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lect1-introductiontoprogramminglanguages-130130013038-phpapp02.ppt

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

 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.

 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.

 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.

 A variable is a label assigned to a value.
 The symbol = is the assignment operator (and
not the equals symbol!), and it can be
pronounced is assigned
 The symbol + is the concatenation symbol
when dealing with strings (and not the plus
symbol!)

•Variable: A named storage location in memory that holds a
value.
•Syntax: The set of rules that defines the combinations of
symbols that are considered valid in the programming language.
•Operator: A symbol that performs a specific operation on one
or more operands (e.g., +, -, *, /).
•Operand: A value or variable that an operator acts upon.
•Function: A reusable block of code that performs a specific
task.
•Data Type: A classification that specifies the type of data (e.g.,
integer, float, string, list).
•Conditional Statement: A statement that executes different
code blocks based on whether a condition is true or false.

 At the gym. You are the manager of a gym and
you have to register a new person. What
variables would you create? Write three
variables, assign a value to each of them (make
sure they are strings!), and print them out.

 Question: Write a Python program that takes
two numbers as input from the user and
calculates their sum.
1. Prompt the user to enter the first number.
2. Prompt the user to enter the second number.
3. Calculate the sum of the two numbers.
4. Print the result in a formatted message.

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