CPS120 Introduction to Computer Science

1
CPS120 Introduction to Computer Science

• Exam Review
• Lecture 9

2
Introduction To Computers
3
System Components

• Hardware
• I/O devices (input/output)
• keyboard, mouse, monitor, etc.
• CPU
• Primary Storage
• Secondary Storage
• Software

4
Storage Devices

• Primary storage
• RAM (Random Access Memory, or just memory for
  short)
• active data that is being stored, lost if power
  is cut off so save often
• ROM (Read-Only Memory)
• commands that are permanently stored on chips
• PCs use BIOS, Macs use the Toolbox
• Secondary storage
• Hard disk, floppy disks
• Slower method of storage retrieval but safer

5
Representing Data Bits

• Computer only uses on off within its
  circuits
• Binary number system
• On, 1, high state of electricity
• Off, 0, low state of electricity
• Bits (0s and 1s)

6
Typical System

• Computer case
• Monitor
• Printer
• Speakers
• Modem
• Keyboard
• Mouse

7
Types of Ports

• Parallel port 25 holes female connector LPT1
  printer or storage devices
• Monitor port
• Keyboard port
• Serial port 9 or 25 pins male connector COM1
  mouse or modem
• Game port
• Network port
• USB port
• 127 devices
• Printer, modem, joy stick

8
Types of Printers

• Ink-jet has a print head that sprays ink through
  tiny nozzles onto a page
• 2 to 10 pages (ppm)
• 360 to 2400 dots per inch
• Color printers spray cyan, magenta, yellow and
  black to create different colors
• Laser-printer
• Works like a photo copier
• Speed of 4 to 16 pages
• Have a CPU
• 600 to 2400
• Memory 2mb to 8 Mb

9
Communications

• Modems let a computer exchange information
  through telephone lines
• Speed of a modem determines how fast it sends and
  receives messages
• 56,000 bps (56 Kbps)
• V.90 standard receive 56K and send 33.6K
• Speed at which information flows depend on the
  quality of the phone line
• A modem needs a communications package to manage
  the transmission of information
• Data compression squeezes together data

10
High-speed Connections

• ISDN Integrated Services Digital Network
• Digital phone line
• 56 Kbps to 128 Kbps
• Cable Modem
• Same cable as TV
• 4000 Kbps
• DSL Digital subscriber line
• High speed digital phone line
• 1000 6000 Kbps
• Satellite

11
USB and Firewire

• High-speed ports that allow information to
  quickly transfer between a computer and an
  external device
• USB
• Supports up to 127 device
• USB 1.0 12 megabits per second
• USB 2.0 480 Mbps
• FIREWIRE
• 63 devices at 400 Mbps
• Can purchase Firewire expansion card

12
CPU (Central Processing Unit)

• Processes instructions, performs calculations,
  and manages the flow of information
• Performance
• CPU speed is a major factor in determining how
  fast a computer operates (faster the speed,
  faster computer operates)
• Measured in megahertz (MHz) A clock cycle relates
  to the clock that controls the timing in the
  microprocessor.
• For example, a 900MHz (megahertz) clocked
  microprocessor generates 900 million clock cycles
  per second.
• Each generation of CPU is more powerful than the
  one before. It's clock cycles are faster at a
  given speed

13
BUS

• Electronic pathway that carries information
  between devices in a computer
• Bus Width (think lanes of a highway)
• 8 bits is one character
• Bus Speed (think speed limit)
• Measured in MHz (millions of cycles per second)

14
Processing

• Random Access Memory Temporarily stores data
  inside a computer
• Constantly overwritten
• Measured in megabytes (MB)
• 64 minimum these days100 MHz (millions of cycles
  per second)
• Dynamic RAM is type of memory chip that makes up
  memory in many computer systems. Access speed
  measured in megabits
• Most system boards can support access speed of
  Single Inline Memory Module (SIMM) 9 memory
  chips
• Dual Inline Module (DIMM) 18 memory chips
• If you have limited memory or you have many
  programs open, your computer may need to use part
  of the hard drive to simulate more memory

15
Using Memory Cache

1. Look through documents on your desk (internal
   cache)
2. Look through documents in your desk drawer
   (external cache)
3. Looking through documents in your filing cabinet
   (RAM)

16
Relation of Cache Hard Drives

• Disk cache speeds up the computer by storing the
  data the computer has most recently used
• Constantly updated
• Area of memory
• Fast access
• Then hard drive is searched

17
Hard Drives

• Magnetically stores data on rotating disks called
  platters
• Stores your operating system and programs
• Document will not be lost when you turn off the
  computer
• Capacity is measured in bytes
• Speed is measured in revolutions per minute

18
CD-R CD-RW Drives

• CD-R (Compact Disc Recordable)
• Permanent store not erasable
• CD-RW
• Can be erased and rewritten
• Read / Write and Re-write speeds
• Usually 74 minutes
• Special software needed to record onto a disk
• Referred to as burning a CD

19
DVD-ROM Drive

• DVD Digital Versatile Disk
• Generally cannot change the information stored on
  a disk
• Similar to CD but stores more information
• Speed determines transfer rate (6 X)
• Capacity
• 1 side / 1 layer 4.7 GB
• 1 side / 2 layer 8.5 GB
• 2 sides / 1 layer 9.4 GB
• 2 sides / 2 layers 17 GB

20
Removable Storage Devices

• Jazz Drive 2 GB
• Zip Drive 250 MB
• LS-120 Drive 120 MB

21
Databases

• Organized in
• Tables
• Collection of information about a specific topic
• Field
• Category of information
• Record
• Single instance of information

22
Operating Systems

• Software that controls the overall activity of
  the computer
• Ensure that all of the parts of the computer work
  together smoothly
• Functions
• Control hardware
• Run software
• Manage information
• Programs that run on one operating system
  platform do not generally run on others

23
Characteristics of Specific OS

• DOS
• Windows 3.1
• Windows 9X
• Windows ME
• Windows XP
• Windows NT/2000
• MAC OS9 10
• UNIX
• LINUX

24
Compilers

• An engine that works on your behalf to process
  instructions and allow you to deal with various
  basic rules of the language
• The compilers job is to make sure you follow the
  rules, to require that you provide enough
  information that the compiler can translate you
  instructions into languages the components can
  understand

25
Interpreter vs. Compiler

• Interpreter
• Translates instructions to machine code
  line-by-line.
• Compiler
• Translates the entire program to machine code
  before running it.

26
What Is a Network

• A network is a group of connected computers that
  allow people to share information and equipment

27
Physical Networking

• Hubs
• A hub is a device that provides a central
  location where all the cables on a network come
  together
• NICs (Network Interface Card)
• An expansion card that physically connects each
  computer to the network
• Cables
• Coaxial, Unshielded Twisted Pair (UTP), Shielded
  Twisted Pair, Fiber-optic
• Wireless

28
Client-Server Networks

• Used for large networks
• Files are stored on a central computer and
  everyone who can access the network can be given
  access them
• Easy to create scheme to backup and protect files
• Client a computer that can access information
  stored on the server
• Server Central computer that stores files
• NetWare, UNIX, Windows NT/2000

29
Peer-to-Peer

• Used for a small number of computes (e.g. 10)
• Files stored on own computers access given to
  them to others on the network
• LANtastic, Windows-98, Windows-ME

30
Information Exchange

• Ethernet
• Most popular and least expensive solution
• Each computer waits for a pause before sending
  information
• Like polite conversation
• Collisions between information often occur
• Computers wait a moment, then resend
• Ethernet 10 Mbps, Fast Ethernet 100 Mbps,
  Gigabit Ethernet 1000 Mbps

31
Information Exchange

• Token-ring is a type of network where a token
  that collects and delivers information is passed
  from compute to computer
• Speeds of 4 or 16 Mbps
• Asynchronous Transfer Mode (ATM) is a type of
  network that works by sending information in
  equal-sized pieces called cells
• 25, 155, 622 or 2488 Mbps
• Often networks networks

32
Intranet

• Small version of the Internet in a company
• Uses familiar web-browsers and email packages
• Allows hyper-linking
• VPNs (Virtual Private Network)
• End-to-end encryption
• More cost efficient than private lines

33
World Wide Web

• Part of the Internet consisting of a huge
  collection of documents stored on computers
  around the world
• Web server computer that stores and delivers web
  pages
• Web site collection of web pages
• URL (Uniform Resource Locator) unique address
• HTTP, Computer, Directory, Name of Page
• Hyperlinks jump to different web pages

34
Creating Good Passwords

• In order to be useful in authentication and
  authorization, a password should meet the
  following criteria
• Passwords must be at least six characters
• Passwords must include three of four types of
  characters
• Uppercase letters
• Lowercase letters
• Numbers
• Non-alphabetic characters such as punctuation
  marks
• Passwords shouldn't contain personal information

35
Pass-phrases

• If you are serious about good password security,
  get in the habit of using pass-phrases. For
  example, it is easy enough to remember a phrase
  like born on the 4th of July, but creating a
  password from it like bot4thoJ would create a
  password that meets the criteria discussed above.

36
Virus Definition

• A computer virus is a computer program that can
  infect other computer programs by modifying them
  in such a way as to include a copy of itself. A
  virus, by definition, can't exist by itself. It
  must infect an executable program.
• A simple virus that can make a copy of itself
  over and over again is relatively easy to
  produce. Even such a simple virus is dangerous
  because it will quickly use all available memory
  and bring the system to a halt.

37
Other Types of Viruses

• An e-mail virus is not any different from a
  regular virus it just has a different mode of
  transportation ILOVEYOU"
• Melissa
• Script viruses are destructive code that does its
  damage by executing a program on a client machine
• A macro virus is a type of computer virus that is
  encoded as a macro embedded in a document

38
Anti-Virus Software

• Anti-viral software can be set up to run
  automatically each time you boot up the machine
  or run an executable. You can also execute
  anti-viral software manually if you suspect you
  have had a problem or you have received a
  suspicious attachment or some sort of un-trusted
  media.
• There are two parts to most pieces of anti-viral
  software the engine and the definitions.
• The definitions change all the time. This is the
  part of anti-viral software that needs to be
  updated constantly, because the population of
  viruses changes rapidly, with newly developed
  viruses springing up along with minor
  modifications of existing viruses (mutations)
  appearing constantly.
• The engine, on the other hand, is static and
  changes only at major release points. The engine
  is the driving force behind a virus program that
  checks for virus signatures on you machine and in
  your software.

39
Stay Current

• The program you use isn't as important as how
  often you use it and that you keep it updated
  with the most recent virus definitions
• To be effective, antiviral software must be
  current -- even two-month-old software can be
  dangerously outdated

40
Other Types of 'Malware'

• A worm is a special type of virus that can
  replicate itself and use memory, but cannot
  attach itself to other programs
• 'Code Red'
• Nimda
• A Trojan horse is a program that pretends to do
  something useful, but instead does something
  nefarious.
• Trojans aren't infectious
• Often they place executables on the drive

41
Hardening Your System

• The term "hardening" refers to the process of
  configuring software so as to minimize potential
  security risks
• Hardening security-specific applications like
  firewalls, intrusion detection systems, and
  antiviral tools involves turning on features and
  setting restrictive access rules

42
Your Security Profile

• A port is an interface on a computer to which you
  can connect a device
• A port is an endpoint to a logical connection
• The port number identifies what type of port it
  is
• Personal computers have various types of ports.
  In this context
• A key to determining your computers security
  profile is to determine port usage

43
How do Firewalls Work?

• A firewall is analogous to a moat around a
  medieval castle. In essence, the moat and
  drawbridge represent a "choke" point for all
  traffic in and out
• A single point is much easier to monitor and can
  be closed if needed
• All messages entering or leaving the intranet
  pass through the firewall, which examines each
  message and blocks those that do not meet the
  specified security criteria

44
How Does it Work Technically?

• Firewalls act as proxy servers, by masking the
  address of internal machines
• Or packet filters using a "wall of code" that
  inspects each individual "packet" of data as it
  arrives at either side of the firewall

45
Different Types of Backups

• Different types
• Full
• Incremental
• Differential

46
Introduction to Programming
47
The Program Development Cycle
48
What Can a Program Do?

• A program can only instruct a computer to
• Read Input
• Sequence
• Calculate
• Store data
• Compare and branch
• Iterate or Loop
• Write Output

49
Fundamental Programming Concepts

• Assignment of values to a variable
• Iteration (Looping)
• Over a set of set of statements
• With respect to a logical expressions
  (conditions)
• Delegation of sub-tasks to functions / procedures

50
The Structure Theorem

• The Structure Theorem states that any algorithm
  can be built from three basic control structures.
  
• One-after-another (Sequence)
• Decision-making (Selection)
• Making choices between 2 or more alternatives
• Repetition (Iteration)
• Concerned with repetitive tasks (and the
  termination conditions of loops)

51
What is an Algorithm?

• An algorithm is merely the sequence of steps
  taken to solve a problem
• Two parts
• Actions to be executed
• Order in which those actions are to be done
• Computational steps that transform the input data
  into useful output data.
• Algorithms are not programs
• They need to be coded in a programming language
  like C

52
Pseudocode Flowcharts are Important

• Pseudocode
• Make a detailed description of your algorithms
  logic before worrying about C syntax and data
  layout.
• An algorithm you develop using pseudocode should
  be capable of implementation in any procedural
  programming language
• Pseudocode is generally independent of the
  implementation language
• Flowcharts
• A graphical layout of the algorithm is often very
  useful in spotting illogical logic!

53
Reasons Programmers Draw Flowcharts

• Drawing a flowchart gives the programmer a good
  visual reference of what the program will do
• Flowcharts serve as program documentation
• Flowcharts allow a programmer to test alternative
  solution to a problem before coding
• Flowcharts provide a method for easy desk checking

54
Common Flowchart Symbols
55
Rules for Drawing Flowcharts

• Top to bottom and left to right
• Draw the flowchart the way you like to read
• Use arrowheads on flow lines whenever the flow is
  not top to bottom, left to right
• Be neat ! Use graphics software
• Avoid intersecting lines

56
Disadvantages to Flowcharts

• Time consuming
• A program flowchart shows how the input becomes
  output, but it does not show why a particular
  step is done
• Flowcharts are subjective

57
Pseudocode

• This device is not visual but is considered a
  first draft of the actual program.
• Pseudocode is written in the programmers native
  language and concentrates on the logic in a
  programnot the syntax of a programming language.

58
General Rules for Pseudocode

• There is no standard pseudocode
• The rules of Pseudocode are generally
  straightforward
• Should be easily read and understood by
  non-programmers
• All statements showing "dependency" are to be
  indented.
• These include while, do, for, if, switch

59
Pseudocode Statement Rules

• Statements are written in a simple English-like
  language
• Each instruction is started on a separate line
• Logic-showing keywords are written in UPPER CASE
  or typed in BOLD UPPERCASE
• (e.g. IF, THEN, FOR, DO etc.)
• These are the only uppercase words in this form
  of pseudocode.
• Indentation is used to show structure
• Instructions are written from top to bottom, with
  only one entry point and one exit point
• Logically related groups of instructions can be
  formed into modules and given a name

60
Rules for Pseudocode

1. Make the pseudocode language-independent
2. Indent lines for readability
3. Make key words stick out by showing them
   capitalized, in a different color or a different
   font
4. Punctuation is optional
5. End every IF with ENDIF
6. Begin loop with LOOP and end with ENDLOOP
7. Show MAINLINE first all others follow
8. TERMINAE all routines with an END instruction

61
Compilation Process

1. Get the set of instructions from you
2. Review the instructions to see if they violate
   the rules (syntax) of the language
3. If all the rules are obeyed, create a working
   file in the language of the computer (machine
   language)
4. Attach to the working file full instructions for
   any shortcuts you may have used (linkage)
5. Assemble a final file in machine language

62
Compiling and Debugging

• Executable code will not be created until you
  correct all of the syntax errors in your source
  code
• Then the fun (with logic errors) begins

63
Syntax Logic Errors

• A syntax error is simply the violation of the
  rules of a language misuse of structure and form
  in programming or a violation of the compilers
  rules. These errors are detected by the compiler
• Also know as 'fatal compilation errors'
• A logic error is a mistake that complies with the
  rules of the compiler that causes the program to
  generate incorrect output

64
Error Prevention Testing

• Use good design and programming style
• Don't use global variables
• Study your code before typing and running it
• Have someone else look at it
• Make your program self-documented
• Program defensively put in assertions and
  self-checking code and comment them out
• Test your code at boundary values for variables
• Log your bugs
• Test code in pieces using "stubs"
• Consider correctness, reliability, utility and
  performance

65
Semantic Error Detection

• Use the tracing method to display the value of
  critical variables
• Make the error reproducible
• Get a stack trace of function calls to verify
  sequencing
• Correct the error immediately when you find it
  and check if you made it somewhere else
• Examine your last code changes for errors
• Ensure that you have saved and run the corrected
  programs

66
Debugging

• Debugging is the process of locating and fixing
  or bypassing bugs (errors) in computer program
  code or the engineering of a hardware device.
• To debug a program is to start with a problem,
  isolate the source of the problem, and then fix
  it.

67
Debugging Steps

• Proofread before compiling
• Compile
• Correct all the obvious errors
• Start at the beginning of the list of errors and
  warnings
• A single syntax error may cause the compiler to
  believe numerous other syntax errors are
  occurring
• Look at the error lines and if you see the error,
  fix it. Otherwise, leave it for later. It may
  vanish when you fix something else
• Dont worry if more errors appear. Some errors
  mask other errors
• Recompile when you have fixed what you recognize

68
Debugging Steps

1. Repeat 3 4 until no further errors are obvious
2. Attempt to solve the remaining errors in a
   top-down fashion
3. Solve whatever errors you can without spending
   long periods of time on any given error
4. Recompile whenever you feel you dont see any
   further solutions

69
A Debugging Mindset

• Assume your syntax is wrong. Look it up!
• Add working comments as you change things
• If you are 100 sure a line is correct, then
  search for a syntax error in the lines ABOVE that
  line
• Start with the immediately previous line and work
  backward
• Never make a change you cant explain

70
Debugging Checklist

• Visually verify the spelling and case of keywords
  and identifiers
• -- Remember, in the editor, keywords are blue,
  literals are black and comments are green
• -- Look for problems with l and 1 and o and 0
• Verify syntax with a reference book, not just
  visually
• -- Dont trust your eyes you see what is
  supposed to be there
• Try to find an example in the reference book that
  does something similar and compare the code
• Verify that the necessary delimiters used for
  that line are there
• -- Check the lines above and below as well

71
Debugging Checklist

• Without looking at your source code or notes,
  rewrite the instruction on a piece of paper and
  then compare it to your actual code dont cheat
• Verify that the line is really the source of the
  error by commenting the line using //
• Dont worry about other errors that result from
  this
• If the error disappears, it probably results from
  the line you are working on
• If it moves to the next line it is probably
  caused earlier in the code
• Remember that the compiler cannot be trusted to
  pinpoint lines

72
Warnings

• Even though an executable has been generated, you
  may not be done with syntax errors
• Compilers generate syntax warning messages which
  are not fatal errors but represent special error
  checking functions for certain common programming
  errors

73
Linker Errors

• Not all syntax errors are detectable by the
  compiler
• These errors do not become apparent until files
  are put together to create an executable
• These errors are not linked to a specific line of
  code
• Look for the name of the variable and see what
  lines of code it occurs on using EDIT and FIND
• LNIK2001 unresolved external
• LNK1120 unresolved externals

74
Logic/Semantic Errors

• If the data is good and a program does not do
  what it is supposed to do, there must be at least
  one logic error present
• The syntax rules of C have been correctly
  followed, but the meaning of the code is
  incorrect

75
Semantic Errors

• A semantic error is a violation of the rules of
  meaning of a programming language
• E.g. My refrigerator just drove a car to Chicago
• Overt logic errors
• Something is obviously wrong even though the
  program is running
• Covert logic errors
• Not so obvious something is wrong
• Run things various ways to highlight these errors

76
Approaches to Correction

• Desk-checking
• Inserting Tracing Statements
• Used when program "crashes"
• Runs to completion with incorrect output
• Using an interactive debugger

77
Common Semantic Errors

• Infinite Loop
• Created when a loop in which the expression
  tested never becomes false
• Misunderstanding operator precedence
• Dangling else
• Off-By-One Error
• Loop that iterates one fewer or one more than is
  correct
• Code inside a loop that doesnt belong there
• Not using a compound statement when one is
  required
• Array index bounds error

78
Computer Mathematics
79
Representing Data

• The computer knows the type of data stored in a
  particular location from the context in which the
  data are being used
• i.e. individual bytes, a word, a longword, etc
• 01100011 01100101 01000100 01000000
• Bytes 99(10, 101 (10, 68 (10, 64(10
• Two byte words 24,445 (10 and 17,472 (10
• Longword 1,667,580,992 (10

80
Alphanumeric Codes

• American Standard Code for Information
  Interchange (ASCII)
• 7-bit code
• Since the unit of storage is a bit, all ASCII
  codes are represented by 8 bits, with a zero in
  the most significant digit
• H e l l o W o r l d
• 48 65 6C 6C 6F 20 57 6F 72 6C 64
• Extended Binary Coded Decimal Interchange Code
  (EBCDIC)

81
Decimal Equivalents

• Assuming the bits are unsigned, the decimal value
  represented by the bits of a byte can be
  calculated as follows
• Number the bits beginning on the right using
  superscripts beginning with 0 and increasing as
  you move left
• Note 20, by definition is 1
• Use each superscript as an exponent of a power of
  2
• Multiply the value of each bit by its
  corresponding power of 2
• Add the products obtained

82
Binary to Hex

• Step 1 Form four-bit groups beginning from the
  rightmost bit of the binary number
• If the last group (at the leftmost position) has
  less than four bits, add extra zeros to the left
  of the group to make it a four-bit group
• 0110011110101010100111 becomes
• 0001 1001 1110 1010 1010 0111
• Step 2 Replace each four-bit group by its
  hexadecimal equivalent
• 19EAA7(16

83
Converting Decimal to Other Bases

• Step 1 Divide the number by the base you are
  converting to (r)
• Step 2 Successively divide the quotients by (r)
  until a zero quotient is obtained
• Step 3 The decimal equivalent is obtained by
  writing the remainders of the successive division
  in the opposite order in which they were obtained
• Know as modulus arithmetic
• Step 4 Verify the result by multiplying it out

84
Representing Signed Numbers

• Remember, all numeric data is represented inside
  the computer as 1s and 0s
• Arithmetic operations, particularly subtraction
  raise the possibility that the result might be
  negative
• Any numerical convention needs to differentiate
  two basic elements of any given number, its sign
  and its magnitude
• Conventions
• Sign-magnitude
• Twos complement
• Ones complement

85
Representing Negatives

• It is necessary to choose one of the bits of the
  basic unit as a sign bit
• Usually the leftmost bit
• By convention, 0 is positive and 1 is negative
• Positive values have the same representation in
  all conventions
• However, in order to interpret the content of any
  memory location correctly, it necessary to know
  the convention being used used for negative
  numbers

86
Sign-Magnitude

• For a basic unit of N bits, the leftmost bit is
  used exclusively to represent the sign
• The remaining (N-1) bits are used for the
  magnitude
• The range of number represented in this
  convention is 2 N1 to 2 N-1 -1

87
Sign-magnitude Operations

• Addition of two numbers in sign-magnitude is
  carried out using the usual conventions of binary
  arithmetic
• If both numbers are the same sign, we add their
  magnitude and copy the same sign
• If different signs, determine which number has
  the larger magnitude and subtract the other from
  it. The sign of the result is the sign of the
  operand with the larger magnitude
• If the result is outside the bounds of 2 n1 to
  2 n-1 1, an overflow results

88
Twos Complement Convention

• A positive number is represented using a
  procedure similar to sign-magnitude
• To express a negative number
• Express the absolute value of the number in
  binary
• Change all the zeros to ones and all the ones to
  zeros (called complementing the bits)
• Add one to the number obtained in Step 2
• The range of negative numbers is one larger than
  the range of positive numbers
• Given a negative number, to find its positive
  counterpart, use steps 2 3 above

89
Twos Complement Operations

• Addition
• Treat the numbers as unsigned integers
• The sign bit is treated as any other number
• Ignore any carry on the leftmost position
• Subtraction
• Treat the numbers as unsigned integers
• If a "borrow" is necessary in the leftmost place,
  borrow as if there were another invisible
  one-bit to the left of the minuend

90
Ones Complement

• Devised to make the addition of two numbers with
  different signs the same as two numbers with the
  same sign
• Positive numbers are represented in the usual way
• For negatives
• STEP 1 Start with the binary representation of
  the absolute value
• STEP 2 Complement all of its bits

91
One's Complement Operations

• Treat the sign bit as any other bit
• For addition, carry out of the leftmost bit is
  added to the rightmost bit end-around carry

92
Introduction to C
93
C Usages Conventions

• C is absolutely case sensitive
• For Instance A is 97 in ASCII and a is 65
• Remember in ASCII , , and ( are not equivalent
• No keywords in ANSI standard are even partially
  uppercase
• While is not a keyword, while is
• Be careful if you define new keywords
• The most common practice in C is to use small
  letters of the first part of a variable name and
  capitals for the rest of it

94
Characteristics of a C Program

• Comments
• Compiler Directives
• Functions
• Braces
• Statements

95
A Simple C Program

• Comments //Simple C Program
• //
• // Purpose To demonstrate the
• // parts of a simple C program
• Compiler Directive include ltiostream.hgt
• Main Function main ( )
• Braces
• Statements cout ltlt "This is a simple program
  "
• return 0

96
Comments

• Document what is happening, why it is happening
  and other issues
• Commentary is ignored by the compiler
• C has inline, block and documentary comments
• Inline comments are within line of code
• Use the // symbols
• Block comments are long comments delimited with
  / and /

97
Compiler Directives

• Instructions to the compiler rather than part of
  the C language
• Most common directive is include
• For Example include ltiostream.hgt
• A .h file is a header file. It serves as a link
  between program code and standard C code needed
  to make programs run

98
Functions

• A function is a block of code that carries out a
  specific task
• Every C program has a main function that
  executes when a program initiates
• Includes open parenthesis to designate a function
• Ends with a return 0 statement

99
Scope Delimiters

• A symbol or pair of symbols used to define a
  region or area which is considered a locale
• In programming, many structures need to have
  their scope defined because they should not
  affect the entire program
• In C, the symbols and are used

100
Semicolons

• There must be a semicolon after every statement
• To tell the compiler that the statement is
  complete
• Function definitions and compiler directives are
  exempt

101
Columns and White Space

• Modern programming languages are free form with
  delimiters instead of columns to determine the
  end of instructions
• The (semi-colon) is the delimiter used in C
• Use tabs, indents, and blank lines in any manner
  that makes code easier to understand
• Many programming instructions become subordinate
  to other instructions due to scope and other
  restrictions. Formatting code to reflect this
  makes it easier to read

102
Uppercase or Lowercase

• Be careful to use the same combination of
  uppercase or lowercase lettering when you enter
  source code
• Commands and other reserved words are all lower
  case

103
Variables

• Variables or identifiers are used to hold
  information
• Usually mixed case with the first letters small
  and the rest starting with a capital
• e.g. theWeight

104
Literals

• Literals are system commands and other pieces of
  information that the compiler doesnt understand,
  and therefore, takes your word for them
• In C, literals are enclosed in straight double
  quotes " " which is the shift of the apostrophe

105
C Control Structures

• "Sequence statements" are imperatives
• "Selection" is the "if then else" statement
• AND, OR, NOT and parentheses ( ) can be used for
  compound conditions
• "Iteration" is satisfied by a number of
  statements
• "while"
• " do "
• "for"
• The case-type statement is satisfied by the
  "switch" statement.
• CASE statements are used for most non-trivial
  selection decisions

106
Variables

• Used to store values in virtually every computer
  program
• Used for remembering things during program
  execution
• Variables have names, types and values
• Values can change during execution

107
Data Types - Whole Numbers

• To store whole numbers in a variable, we use a
  variable of the int data type.
• An int variable uses 4 bytes of memory.
• An int variable can store a number as low as
  -2,147,483,648.
• An int variable can store a number as high as
  2,147,483,647.

108
Data Types - Decimal Numbers

• To store decimal numbers in a variable, we use a
  variable of the double data type
• A double variable uses 8 bytes of memory
• A double variable can store a number as low as
  -1.7 x 10308
• A double variable can store a number as high as
  1.7 x 10308
• A double variable can store a number with up to
  15 digits of precision (significant digits)

109
Data Types - Characters

• To store a letter or a single character (such as
  , , , etc.), we use a variable of the char
  data type.
• A char variable only uses 1 byte of memory.
• A char variable can only hold one letter, digit,
  or character.

110
Data Types Words / Phrases

• To store a word or phrase (string value), we use
  a variable that is a string
• Technically string is not a data type
• You can think of it as a data type for now

111
Using Variables in C

• Variables must be declared before they are used
  in C. Get into the habit of doing this at the
  top of your functions
• char grade // a students semester
  grade
• int numStudents // number of students in our
  class
• double price // price of item
• string userName // user's name

112
Variable Names

• Variable names are technically known as
  identifiers
• Choose your own variable names but you must be
  careful to use valid ones. Otherwise, the
  compiler will be confused and errors will result.
  When choosing your variable names
• do not use keywords that are defined in the
  programming language (Reserved Words)
• do not include spaces or other disallowed
  characters
• do not use more than 31 characters
• do begin the identifier with a letter
• Remember, C is completely case sensitive

113
Initializing Variables

• C does not automatically initialize all
  variables to the value 0
• If you do not initialize a variable to a certain
  value, the variable will have an indeterminate
  value that can corrupt the logic of your program
• You should usually initialize your variables at
  the same time that you declare them. This is done
  with a declaration statement that is also an
  initialization statement
• int numberOfPizzas 3          double
  monthlyCarPayment 685char letterGrade
  'A'string firstName "Paul"

114
Constants

• Sometimes you need to use the same value many
  times throughout a program. In this case, it is
  proper to use a constant rather than a variable
• Constants allow you to give a name to a value
  used several times in a program
• The value never changes

115
Type Compatibilities

• You cannot store a value of one type in a
  variable of a different type a type mismatch
  occurs
• You can typecast
• Supply the name of the data type you want to use
  to interpret the variable followed by the
  variable placed in parenthesis
• C PI float (diameter)

116
The Assignment Operator

• The assignment operator is the equal symbol ()
• The assignment operator changes the value of the
  variable to its left after evaluating the
  expression on its right
• For example
• sum 3 1000
• The variable sum ends up with the value 1003
• salary 40000
• poundsPressure 15 12
• sum original 300
• salary salary raise

117
Multiple Assignments

• i j k 10
• // initializes all three variables to the value,
  10
• This statement is equivalent to
• i 10
• j 10
• k 10

118
Common Arithmetic Operators

• for addition
• - for subtraction
• for multiplication
• / for division
• for modulus (like finding the remainder
  of a division problem)

119
Compound Operators

• Example 1
• j 1
• // is the same as j j 1
• Example 2
• total / 2
• // is the same as total total / 2

120
Increments and Decrement

• The incrementing () and decrementing (--)
  operators are useful at times if used carefully
• counter
• is equivalent to counter counter 1
  and counter 1
• counter--
• is equivalent to counter counter - 1
  and counter - 1
• Use the incrementing and decrementing operators
  with variables in statements such as these, that
  is with no other operators or code except the
  variable name that is being incremented or
  decremented.

121
Order of Operations

• Obey the order of operations
• Perform the following mathematical operations in
  this order Parentheses, Exponentiation,
  Multiplication, Division, Addition and
  Subtraction
• Multiplication and division are of equal
  precedence, so you must work left to right within
  an algebraic expression
• The modulus operator () has the same precedence
  as and / but is higher in precedence than and
  -.
• Addition and subtraction work left to right
  within an algebraic expression as well
• Use parentheses if necessary to override the
  order of operations in order to produce the
  desired result

122
Decision Making In Computers

• A circuit quite simply allows one out of two
  choices to be made depending on its inputs
• When decisions are made in a computer program,
  they are simply the result of a computation in
  which the final result is either TRUE or FALSE
• The value zero (0) is considered to be FALSE by
  C. Any positive or negative value is considered
  to be TRUE

123
Using Relational Operators

• Relational operators provide the tools with
  which programs make decisions with true and false
  evaluations

equal to NOTE this is two equals
symbols next to each other, not to be confused
with the assignment operator, gt greater
thanlt less thangt greater than or
equal tolt less than or equal to!
not equal to
124
Order of Logical Operations

• Logical operators may be mixed within evaluation
  statements but the following order of preference
  must be respected
• NOT operator (!)
• AND operator ()
• OR operator ()
• Short-circuit evaluation in C allows the
  compiler to quickly evaluate a logical expression
  in some cases without having to completely
  evaluate each part of the expression

125
Complete order of operations

• The complete order of operations including all of
  the arithmetic, relational, and logical operators
  including all of the basic arithmetic,
  relational, logical operators is
• , /,
• , -
• lt, gt, lt, gt, , !
• !

126
Color Coding in Visual C Editor

• Comments are green and are ignored by the
  compiler
• All ANSI keywords are coded in blue
• Other code is in plain black
• Compiler keywords like cin and cout are also
  shown in black

127
C2065 Undeclared Identifier

• Several things may produce this error
• Misspelling a keyword
• Misspelling a programmer defined name
  (identifier)
• Misuse of case in a keyword or identifier
• Failure to declare an identifier