1. INTRODUCTION TO COMPUTER SCIENCE
CONCEPTS AND
PROGRAMMING
CPSC 206

2. Outline Part I: an overview of computer science.
Part II: computer hardware and software.
Part III: computer languages.

3. Part I: An Overview of Computer Science

4. What is Computer Science?
The study of how to solve problems with computers:
design and build a computer
- architecture, electrical engineering
use and share the computer efficiently
- operating systems
know if your problem is solvable
- computability theory

5. Computability Theory Motivated by 2 fundamental questions.
1) What is an Algorithm?
2) What are the capabilities &
limitations of algorithmic
computation?
Area of research for mathematicians & logicians since the 1930’s.

6. communicate a solution to a computer:
- programming languages, compilers, semantics

7. Semantics of a programming language.
Associates a meaning with each syntactically valid construct.
Describes the actions that will occur when the program associated with any valid construct in the language which is executed by a computer.

8. analyze your solution for correctness and efficiency
know if your solution is optimal
- complexity theory

9. Complexity Theory From computability to complexity, attention
shifts from exhibiting the existence of algorithms
to analyzing their efficiency .
The performance is measured by the resources
required by a computation. “How much
question”.
A solvable problem may have No practical
solution: every solution may require an
unacceptable amount of resources.

10. find a solution automatically
-artificial intelligence (make your solution easier for people to use)
- computer-human interaction
solve BIG problems
- software engineering
exploit multiple computers
-parallel and distributed systems, networking

11. Software Engineering Real-life programs are usually
large (thousands of lines of code)
created by teams of people
modified over the course of years
Rules and methods are needed to cope with this complexity.
Computer Science is more than Programming!

12. Part II: Computer Hardware and Software

13. Outline The development of modern computer systems.
Computer organization.
Solving problems on computers.
Programming and software engineering.

14. The Development of Modern Computer Systems
Early electronic computers
Mainframes
Time sharing
Microcomputers
Networked computing

15. Early electronic computers
ENIAC (1946) - Electronic Numerical Integrator and Calculator:
First general purpose purely electronic digital computer.
Built for US Army to make calculations for weather predictions & ballistics tables.
18, 000 vacuum tubes, space 50 X 30 ft, weighed 30 tons.
Numbers are entered by manually setting its 6000 switches.

16. EDVAC - Electronic Discrete Variable Calculator
A general instruction set and a stored program.
Both numbers and program instructions were stored electronically in the computer’s memory.
UNIVAC - Universal Automatic Computer
First commercially built computer.
Delivered to the U.S. Census Bureau in 1951 to tabulate the results of the previous year’s census.

17. John von Neumann (1903-1957) “von Neumann machine”.
Binary number computation.
Memory for data storage.
Input and output devices.
Overall logical control.

18. Mainframes Generation Architecture
The development of modern computers is often described in terms of the “generation”, in which a particular technology was used.
Architecture
The overall design of a computer’s electronic circuitry and its logical functionality is called its architecture.

19. First generation – 1950s Architecture Stored program
Electronic circuitry: vacuum tubes.
Memory: magnetic cores.
Stored program
Program: machine language.
Processing: a single program at a time.
Peripheral devices
Input and output: punched cards.
Data storage: magnetic tapes.

20. Second and third generations – 1960s
Architecture
Electronic circuitry: transistors to integrated circuits (ICs).
Symbolic languages
Assembly language.
FORTRAN - FORmula TRANslation, first high-level language.
COBOL - Common Business-Oriented Language.
LISP - LISt Processing.

21. Translators: translating high-level language to machine-understandable form:
Assemblers: converting program instructions from assembly languages into the machine language.
Compilers: translating program statements from FORTRAN and COBOL to machine language.
Interpreter: translating and executing each program statement dynamically.

22. Operating Systems (OS): a program to control the overall processing of the machine.
Batch processing: jobs that were similar in their requirements were grouped together into batches and run sequentially.
JCL (Job Control Language): to minimize operator intervention, JCL cards were inserted between the card decks of each job to direct how each job was to be processed.
Mass storage: disk drives provided permanent storage and fast access to large quantities of data.

23. Time Sharing
Time sharing controls computer operations in such a way that input and output activity (I/O) would not slow down the primary computation.
Multiprocessing (mid-1960s)
A program was broken into tasks (processes).
Each process was allow a interval of time for execution before control was passed to another one.
Interactive computing (early 1970s)
User could sit at a remote terminal and communicate directly with the computer.
Allow multiple users at the same time.

24. Microcomputers Fourth generation – 1970s Minicomputers – 1970s
Chip circuitry: VLSI - Very Large Scale Integration, which could contain all logic circuits on a single chip. These chips were known as microprocessors.
Minicomputers – 1970s
Lower cost and more accessible computing power.
Architecture is based on the 16-bits (vs. the 32-bits in use for larger computers) representation of data in computer memory.

25. PC - Personal Computer – 1970s-1980s
Low cost computers intended for personal use.
Input: keyboard.
Output: screen.
Data storage: removable floppy disks.
Examples: Apple, IBM PC.
DOS - Disk Operation System
DOS was developed by Microsoft for the IBM PC.
DOS provides the basic functions for a single user to handle data storage and to control input and output devices and program execution.

26. GUI – Graphical User Interface:
With the introduction of the Mac (Macintosh) computer by Apple in 1984.
Information was presented to the user via pictures, known as icons.
A new hand-held input device, called a mouse, was available for selecting choices from the screen.
Mac utilized a bit-mapped display which is able to display both graphics and text.
Each graphical image is composed of small dots called pixels which must be manipulated individually by the computer ‘s programs.

27. PC software:
Software are programs directing a computer’s operations and solving problems.
Hardware are the physical devices that form the computer itself.
The popularity of PCs grew rapidly in the 1980s as innovative application programs were developed to enable nontechnical users to do useful tasks on the computer.

28. Word processors allow a user to write and edit text.
Spreadsheet programs provider convenient computational power for data stored in tables.
Business graphics programs are able to display data in the form of graphs and charts.

29. Workstations – 1980s
For complex number crunching scientific and engineering programs.
For a single user.
Using multiprocessing systems.
Well suited for networking use.

30. Networked Computing Computer networks – 1980s-present Telephone lines
Users access computers which are at a distance.
Users share data.
Users transmit messages between computers.
Telephone lines
An electronic device called a modem allows computers to transmit data over telephone lines,

31. LAN – Local Area Network
A LAN allows computers in reasonable proximity of each other to be connected by cabling over which data can be transmitted from one machine to another without the use of telephone lines.
Distributed computing
Techniques of shared processing over networks are generally called distributed computing.
A computer that provides the core of the services is called a server.
Any computer requesting a service is known as a client.

32. Computer Organization
Data representation
Main Memory
Central Processing Unit

33. Data Representation
The information which a computer processes is generally known as data.
Individual data values may represent numbers, alphabetic characters, or other coded information.
The computer programs are also data, because the instructions which they contain must be stored in the computer’s memory before they are able to be processed.

34. All data is stored and processed in binary form, that is, as a series of 0s and 1s.
Each binary digit, called a bit, represents the smallest unit of information which can be stored in the computer.
Bits are grouped into longer units known as bytes to hold more meaningful data.
1 byte = 8 bits

35. Two standard coding systems for representing a byte.
ASCII – American Standard Code for Information Interchange
Hello 
H –
EBCDIC – Extended Binary Coded Decimal Interchange Code:
Hello 

36. Main Memory
Main memory is that part of a computer’s electronic circuitry which holds the binary data which the computer’s program will process.
Memory is divided into cells.
Each cell is assigned a specific address, from 0 to the maximum size of the computer’s memory capacity.

37. The size of a computer’s memory is the number of the addressable cells it contains.
Bit 1
Byte 8 bits
Kilobyte 210 bytes 1,000
Megabyte 210 kilobytes ,000,000
Gigabyte 210 megabytes 1,000,000,000
Terrabyte 210 Gigabytes 1 trillion
e.g. A 256K bytes of memory have 256*1024=262,144 bytes.

38. ROM – Read-Only Memory, is a specialized part of main memory which is designed to prevent data loss when the power to the computer is turned off.
Read-Only.
Permanence.
Typical use: ROM is reserved for critical program instructions which must be immediately available when a computer is first turned on.

39. Central Processing Unit
CPU is the heart of a computer.
Control unit has the overall task of controlling and coordinating the computer’s operations.
Arithmetic/Logic Unit (ALU) performs all arithmetic computations and logic operations.

40. Control unit: Program execution:
Each computer has a unique instruction set determined by the designers of its architecture. Each instruction includes a code that specifies the operation to be performed, and the memory address of the data value to be acted on.
All the operations of a computer are directed by a set of instructions, known as a program, which is stored in the computer’s main memory.
The control unit locates the appropriate instructions, controls their sequencing, and executes them by activating appropriate circuitry.

41. Program Counter (PC) is a special-purpose memory location which always contains the memory address of the instruction that is currently being executed.
Instruction counter (IC) is another special-purpose memory cell which contains the instruction currently being processed.

42. Hardware characteristics
CPU synchronizes its operations by the regular pulses emitted by an electronic device called a clock.
The speed of a computer can be quoted as:
Clock speed, e.g. 100MHz means 100 million cycles per second.
MIPS, a million instructions per second

43. Arithmetic/Logical Unit (ALU) performs all arithmetic computations and logical operations.
Arithmetic - Add, subtract, multiply, divide
exponentiation etc.
Logical - Testing for relationships.
A<B; Name = ‘mary’;
c>=10; possible Answers? True or False
The ALU contains special memory cells, known as registers, in which the arithmetic is carried out.

44. CPU
reads the individual program
instructions from main memory. Executes the instructions 1 at a time until completion
Fetch - Decode - Execute
The machine cycle algorithm is continuously repeated until program termination.
Machine Cycle

45. Fetch:
Retrieve the next instruction from memory [where the command is located (address) is stored in a register called the program counter]
update the program counter to the address of the next instruction.
The instruction just Fetched is placed in the instruction register

46. Decode: Execute: Decode the Bit pattern in the instruction register
Having decoded the instruction, the control unit enters the execute phase. It activates the correct circuitry to perform the requested task.
Decode:
Execute:

47. If the instruction is a load from memory, the Control unit causes the load to occur.
If the instruction is for an arithmetic operation, the control unit activates the appropriate circuitry in the ALU with the correct input stored in registers.
When the instruction has been executed, the control unit again begins the machine cycle with the Fetch cmd (the address of the next cmd is in the program counter)

48. Diagram of Architecture
CPU R1
PC R2
IC R3 R4
control unit ALU
bus

49. Diagram of Architecture (cont.)
First second third
Instr Instr Instr. … …… ..
data
memory

50. Solving Problems on Computers

51. Designing Modular Solutions
Top-down
Start with what you want
Cut it up in parts
If the parts are trivial to solve, then solve them
If the parts are non trivial, apply top-down again
You will cut up the problem in smaller and smaller sub-problems until they can be solved trivially.
Bottom-up
Start with what you small parts
Put them together to form large parts
Until you end up with the thing that you wanted

52. Designing Modular Solutions
Problem with top-down design
You must know how you break the problem up.
You need intuition to tell you that this is the right way to divide the problem into sub-problems.
Problem with bottom-up design
Where do you start?
Usually used in an evolution way, thus systems start simple, functionality increases as time goes by.

53. An example of top-down design
Compute Tax
Compute adjusted
gross income
Compute
deductions
Compute
credits
Compute
adjustments
Compute
Income
Interest &
dividends
Business
income
Wages
Capital
gains
Misc.
Income

54. Algorithm Development
An algorithm is a specification of the series of steps which must be followed in order to solve a problem or accomplish a task.
Algorithm development

55. IPOS Cycle I - Input Implies 3 Questions Input what? Input how?
Input where?

56. Input What? Program & Data
Program [Load Module] in machine code form after being compiled & Linked
e.g.
05C0 5820C00E Hexidecimal Notation
in Binary form
etc.
0 5 C 0

57. string data numeric data
e.g. Program to calculate a students avg grade
string data numeric data
Bob
will store data using:
Binary coding scheme
ASCII or EBCDIC

58. How input? Where input? Memory of Computer
Input Devices: Floppy disk, Magnetic Tape Drive, Disk Drive, CRT, Voice, Light pen, Scanners etc.
Where input?
Memory of Computer
has evolved over the computer hardware generations.

59. P- processing 2 categories Arithmetic - Add, subtract Multiply, Divide
Exponentiation
Trig functions
etc.
Logical - Testing for relationships.
A<B; Name = ‘mary’;
c>=10; possible Answers?
True or False

60. Output - What? Hard copy: physical, tangible, portable. Print outs.
Soft copy: visual, CRT displays
Output devices: printers, floppy disk, Mag tape, Mag disk, voice, etc.

61. S - Secondary Storage Medium
Long Term Storage: Disks, Tapes, etc.
What - Program Itself
Program output

62. Example
An algorithm for a program converting Fahrenheit temperature values (F) to Celsius degrees (C).
Input{Processing}OutputStorage 
F{apply F to C conver. form.}CDisk
C = 5/9*(F-32)

63. Algorithm Representation
Pseudocode
The steps of an algorithm are sometimes written in English in a shorthand form called pseudocode.
There are no rules for writing pseudocode.
It is purpose is to summarize the steps of the solution and to make the logical sequence of a program clear.

64. locate a student’s scores | compute the average quiz score
An Example A professor who is about to write a program to assign
grades to the students in his Programming in C course might express
his final grade algorithm in the following pseudocode.
locate a student’s scores |
compute the average quiz score
compute the average homework score
if the midterm exam was a make-up
then reduce the exam score by 10%
compute the student’s course grade
post the student’s course grade

65. Algorithm Representation (cont.)
Flowcharts
For the problem whose solutions involve decision and repeated steps.
Flowcharts typically show a program’s logic.
Symbols:
Input/Output
Start/stop
Processing
Decisions
Flow of control

66. An Example An algorithm to control an Automatic Teller Machines (ATMs).
Start
Read card no
Correct pwd?
Reject card
yes
Deposit
Inquire
Access account info
Withdraw ……
Stop

67. Algorithm Representation (cont.)
Decision Trees
An example A telephone company bases its rates for long distance calls on the time of day and day of the week when a call is made.
8am to 5pm
5pm to 11pm
11pm to 8am
full rate
evening rate
night rate
Weekday
Long
distance
charges
8am to 5pm
5pm to 11pm
11pm to 8am
night rate
evening rate
Saturday
Sunday
Weekend
night rate

68. Programming Programming
Programming is the process of translating a problem’s solution into instructions that a computer can process.
Software life cycle
Analysis: analyze the problem.
Design: use top-down or bottom-up.
Implementation: use hardware and/or software.
Testing: try it in the lab.
Maintenance: keep it working.
Programming

69. Programming (cont.) Paradigms Procedural programming
Gives commands to do things.
These commands change the state.
Declarative programming
Givens definitions of operations.
Tells the system what you want to know, and it will figure it out.
Object oriented programming
Like procedural, but has operations on objects only.
Operations change the state of an object.

70. Programming (cont.) Example languages Procedural Declarative
C, Pascal, Basic, FORTRAN, COBOL, Ada…
Declarative
LISP, Prolog, …
Objected oriented
Smalltalk, Java, C++,

71. Part III: Computer languages

72. Why computer language? Compute are stupid.
They do not “understand” things.
They have to be told very precisely what to do.
Natural language are ambiguous.
“College Station’s largest (quality (free) newspaper)”.

73. Why computer language? (cont.)
Programming language are designed to be unambiguous.
They are defined precisely, by syntax and semantics.
The meaning of each program is defined precisely.
Priority of operators is defined, e.g., 2+3*4 means 2+(3*4).
Associativity is defined, e.g., means (2-3)-4.

74. A brief history of C BCPL was developed by Martin Richards
B was developed by Ken Thompson
C was developed and implemented by Dennis Ritchie on a DEC PDP-11 in the 1970s.
The ANSI C standard was adopted in 1989.

75. C is a middle-level language
C combines the best elements of high-level language with the control and flexibility of assembly language.
C allows the manipulation of bits, bytes and addresses.
C is portable. Portability means that it is easy to adapt software written for one type of computer or operation system to another type.
C has only a small number of keywords. ANSI C defined 32 keywords (BASIC has over 100!).

76. C’s place in the world of programming languages
High level Ada, Modula-2, Pascal, COBOL, FORTRAN BASIC
Middle level Java, C++, C, FORTH,
Macro-assembler
Low level Assembler

77. C is a structured language
Compartmentalization of code and data. This is the ability of a language to section off and hide from the rest of the program all information and instructions necessary to perform a specific task.
Use of subroutines that employ local variables.
Use of code block.
if (X<10) {
printf(“Too low, try again.\n”);
scanf(“%d”, &x); }

78. C is a structured language (cont.)
Use of procedures & functions.
No use of go-to statements.
By use of structured languages it was for the first time possible to write moderately complex programs fairly easily.
No structured
FORTRAN, BASIC, COBOL
Structured
Pascal, Ada, C++, C, Java…

79. ‘C’ was considered by many to be the best language implemented with a structured approach. Its creation was a direct result of the need for a structured, efficient, high-level language that could replace assembly code when creating systems programs.

80. It is a programmers language developed by professional programmers.
It is a powerful, efficient, structured language that is relatively easy to learn.
It is a programmers language developed by professional programmers.
Few restrictions, block structure, stand-alone functions, a compact set of keywords.
During the late 1970’s & early 80’s “C” became the dominant computer programming language, still widely popular.
Initially, C was used for systems programming, which forms a portion of the operating system or its utilities, such as editors, compilers, linkers.
Now C is used to program all tasks.