems of reasonable complexity