This document discusses the evolution of programming languages from machine languages (1GL) to natural languages (5GL). It begins by defining a programming language as a formal notation system that describes computation in a readable and machine-readable form. It then categorizes generations of programming languages based on their level of abstraction, from low-level machine codes (1GL) to high-level languages (3GL) to domain-specific languages (DSL). The document provides examples and characteristics of languages from each generation.

1. What is a Programming Language?
PS — Introduction © O. Nierstrasz
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• A formal language for describing computation?
• A “user interface” to a computer?
• Syntax + semantics?
• Compiler, or interpreter, or translator?
• A tool to support a programming paradigm?
A programming language is a notational
system for describing computation in a
machine-readable and human-readable form.
— Louden

2. 2
Figure 9.2 Categories of programming languages

3. Generations of Programming Languages
1GL: machine codes
2GL: symbolic assemblers
3GL: (machine-independent) imperative languages (FORTRAN,
Pascal, C ...)
4GL: domain specific application generators
5GL: AI languages … ( Prolog, OPS5, and Mercury are examples of
fifth-generation languages.)
Each generation is at a higher level of abstraction
PS — Introduction © O. Nierstrasz
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4. CSC141 Introduction to Computer Programming
Machine language (1GL)
• The lowest level of language.
• The language used to program the first-generation
computers.
• The instructions in 1GL are made of binary
numbers, represented by 1s and 0s.
• 1s and 0s correspond to the on and off states of
electrical switches.
• Suitable for the understanding of the machine
but very much difficult to interpret and learn by
the human programmer.

5. Machine Language(contd)
• is not portable
• runs only on specific type of computer
• is made up of binary-coded instructions (strings of 0s
and 1s)
• is the language that can be directly used by the
computer
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6. CSC141 Introduction to Computer Programming
Assembly language (2GL)
• Low-level language that allows a programmer to use
abbreviations or easily remembered words instead of
numbers.
• These Observations are called Mnemonics. These
Mnemonic are Opcode and Operands
For Example: ADD AX, BX
MOV CX, AX
INC CX
Op-code; ADD, MOV, INC
Operands AX, BX,CX

7. CSC141 Introduction to Computer Programming
Assembly language (2GL) (contd)
• Programmer can write instructions faster but it is still not
an easy language to learn.
• Drawback: The language is specific to a particular
processor family and environment. (Machine Dependent
Language)
• Assembler – A program that translates the assembly
language program into machine language.

8. High Level languages (3GL)
• A High-Level Language is an English-like language.
• It is a refinement of a second-generation programming
language.
• It allowed users to write in familiar notation, rather
than numbers or abbreviations.
• Most High-level languages are not Machine Dependent.
• Translator for High-level languages is either a Compiler
or an Interpreter.
• Examples of High-level languages:
―FORTRON
―COBOL
―BASIC
―C and C++
CSC141 Introduction to Computer Programming

9. High Level Languages (contd)
• are portable
• user writes program in language similar to natural
language
• examples -- FORTRAN, COBOL, Pascal,
Ada, Modula-2, C++, Java
• most are standardized by ISO/ANSI to provide an
official description of the language
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10. CSC141 Introduction to Computer Programming
Very-High-Level Languages (4GL)
• 4GLs are much more user-oriented and allow programmers to
develop programs with fewer commands compared with 3GLs.
• Non-Procedural Language; Programmers don’t have to specify all
the programming logic, only tell the computer what they want
done.
• Saves a lot of time.
• 4GLs consist of report generators, query languages, application
generators, and interactive database management system
• For example:
• RPG III (Report Generator)
• SQL (Structured Query Language)
• NOMAD and FOCUS (DBMS)

11. Domain specific languages(DSL)
• Specialized to a particular application domain.
• Contrast to a general-purpose language (GPL), which is broadly
applicable across domains, and lacks specialized features for a
particular domain.
• Wide variety of DSLs, ranging from widely used languages for
common domains.
• Sometimes informally called mini-languages.
• Example: HTML for web pages.

12. CSC141 Introduction to Computer Programming
Natural Languages (5GL)
• Two types
• Ordinary Human Languages; like English.
• Programming language that use human language to give
people a more natural connection with computers.
• 5GLs are designed to make the computer solve a given
problem without the programmer.
• Natural languages are part of the field of study known as
Artificial Intelligence.
• Develop machines to emulate human-like qualities such
as learning, reasoning, communicating, seeing and
hearing.

13. What is Computer Programming?
• It is the process of planning a sequence of steps
(called instructions) for a computer to follow.
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STEP 1
STEP 2
STEP 3
. . .

14. Problem Solving
How do you solve problems?
Understand the problem
Devise a plan
Carry out the plan
Look back
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15. Strategies
Ask questions!
• What do I know about the problem?
• What is the information that I have to process in order the find the
solution?
• What does the solution look like?
• What sort of special cases exist?
• How will I recognize that I have found
the solution?
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16. Strategies
Ask questions! Never reinvent the wheel!
Similar problems come up again and again in different guises
A good programmer recognizes a task or subtask that has been
solved before and plugs in the solution
Can you think of two similar problems?
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17. Strategies
Divide and Conquer!
Break up a large problem into smaller units and solve each smaller
problem
• Applies the concept of abstraction
• The divide-and-conquer approach can be applied over and over again until
each subtask is manageable
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18. Algorithms
Algorithm
A set of unambiguous instructions for solving a problem or
subproblem in a finite amount of time using a finite amount of
data
Why must instructions be unambiguous?
Why must time and data be finite?
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19. Computer Problem-Solving 19
Analysis and Specification Phase
Analyze
Specification
Algorithm Development Phase
Develop algorithm
Test algorithm
Implementation Phase
Code algorithm
Test algorithm
Maintenance Phase
Use
Maintain
Can you
name
a recurring
theme?

20. Phase Interactions 20
Should we
add another
arrow?
(What happens
if the problem
is revised?)

21. A Tempting Shortcut? 21
GOAL
THINKING
CODE
REVISE
REVISE
REVISE
DEBUG
DEBUG
DEBUG
TEST
CODE

22. Developing an Algorithm
Two methodologies used to develop computer solutions to a problem
• Top-down design focuses on the tasks to be done
• Object-oriented design focuses on the data involved in the solution
But first, let's look at a way to express algorithms: pseudocode
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23. An Algorithm is . . .
• a step-by-step procedure for solving a problem in
a finite amount of time.
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24. Pseudocode
Pseudocode
A way of expressing algorithms that uses a mixture of English
phrases and indention to make the steps in the solution explicit
There are no grammar rules in pseudocode
Pseudocode is not case sensitive
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25. Example of algorithm
• In this example, we design an algorithm to find the perimeter and
area of a rectangle.
• To find the perimeter and area of a rectangle, you need to know
the rectangle’s length and width.
• The perimeter and area of the rectangle are then given by the
following formulas:
• perimeter = 2 * (length + width)
• area = length * width

26. The algorithm to find the perimeter and area of
the rectangle is:
1. Get the length of the rectangle.
2. Get the width of the rectangle.
3. Find the perimeter using the following equation:
perimeter = 2 * (length + width)
4. Find the area using the following equation:
area = length * width

27. Problem-Solving Phase
• ANALYZE the problem and SPECIFY what the
solution must do
• develop a GENERAL SOLUTION (ALGORITHM) to
solve the problem
• VERIFY that your solution really solves the
problem
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28. Implementation Phase:
Program
• translating your algorithm into a programming
language is called CODING
• with C++, you use
Documentation -- your written comments
Compiler -- translates your program
into machine language
Main Program -- may call subalgorithms
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29. Implementation Phase: Test
• TESTING your program means running (executing)
your program on the computer, to see if it produces
correct results
• if it does not, then you must find out what is wrong
with your program or algorithm and fix it--this is called
debugging
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30. Maintenance Phase
• USE and MODIFY the program to meet changing
requirements or correct errors that show up in
using it
• maintenance begins when your program is put
into use and accounts for the majority of effort on
most programs
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31. Some C++ History
• 1972 : Dennis Ritchie at Bell Labs designs C and 90% of UNIX is
then written in C
• Late 70’s : OOP becomes popular
• Bjarne Stroustrup at Bell Labs adds features to C to form “C
with Classes”
• 1983 : Name C++ first used
• 1998 : ISO/ANSI standardization of C++
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32. Three C++ Program Stages
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myprog.cpp myprog.obj myprog.exe
SOURCE OBJECT EXECUTABLE
other code
from libraries,
etc.
written in
machine
language
written in
machine
language
written in
C++
via compiler via linker

33. Basic Control Structures
• a sequence is a series of statements that execute
one after another
• selection (branch) is used to execute different
statements depending on certain conditions
• Looping (repetition) is used to repeat statements
while certain conditions are met.
• a subprogram is used to break the program into
smaller units
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34. SEQUENCE 34
Statement Statement Statement . . .

35. SELECTION (branch) 35
IF Condition THEN Statement1 ELSE Statement2
Statement1
Statement
Condition . . .
Statement2

36. LOOP (repetition) 36
WHILE Condition DO Statement1
Statement
Condition
. . .
False

37. SUBPROGRAM (function) 37
SUBPROGRAM1 . . .
SUBPROGRAM1
a meaningful collection
of SEQUENCE,
SELECTION, LOOP,
SUBPROGRAM

38. Computer Components
Central Processing Unit ( CPU )
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Control Unit
Arithmetic Logic Unit
Peripherals
Auxiliary
Storage
Device
Memory Unit ( RAM & Registers )
Input Device
Output Device

39. Memory Organization
• two circuit states correspond to 0 and 1
• bit (short for binary digit) refers to a single 0 or 1.
Bit patterns represent both the computer
instructions and computer data
• 1 byte = 8 bits
• 1 KB = 1024 bytes
• 1 MB = 1024 x 1024 = 1,048,576 bytes
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40. How Many Possible Digits?
• binary (base 2) numbers use 2 digits:
JUST 0 and 1
• decimal (base 10) numbers use 10 digits: 0
THROUGH 9
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