Lecture-2-Programming-Languages-Concepts.pdf

Introduction of Programming Languages Programming Languages Concepts  What is a programming language?  Why are there so many programming languages?  What are the types of programming languages?  Does the world need new languages? What is a programming language?  A programming...

Introduction of Programming Languages Programming Languages Concepts  What is a programming language?  Why are there so many programming languages?  What are the types of programming languages?  Does the world need new languages? What is a programming language?  A programming language is a set of rules that provides a way of telling a computer what operations to perform.  A programming language is a set of rules for communicating an algorithm  It provides a linguistic framework for describing computations What is a programming language?  A PROGRAMMING LANGUAGE is a notational system for describing computation in a machine-readable and human-readable form.  A PROGRAMMING LANGUAGE is a tool for developing executable models for a class of problem domains. What is a programming language?  English is a natural language. It has words, symbols and grammatical rules.  A programming language also has words, symbols and rules of grammar.  The grammatical rules are called SYNTAX.  Each programming language has a different set of syntax rules. Why are there so many programming languages?  Why does some people speak French?  Programming languages have evolved over time as better ways have been developed to design them. ◦ First programming languages were developed in the 1950s ◦ Since then thousands of languages have been developed  Different programming languages are designed for different types of programs. Levels of Programming Languages High-level program Low-level program Executable Machine code  LOW LEVEL LANGUAGES Machine Language :: instructions are written in binary code in it. Only language that computer can execute directly. Assembly Language :: instructions r written using symbolic names for machine operation {READ,ADD,STORE} & operands. Program is then converted into machine language using ASSEMBLER software. HIGH LEVEL LANGUAGE OFFER English like keywords, constructs for sequence, selection & looping and use of variables & constants. Its programs r converted into machine language using compiler or interpreter What Are the Types of Programming Languages  First Generation Languages  Second Generation Languages  Third Generation Languages  Fourth Generation Languages  Fifth Generation Languages First Generation Languages  Machine language  Operation code – such as addition or subtraction.  Operands – that identify the data to be processed.  Machine language is machine dependent as it is the only language the computer can understand.  Very efficient code but very difficult to write. Second Generation Languages  Assembly languages  Symbolic operation codes replaced binary operation codes.  Assembly language programs needed to be “assembled” for execution by the computer. Each assembly language instruction is translated into one machine language instruction.  Very efficient code and easier to write. Third Generation Languages  Closer to English but included simple mathematical notation.  Programs written in source code which must be translated into machine language programs called object code.  The translation of source code to object code is accomplished by a machine language system program called a compiler.  Alternative to compilation is interpretation which is accomplished by a system program called an interpreter.  Common third generation languages  FORTRAN  COBOL  C and C++  Visual Basic Fourth Generation Languages  A high level language (4GL) that requires fewer instructions to accomplish a task than a third generation language.  Used with databases  Query languages  Report generators  Forms designers  Application generators Fifth Generation Languages  Declarative languages  Functional(?): Lisp, Scheme, SML  Also called applicative  Everything is a function  Logic: Prolog  Based on mathematical logic  Rule- or Constraint-based Beyond Fifth Generation Languages  Though no clear definition at present, natural language programs generally can be interpreted and executed by the computer with no other action by the user than stating their question.  Limited capabilities at present. Language Family Tree The principal paradigms  Imperative Programming (C) - assumes that the computer can maintain through environments of variables any changes in a computation process.  Object-Oriented Programming (C++) - in which real-world objects are each viewed as seperate entities having their own state which is modified only by built in procedures, called methods.  Logic/Declarative Programming (Prolog) - takes a declarative approach to problem-solving. Various logical assertions about a situation are made, establishing all known facts. Then queries are made.  Functional/Applicative Programming (Lisp) - views all subprograms as functions in the mathematical sense-informally, they take in arguments and return a single solution. Programming Languages  Two broad groups  Traditional programming languages  Sequences of instructions  First, second and some third generation languages  Object-oriented languages  Objects are created rather than sequences of instructions  Some third generation, and fourth and fifth generation languages Traditional Programming Languages  FORTRAN  FORmula TRANslation.  Developed at IBM in the mid-1950s.  Designed for scientific and mathematical applications by scientists and engineers.  COBOL  COmmon Business Oriented Language.  Developed in 1959.  Designed to be common to many different computers.  Typically used for business applications. Traditional Programming Languages  BASIC  Beginner’s All-purpose Symbolic Instruction Code.  Developed at Dartmouth College in mid 1960s.  Developed as a simple language for students to write programs with which they could interact through terminals.  C  Developed by Bell Laboratories in the early 1970s.  Provides control and efficiency of assembly language while having third generation language features.  Often used for system programs.  UNIX is written in C. Object – Oriented Programming Languages  Simula  First object-oriented language  Developed by Ole Johan Dahl in the 1960s.  Smalltalk  First purely object-oriented language.  Developed by Xerox in mid-1970s.  Still in use on some computers.  C++  It is C language with additional features.  Widely used for developing system and application software.  Graphical user interfaces can be developed easily with visual programming tools. Object – Oriented Programming Languages  JAVA  An object-oriented language similar to C++ that eliminates lots of C++’s problematic features  Allows a web page developer to create programs for applications, called applets that can be used through a browser.  Objective of JAVA developers is that it be machine, platform and operating system independent. Special Programming Languages  SCRIPTING LANGUAGES  JavaScript and VBScript  Php and ASP  Perl and Python  COMMAND LANGUAGES  sh, csh, bash  TEXT PROCESSING LANGUAGES  LaTex, PostScript  HTML  HyperText Markup Language.  Used on the Internet and the World Wide Web (WWW).  Web page developer puts brief codes called tags in the page to indicate how the page should be formatted. Special Programming Languages  XML  Extensible Markup Language.  A language for defining other languages. A language is a language is a language  Programming languages are languages  When it comes to mechanics of the task, learning to speak and use a programming language is in many ways like learning to speak a human language  In both kind of languages you have to learn new vocabulary, syntax and semantics (new words, sentence structure and meaning)  And both kind of language require considerable practice to make perfect. But there is a difference!  Computer languages lack ambiguity and vagueness.  In English sentences such as I saw the man with a telescope (Who had the telescope?) or Take a pinch of salt (How much is a pinch?).  In a programming language a sentence either means one thing or it means nothing. Criteria in a good language design  Writability: The quality of a language that enables a programmer to use it to express a computation clearly, correctly, concisely, and quickly.  Readability: The quality of a language that enables a programmer to understand and comprehend the nature of a computation easily and accurately.  Orthogonality: The quality of a language that features provided have as few restrictions as possible and be combinable in any meaningful way.  Reliability: The quality of a language that assures a program will not behave in unexpected or disastrous ways during execution.  Maintainability: The quality of a language that eases errors can be found and corrected and new features added. Criteria (Continued)  Generality: The quality of a language that avoids special cases in the availability or use of constructs and by combining closely related constructs into a single more general one.  Uniformity: The quality of a language that similar features should look similar and behave similar.  Extensibility: The quality of a language that provides some general mechanism for the user to add new constructs to a language.  Standardability: The quality of a language that allows programs written to be transported from one computer to another without significant change in language structure.  Implementability: The quality of a language that provides a translator or interpreter can be written. This can address to complexity of the language definition.