Lect 1. introduction to programming languages

 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?

 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

PS — Introduction

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.

 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 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.

High-level program class Triangle {
class Triangle {
...
...
float surface()
float surface()
return b*h/2;
return b*h/2;
}
}
Low-level program LOAD r1,b
LOAD r1,b
LOAD r2,h
LOAD r2,h
MUL r1,r2
MUL r1,r2
DIV r1,#2
DIV r1,#2
RET
RET
Executable Machine code 0001001001000101
0001001001000101
0010010011101100
0010010011101100
10101101001...
10101101001...

 First Generation Languages
 Second Generation Languages
 Third Generation Languages
 Fourth Generation Languages
 Fifth 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.

 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.

 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

 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

 Declarative languages
 Functional(?): Lisp, Scheme, SML

◦ Also called applicative
◦ Everything is a function
 Logic: Prolog
◦ Based on mathematical logic
◦ Rule- or Constraint-based

 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.

 Imperative Programming (C)
 Object-Oriented Programming (C++)

 Logic/Declarative Programming (Prolog)

 Functional/Applicative Programming (Lisp)

 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

 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.

 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.

 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.

 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.

 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.

 XML
◦ Extensible Markup Language.
◦ A language for defining other languages.

 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.

 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

 Formerly: Run-time performance
◦ (Computers were more expensive than programmers)
 Now: Life cycle (human) cost is more important
◦ Ease of designing, coding
◦ Debugging
◦ Maintenance
◦ Reusability
 FADS

 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.

 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.

Lect 1. introduction to programming languages

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Lect 1. introduction to programming languages