CPS120 Introduction to Computer Science

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CPS120 Introduction to Computer Science

• Final Exam Review

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Common Flowchart Symbols
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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

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Compiling and Debugging

• Executable code will not be created until you
  correct all of the syntax errors in your source
  code

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Introduction to C
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Variable Names

• Choose your own variable names but you must be
  careful to use valid ones
• 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 255 characters
• do begin the identifier with a letter

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Declaring Initializing Variables

• In C all variables must be declared before they
  can be used.
• Declare a variable by indicating its type and
  name
• int myVariable
• C does not automatically initialize all
  variables to the value 0
• If you do not initialize a variable, the variable
  will have an indeterminate value.
• Initialize your variables at the same time that
  you declare them.
• int myVariable 0

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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

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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

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Common Arithmetic Operators

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

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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.

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Using Relational Operators

• Relational operators provide the tools with
  which programs make decisions

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
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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 ()

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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, , !
• !

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String Literals

• A string literal is a sequence of characters that
  is used in a C program between double quotes
  such as in the statementcout ltlt "Hello
  world!"where "Hello world!" is the string
  literal
• Similar to a constant
• Ends with an invisible null terminator (ASCII 0)
• Represented as \0

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Character Arrays

• Used to store strings that change as the program
  runs
• Unlike string literal
• An array is a group of variables of the same data
  type that appear together in memory
• In this case each variable holds a character and
  the last variable in the string holds the null
  terminator (/0)

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Using Strings In Programs

• In order to use string variables within any
  Cprogram, you must use the compiler directive
• include ltstring.hgt
• using namespace std

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Input Operations

• The operator gtgt is known as the input operator.
  It is also known as the extraction operator
• You use the input operator in statements like,
• cin gtgt numItems
• which would allow the user to input a value to
  be stored in the variable numItems.

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Decision Making in C

1. if statement
2. switch statement
3. ? conditional operator statement
4. goto statement

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IF-THEN
Test condition p
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IFELSE
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General Form

• if (test expression)
• True-block statements
• else
• False-block statements
• next statement

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Switch Structure

• The switch structure is a multiple-selection
  structure that allows even more complicated
  decision statements than a two-way if/else
  structure allows.
• Only variables with the INT or CHAR data types
  may be used in the control expressions (i.e.
  parentheses) of switch statements.
• Single quotes must be used around CHAR variables
• Single quotes are NOT used around the integer
  values

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Iteration

• A program loop is a form of iteration. A computer
  can be instructed to repeat instructions under
  certain conditions.

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Syntax of a for Loop

• for (initializing expression control expression
  step expression) // one or more
  statements
• The initializing expression sets the counter
  variable for the loop to its initial value.
• The control expression ends the loop at the
  specified moment.
• The step expression changes the counter variable
• Semi-colons, not commas, divide the expressions

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WHILE Loop
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While Loop Syntax

• while (control expression) // one or
  more statements
• The control expression must evaluate to TRUE in
  order for the while loop to iterate even once

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DO WHILE Loop
Loop statement a
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Do While Syntax

• do // body statements would be placed
  herewhile (control expression)
• Don't forget to include the required semicolon
  after the control expression

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In Summary

• Loops
• for -- fixed number of loops
• while -- may never be run
• do while -- always run once
• continue causes while, do while, and for loops
  to start over
• break causes while, do while, for and switch
  statements to end

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An Example of A Function

• include ltiostream.hgt
• void printMyMessage(int numOfTimes) //
  PROTOTYPE and NAME
• int main( )
• int userInput 0
• cout ltlt "Enter a number between 1 and 10 (0 to
  Exit) "
• cin gtgt userInput
• if (userInput ! 0)
• printMyMessage (userInput) // CALL
  STATEMENT WITH ACTUAL PARAMETER
• else
• cout ltlt "Thanks, Bye!"
• return 0
• // end of main
• void printMyMessage(int numOfTimes) // FUNCTION
  HEADER W/ RETURN TYPE ACTUAL PARAMETER

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Scope of Variables

• The scope of a variable is the area in which it
  can be legally referenced
• Variables are either global or local in nature
• Global variables can be used in any function
  throughout the program.
• Local variables are ones that are declared inside
  of a function, including main. They cannot be
  used or referred to in other functions
• It is not wise to use global variables any more
  than you have to

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Required Compiler Directives

• Any program that uses file pointers must include
  the fstream.h header file with the compiler
  directive,include ltfstream.hgtat the top of
  the program

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Opening Output Files

• Opening a sequential-access file
• ofstream outfile
• ofstream is a C keyword indicating the type of
  pointer that you created
• outfile is simply the programmer's chosen name
  for the file pointer (and can be any valid name)
• Open the file "mydata.txt" that is stored on your
  PC's hard drive
• outfile.open("mydata.txt", iosout)

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Opening Input Files

• Declare a file pointer as an ifstream object
  with
• ifstream infile
• ifstream is a keyword and infile is the name for
  the file pointer.
• infile is simply the programmer's chosen name for
  the file pointer (and can be any valid name)
• Open the actual file for reading with
• infile.open("mydata.txt", iosin)

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Writing Output

• To write data to a sequential-access data file
  you would use a statement like
• outfile ltlt "John Doe" ltlt endl
• to print that name to the next line in the data
  file pointed to by the file pointer, outfile.

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Appending Data

• Adding data to the end of a sequential-access
  data file is called appending
• Open the file using the iosapp stream operation
  mode as in
• outfile.open("myfile.txt", iosapp)
• where the app is short for append.

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Detecting the End of a File.

• Use the eof function to determine whether the end
  of a sequential-access file has been reached.
• This function returns a 1 (true) if an attempt
  has been made to read past the end of the file.
• do
• infile gtgt x
• if ( !infile.eof( ) )
• cout ltlt x ltlt endl
• while ( !infile.eof( ) )

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Arrays A Definition

• A list of variables accessed using a single
  identifier
• May be of any data type
• Can be single or multi-dimensioned
• Vector classifications are object-oriented
  representations of arrays

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Declaring an Array

• To declare an array before it is used in the body
  of your program, you must use a statement like
• int scores10
• In this case, scores can store up to 10 different
  integer values.
• The positions of the array are identified by
  their index positions which run from 0 to 9 (not
  1 to 10.)
• Each one of the 10 variables in scores is called
  an element

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Initializing an Array

• If you wish to initialize each element of an
  array to a specific value, you can use the
  statement,int scores 65, 76, 45, 83, 99
• You don't even have to specify a size of the
  array in this case since the initialization
  statementwould cause the compiler to declare an
  array of size 5 since there are five values in
  the set of curly braces

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Declaring a Multi-dimensional Array

• To declare an array of integers called
  studentGrades to be a 2-dimensional array with 3
  rows and 4 columns, you would use the
  statementint studentGrades3 4where the
  first integer value is used to specify the number
  of rows in the array and the second value
  specifies the number of columns
• Think of remote control

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Initializing a Multi-dimensional Array

• You can initialize the 2-dimensional array when
  you declare it by using commas and braces
  appropriately
• int studentGrades3 4
• 1, 2, 3, 4,
• 5, 6, 7, 8,
• 9, 10, 11, 12

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Key Computing Concepts
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What Is a Network

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

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Small Networks

• 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

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The Networking Revolution

• Computer networks have permanently altered the
  world of computing with the client/server model

Client/Server interaction
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Types of Networks
Various network topologies

• A bus technology called Ethernet has become the
  industry standard for local-area networks

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Ethernet

• A bus technology called Ethernet has become the
  industry standard for local-area networks
• Most popular and least expensive solution
• Each computer waits for a pause before sending
  information
• Collisions between information often occur
• Computers wait a moment, then resend

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Packet Switching

• To improve the efficiency of transferring
  information over a shared communication line,
  messages are divided into fixed-sized, numbered
  packets
• Network devices called routers are used to direct
  packets between networks

Messages sent by packet switching
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TCP/IP

• TCP stands for Transmission Control Protocol
• TCP software breaks messages into packets, hands
  them off to the IP software for delivery, and
  then orders and reassembles the packets at their
  destination
• IP stands for Internet Protocol
• IP software deals with the routing of packets
  through the maze of interconnected networks to
  their final destination

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Firewalls

• A firewall is a machine and its software that
  serve as a special gateway to a network,
  protecting it from inappropriate access
• Filters the network traffic that comes in,
  checking the validity of the messages as much as
  possible and perhaps denying some messages
  altogether
• Enforces an organizations access control policy

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Network Addresses

• An IP address can be split into
• network address, which specifies a specific
  network
• host number, which specifies a particular machine
  in that network

An IP address is stored in four bytes
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Domain Name System

• A hostname consists of the computer name followed
  by the domain name
• orchard.wccnet.org is the domain name
• A domain name is separated into two or more
  sections that specify the organization, and
  possibly a subset of an organization, of which
  the computer is a part
• Two organizations can have a computer named the
  same thing because the domain name makes it clear
  which one is being referred to

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Other Programming Concepts
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Approaches to Sorting

• There are two basic approaches to sorting data
• The incremental approach
• The divide and conquer approach.
• Using the incremental approach, one sorts the
  whole list at once
• The divide and conquer approach splits the list
  up into parts and sorts each part separately.

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Selection Sort
Example of a selection sort (sorted elements are
shaded)
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The Insertion Sort

• The insertion sort is incremental in nature.
• This is similar to the way a person usually
  organizes a hand of playing cards.
• The insertion sort is relatively quick for small
  lists that are close to being sorted

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Insertion Sorting
Mary Mary Gerri
Terry Gerri Kari
Gerri Kari Harry
Kari Harry Barry
Harry Barry Mary
Barry Terry Terry
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Bubble Sort

• Starting with the last list element, we compare
  successive pairs of elements, swapping whenever
  the bottom element of the pair is smaller than
  the one above it

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Bubble Sort
Example of a bubble sort
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Understanding the Quick Sort

• The quicksort is a divide and conquer algorithm
  and is more efficient than incremental sorts. It
  can be difficult to code though since it uses
  recursion or stacks.
• The original list is partitioned into two lists.
• One of the lists contains elements that are
  greater than the first original element.
• The second list contains elements that are less
  than or equal to the first original element.

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Quicksort
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Sequential Searching

• Although there are more efficient ways to search
  for data, sequential searching is a good choice
  of methods when amount of data to be searched is
  small.
• You simply check each element of an array
  position by position until you find the one that
  you are looking for.
• In any search, the item upon which the search is
  based is called the key and the field being
  searched is called the key field.

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Binary Search

• A binary search looks for an item in a list using
  a divide-and-conquer strategy
• Binary search algorithm assumes that the items in
  the list being searched are sorted
• The algorithm begins at the middle of the list in
  a binary search
• If the item for which we are searching is less
  than the item in the middle, we know that the
  item wont be in the second half of the list
• Once again we examine the middle element (which
  is really the item 25 of the way into the list)
• The process continues with each comparison
  cutting in half the portion of the list where the
  item might be

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Binary Search

• 0 Ant
• 1 Cat
• 2 Chicken
• 3 Cow
• 4 Deer
• 5 Dog
• 6 Fish
• 7 Goat
• 8 Horse
• 9 Monkey
• 10 Snake

Trace of the binary search
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Object-Oriented Programming
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Object-Oriented Paradigm

• Data should be placed inside the objects and that
  these objects should communicate with each other
  in the form of messages

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Thinking Object-Oriented

• Think in an object-oriented way
• E.g. an answering machine encapsulates the
  functions of an answering machine with the data
  (messages).
• The buttons are the equivalent of sending
  messages to the machine

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Encapsulation

• Encapsulation is a language feature that enforces
  information hiding
• Both data and methods are contained within an
  object

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Inheritance

• Inheritance fosters reuse by allowing an
  application to take an already-tested class and
  derive a class from it that inherits the
  properties the application needs

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Polymorphism

• Polymorphism the ability of a language to have
  duplicate method names in an inheritance
  hierarchy and to apply the method that is
  appropriate for the object to which the method is
  applied

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Designing A Class

• A class is a language construct that is a pattern
  for an object and provides a mechanism for
  encapsulating the properties and actions of the
  object class
• We instantiate the class
• Private and public are called access modifiers

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OOP Advantages Reusability

• Reusability is a major benefit of object-oriented
  programming

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Public vs. Private

• Private Cannot be accessed outside the object
• Public Can have access to all the variables and
  functions
• public
• // constructors
• circle() // default
  constructor
• circle(const circle ) // copy constructor
• // member functions
• void SetRadius(float)
• double Area()
• private
• // data
• float radius