C %20Data%20Types%20and%20Data%20Abstractions

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CData Types and Data Abstractions
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C Data Types

• Namespaces
• Built-in data types
• Literal constants
• Variables
• Pointers
• References
• The C string Type
• The const Qualifier

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What is using namespace std

• include ltiostreamgt
• using namespace std
• void main ( )
• int start 5
• int end 19
• if (start lt end )
• cout ltlt A
• // end if
• cout ltlt B
• // end main

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Namespaces

• The problem When two variables (or functions) in
  global scope have the same identifier (name), we
  get a compile-time error.
• To avoid such name collisions, programmers need
  to use unique identifiers in their own code.
• In C, if you use multiple third-party libraries
  and there is a name collision, you have three
  choices
• Get the source code to the libraries and modify
  and recompile it,
• ask one of the library publishers to rename
  their identifiers, or
• decide not to use one of the libraries.
• Often, none of these options are available.

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Namespaces

• To tackle this problem, C introduced
  namespaces.
• All identifiers declared within a defined block
  are associated with the blocks namespace
  identifier.
• All references to these identifiers from outside
  the block must indicate the namespace identifier.
• One example is the namespace std, in which
  Standard C defines its librarys identifiers,
  such as the cout stream object.

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Namespaces

• You can access objects in the namespace std in
  the following way using the scope resolution
  operator
• include ltiostreamgt
• int main()
• stdcout ltlt Hello World!
• return 0

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Namespaces

• Or, you can use the using namespace statement to
  omit the corresponding namespace references
• include ltiostreamgt
• using namespace std
• int main()
• cout ltlt Hello World!
• return 0

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Namespaces

• This is how you define your own namespaces
• include ltiostreamgt
• namespace MyNames
• int value1 10
• int value2 20
• int ComputeSum()
• return (value1 value2)
• int main()
• stdcout ltlt MyNamesComputeSum() ltlt stdendl

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Namespaces

• If you use multiple using namespace statements,
  you may get a compile-time error due to
  ambiguity
• include ltiostreamgt
• namespace MyNames
• int value1 10
• int value2 20
• namespace MyOtherNames
• int value1 30
• int value2 40

using namespace std using namespace
MyNames using namespace MyOtherNames int
main() value1 50
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Namespaces

• You can also define nested namespaces
• include ltiostreamgt
• namespace MyNames
• int value1 10
• int value2 20
• namespace MyInnerNames
• int value3 30
• int main()
• stdcout ltlt MyNamesvalue1 ltlt stdendl
• stdcout ltlt MyNamesMyInnerNamesvalue3 ltlt
  stdendl

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Numeric Data Types

• Type char represents individual characters and
  small integers (1 byte).
• Types short, int, and long represent integer
  values (half a machine word, 1 machine word, 1 or
  more machine words)
• Types float, double, and long double represent
  floating point values (1 machine word, 2 machine
  words, 3 or 4 machine words)

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Numeric Data Types

• Type char, short, int, and long are also called
  integral types.
• Integral types can be signed or unsigned.
• Example The value of an 8-bit unsigned char
  ranges from 0 to 255, while the range for an
  8-bit signed char is from 128 to 127.

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Literal Constants

• Literal constants are values that occur in a
  program.
• Example
• int main()
• int students 21
• double pi 3.1416
• Here, 21 is a literal constant of type int, and
  3.1416 is a literal constant of type double.

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Literal Constants

• We can use prefixes to write literal integer
  constants in decimal, octal, or hexadecimal
  notation.
• Examples Decimal (no prefix) 15

Octal (prefix 0 zero) 015
13 (decimal)
Hexadecimal (prefix 0x zero-x) 0x15
21 (decimal)
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Literal Constants

• By default, the C compiler assumes that all
  literal integer constants are of type int and all
  literal floating point constants are of type
  double.
• You can specify different types by appending a
  letter to the literal integer constant.
• Examples
• 2344U (unsigned)
• 1555L (long)
• 166UL (unsigned long)
• 3.1416F (float)
• 6.2831L (long double)

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Literal Constants

• Another built-in (or primitive) C data type is
  the type bool.
• Its only literals are true and false.
• Note that the type bool does not exist in C.
• In C, we represent the Boolean values true and
  false by the integers 1 and 0.

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Literal Constants

• We use single quotation marks to write literal
  character constants.
• Examples x, 4, , (space)
• Nonprintable characters and some special
  characters can be represented by escape
  sequences.
• Examples
• \n (newline), \a (bell), \t (tab)
• \\ (backslash), \ (single quote), \
  (double quote)

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Literal Constants

• Generalized escape sequences are indicated by a
  backslash followed by up to three digits.
• The value of the digits in the sequence is
  interpreted as the corresponding literal constant
  in the ASCII character set.
• Examples
• \7 (bell)
• \14 (newline)
• \65 (5)

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Literal Constants

• A character literal can be preceded by an L, for
  example La
• This is called a wide-character literal and has
  type wchar_t.
• Such wide-character literals support language
  character sets like Chinese and Japanese, which
  cannot be represented within the 256 character
  ASCII set.

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Literal Constants

• A literal string constant is composed of zero or
  more characters enclosed in double quotation
  marks.
• Examples
• (null string)
• x
• hello
• Hi,\nHow are you?\n

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Literal Constants

• A string literal can be written across multiple
  lines. You can use a backslash as the last
  character on a line to indicate that the string
  continues on the next line.
• Example
• This is an \
• excellent \
• multi-line string literal.

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Variables

• Variables provide us with named memory storage
  that we can
• write to,
• read from, and
• manipulate
• throughout the course of our program.
• Each variable has a specific type, which
  determines
• the size and layout of its associated memory,
• the range of values that can be stored, and
• the set of operations that can be applied to
  it.
• Variables are also referred to as objects.

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Variables

• There are two values associated with a variable
• Its data value, which is stored at some memory
  address. It is also called the rvalue (read
  value) of the variable.
• Its address value, indicating the location in
  memory where its data value is stored. This
  value is also referred to as the variables
  lvalue (location value).

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Pointers

• A pointer holds the memory address of another
  object.
• Through the pointer we can indirectly manipulate
  the referenced object.
• Pointers are useful for
• Creating linked data structures such as trees and
  lists,
• management of dynamically allocated objects, and
• as a function parameter type for passing large
  objects such as arrays.

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Pointers

• Every pointer has an associated type.
• The type of a pointer tells the compiler how to
  interpret the memory content at the referenced
  location and how many bytes this interpretation
  includes.
• Examples of pointer definitions
• int pointer
• int pointer1, pointer2
• string myString

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Pointers

• The dereference operator () dereferences a
  pointer variable so that we can manipulate the
  memory content at the location specified by the
  pointer.
• The address-of operator () provides the memory
  address (a pointer) of a given object.

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Pointers

• Example Correct or incorrect?
• int var1333, var2444, pvar1, pvar2

pvar1 var1
incorrect. int ? int
pvar2 var2
correct. int int
pvar1 var2
correct. int int
pvar2 pvar1 100
correct. int int
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Pointers

• Notice that in pointer definitions the symbol
  indicates the pointer type and is not the
  dereference operator.
• Example
• int var
• int pvar1 var
• Incorrect! During initialization a pointer can
  only be assigned an address
• int var
• int pvar1 var
• Correct!

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References

• References (aliases) can be used as alternative
  names for objects.
• In most cases they are used as formal parameters
  to a function.
• A reference type is defined by following the type
  specifier with the address-of operator.
• Example
• int val1 333
• int refVal1 val1

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References

• A reference must be initialized.
• Once defined, a reference cannot be made to refer
  to another object.
• All operations on the reference are actually
  applied to the object to which the reference
  refers.
• Example
• int val1 333
• int refVal1 val1
• val1
• refVal1 100
• cout ltlt Result ltlt refVal1
• Result 434

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Pass-by-value
sends a copy of the contents of the actual
parameter
SO, the actual parameter cannot be changed by
the function.
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Pass-by-reference
can change value of actual parameter
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The C string Type

• To use the C string type, you must include its
  associated header file
• include ltstringgt
• Different ways to initialize strings
• string myString(Hello folks!)
• string myOtherString(myString)
• string myFinalString // empty string
• The length of a string is returned by its size()
  operation (without the terminating null
  character) cout ltlt myString.size()
• 12

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The C string Type

• We can use the empty() operation to find out
  whether a string is empty
• bool isStringEmpty myString.empty()
• Use the equality operator to check whether two
  strings are equal
• if (myString myOtherString)
• cout ltlt Wow, the strings are equal.
• Copy one string to another with the assignment
  operator myFinalString myOtherString

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The C string Type

• Use the plus operator to concatenate strings
• string s1 Wow! , s2 Ouch!
• const char s3 Yuck!
• s2 s1 s3 s2
• cout ltlt s2
• Ouch! Wow! Yuck! Ouch!

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The const Qualifier

• The const type qualifier transforms an object
  into a constant. Example const double pi
  3.1416
• Constants allow you to store parameters in
  well- defined places in your code
• Constants have an associated type.
• Constants must be initialized.
• Constants cannot be modified after their
  definition.
• Constants replace the define technique in C.

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The const Qualifier

• Sometimes you may want to define for your object
  a set of states or actions.
• For example, you could define the following
  states for the Student Counselor
• observeStudent
• shoutAtStudent
• followStudent
• rechargeBattery

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The const Qualifier

• Using the const qualifier, you could define the
  following constants
• const int observeStudent 1
• const int shoutAtStudent 2
• const int followStudent 3
• const int rechargeBattery 4
• A function SetRobotState could then be defined as
  follows
• bool SetRobotState(int newState)
• int currentState newState
• return executionSuccessful

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Enumeration Types

• However, mapping states onto integers has certain
  disadvantages
• You cannot restrain the range of values that
  are passed to SetRobotState.
• There is no useful typing if you define
  individual sets of states for multiple
  objects, each object could formally be set
  to any of these states, not only its
  individual ones.
• This problem can be solved with enumeration types.

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Enumeration Types

• Enumeration types can be defined as follows
• enum robotState observeStudent 1,
  shoutAtStudent,
• 
  followStudent,
• 
  rechargeBattery
• This way we defined a new type robotState that
  can only assume four different values.
• These values still correspond to integers. For
  example,
• cout ltlt followStudent
• gives you the output 3.

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Enumeration Types

• We are now able to restrain the values that are
  passed to SetRobotState to the four legal ones
• bool SetRobotState(robotState newState)
• robotState currentState newState
• return executionSuccessful
• Any attempt to call SetRobotState with an integer
  value or a value of a different enumeration type
  will cause an error at compile time.

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C Data Types
structured
simple
array struct union class
integral enum
char short int long bool
43
Structured Data Types

• Chapter 11

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C Data Types
structured
simple
Skipping for now
array struct union class
integral enum
char short int long bool
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Structured Data Type

• A structured data type is a type in which each
  value is a collection of component items.
• The entire collection has a single name each
  component can be accessed individually

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C Structured Type

• Often we have related information of various
  types that wed like to store together for
  convenient access under the same identifier, for
  example . . .

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thisAnimal

.id 2037581 .name
giant panda .genus
Ailuropoda .species melanoluka .count
ry China .age
18 .weight 234.6 .health
Good
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anotherAnimal

.id 5281003 .name
llama .genus Lama .species
peruana .country Peru .age
7 .weight 278.5 .health
Excellent
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struct AnimalType

• enum HealthType Poor, Fair, Good,
  Excellent
• struct AnimalType // declares a struct data
  type
• // does not allocate memory
• long id
• string name
• string genus
• string species
  struct members
• string country
  
• int age
• float weight
• HealthType health
• AnimalType thisAnimal // declare variables
  of AnimalType
• AnimalType anotherAnimal

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struct type Declaration

• SYNTAX
• struct TypeName
• MemberList
• MemberList SYNTAX
• DataType MemberName
• DataType MemberName
• .
• .
• .

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struct type Declaration

• The struct declaration names a type and names the
  members of the struct.
• It does not allocate memory for any variables of
  that type!
• You still need to declare your struct variables.

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struct type declarations

• If the struct type declaration precedes all
  functions it will be visible throughout the rest
  of the file. If it is placed within a function,
  only that function can use it.
• It is common to place struct type declarations
  with TypeNames in a (.h) header file and include
  that file.
• It is possible for members of different struct
  types to have the same identifiers. Also a
  non-struct variable may have the same identifier
  as a structure member.

53
Accessing struct Members

• Dot ( period ) is the member selection operator.
• After the struct type declaration, the various
  members can be used in your program only when
  they are preceded by a struct variable name and a
  dot.
• EXAMPLES
• thisAnimal.weight
• anotherAnimal.country

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Valid operations on a struct member depend only
on its type

• thisAnimal.age 18
• thisAnimal.id 2037581
• cin gtgt thisAnimal.weight
• getline ( cin, thisAnimal.species )
• thisAnimal.name giant panda
• thisAnimal.genus 0 toupper
  (thisAnimal.genus 0 )
• thisAnimal.age

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Aggregate Operation

• An Aggregate operation is an operation on a data
  structure as a whole, as opposed to an operation
  on an individual component of the data structure.

56
Aggregate struct Operations

• I/O, arithmetic, and comparisons of entire
  struct variables are NOT ALLOWED!
• Operations valid on an entire struct type
  variable
• assignment to another struct variable of same
  type,
• pass to a function as argument (by value or
  by reference),
• return as value of a function

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Examples of aggregate struct operations

• anotherAnimal thisAnimal // assignment
• WriteOut(thisAnimal) // value parameter
• ChangeWeightAndAge(thisAnimal) // reference
  parameter
• thisAnimal GetAnimalData( ) // return value
  of function

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• void WriteOut( / in / AnimalType
  thisAnimal)
• // Prints out values of all members of thisAnimal
• // Precondition all members of thisAnimal
  are assigned
• // Postcondition all members have been
  written out
• cout ltlt ID ltlt thisAnimal.id ltlt
  thisAnimal.name ltlt endl
• cout ltlt thisAnimal.genus ltlt
  thisAnimal.species ltlt endl
• cout ltlt thisAnimal.country ltlt endl
• cout ltlt thisAnimal.age ltlt years ltlt
  endl
• cout ltlt thisAnimal.weight ltlt lbs. ltlt
  endl
• cout ltlt General health

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Passing a struct Type by Reference

• void ChangeAge ( / inout / AnimalType
  thisAnimal )
• // Adds 1 to age
• // Precondition thisAnimal.age is assigned
  
• // Postcondition thisAnimal.age
  thisAnimal.age_at_entry 1
• thisAnimal.age

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• AnimalType GetAnimalData ( void )
• // Obtains all information about an animal from
  keyboard
• // Postcondition
• // Function value AnimalType members entered
  at kbd
• AnimalType thisAnimal
• char response
• do // have user enter all members until
  they are correct
• .
• .
• .
• while (response ! Y )
• return thisAnimal

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Hierarchical Structures

• The type of a struct member can be another struct
  type. This is called nested or hierarchical
  structures.
• Hierarchical structures are very useful when
  there is much detailed information in each
  record.
• FOR EXAMPLE . . .

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struct MachineRec

• Information about each machine in a shop
  contains
• an idNumber,
• a written description,
• the purchase date,
• the cost,
• and a history (including failure rate, number
  of days down, and date of last service).

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• struct DateType
• int month // Assume 1 . . 12
• int day // Assume 1 . . 31
• int year // Assume 1900 . . 2050
• struct StatisticsType
• float failRate
• DateType lastServiced // DateType is
  a struct type
• int downDays
• struct MachineRec
• int idNumber
• string description
• StatisticsType history //
  StatisticsType is a struct type
• DateType purchaseDate
• float cost

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struct type variable machine

5719 DRILLING
3 21 1995 8000.0
.02 1 25 1999 4
.month .day .year
.month .day .year
.failrate .lastServiced .downdays
.idNumber .description . history
.purchaseDate .cost
machine.history.lastServiced.year has value 1999
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C Data Types
structured
simple
array struct union class
integral enum
char short int long bool
66
Unions in C

• Definition
• A union is a struct that holds only one of its
  members at a time during program execution.
• For Example
• union WeightType
• long wtInOunces
• int wtInPounds only one at a time
• float wtInTons

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Using Unions

• union WeightType // declares a union type
• long wtInOunces
• int wtInPounds
• float wtInTons
• WeightType weight // declares a union
  variable
• weight.wtInTons 4.83
• // Weight in tons is no longer needed. Reuse the
  memory space.
• weight.wtInPounds 35

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Abstraction

• Abstraction is the separation of the essential
  qualities of an object from the details of how it
  works or is composed
• It focuses on what, not how
• It is necessary for managing large, complex
  software projects

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Control Abstraction

• Separates the logical properties of an action
  from its implementation
• .
• .
• .
• Search (list, item, length, where, found)
• .
• .
• .
• The function call depends on the functions
  specification (description), not its
  implementation (algorithm)

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Data Abstraction

• Separates the logical properties of a data type
  from its implementation

LOGICAL PROPERTIES IMPLEMENTATION
What are the possible values? How can this be
done in C? What operations will be
needed? How can data types be used?
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Data Type
set of values (domain)
allowable operations on those values
For example, data type int has
operations , -, , /, , gtgt, ltlt
domain -32768 . . . 32767
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Abstract Data Type (ADT)

• Is a programmer-defined type with a set of
• values and allowable operations for the type.
• Some ways to define a new C type are
• using typedef
• using struct
• using class

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Using typedef

• typedef int Boolean
• typedef char String20 21
• String20 message // variable declarations
• Boolean seniorCitizen

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Using struct

• typedef char String20 21
• struct EmployeeType // declares a struct
  data type
• long idNumber
• String20 name data
  members
• int hoursWorked
• int numDependents
• float hourlyWage
• EmployeeType mySelf // declares variable

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mySelf
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Abstract Data Type (ADT)

• An ADT is a data type whose properties
  (domain and operations) are specified (what)
  independently of any particular implementation
  (how)
• For example . . .

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ADT Specification Example

• TYPE
• TimeType
• DOMAIN
• Each TimeType value is a time in hours, minutes,
  and seconds.
• OPERATIONS
• Set the time
• Print the time
• Increment by one second
• Compare 2 times for equality
• Determine if one time is less than another

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Another ADT Specification

• TYPE
• ComplexNumberType
• DOMAIN
• Each value is an ordered pair of real numbers
  (a, b) representing a bi.
• OPERATIONS
• Initialize the complex number
• Write the complex number
• Add
• Subtract
• Multiply
• Divide
• Determine the absolute value of a complex number

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ADT Implementation means

• Choosing a specific data representation for
  the abstract data using data types that already
  exist (built-in or programmer-defined)
• Writing functions for each allowable
  operation

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Information Hiding

• Class implementation details are hidden from the
  clients view. This is called information
  hiding.
• Public functions of a class provide the interface
  between the client code and the class objects.

client code
abstraction barrier
specification
implementation
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Benefits of information hiding

• Data and details can be concealed from the client
  of the abstraction.
• Code can be changed without affecting the client
  because the specification and interface are
  unchanged.

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Several Possible Representations of TimeType

• 3 int variables
• 3 strings
• 3-element int array
• Actual choice of representation depends on
  time, space, and algorithms needed to implement
  operations

10 45 27
83
Some Possible Representationsof ComplexNumberType

• struct with 2 float members
• 2-element float array

-16.2 5.8 .real .imag
-16.2 5.8
84
C Data Types
structured
simple
array struct union class
integral enum
char short int long bool
85
class TimeType Specification

• // Specification File ( timetype.h )
• class TimeType // declares a class data type
• // does not allocate memory
• public // 5 public function members
• void Set ( int hours , int mins , int
  secs )
• void Increment ( )
• void Write ( ) const
• bool Equal ( TimeType otherTime )
  const
• bool LessThan ( TimeType otherTime )
  const
• private // 3 private data members
• int hrs
• int mins
• int secs

86
Use of C data Type class

• Facilitates re-use of C code for an ADT
• Software that uses the class is called a client
• Variables of the class type are called class
  objects or class instances
• Client code uses public member functions to
  handle its class objects

87
Using class

• A class is a programmer-defined type whose
  components (called class members) can be
  variables or functions.
• Class members are private by default. Compiler
  does not permit client code to access private
  class members.
• Class members declared public form the interface
  between the client and the class.
• In most classes, the private members contain
  data, and the public members are functions to
  manipulate that data.

88
Member functions categorized by task

• CONSTRUCTOR -- a member function that actually
  creates a new instance and initialized some or
  all of its data members
• ACCESS FUNCTION or OBSERVER -- a member function
  that can inspect (use but not modify) the data
  members of a class without changing their values.
  Such a function is declared with const following
  the parameter list in both the specification and
  the implementation files.

89
Client Code Using TimeType

• include timetype.h // includes
  specification of the class
• using namespace std
• int main ( )
• TimeType currentTime // declares 2
  objects of TimeType
• TimeType endTime
• bool done false
• currentTime.Set ( 5, 30, 0 )
• endTime.Set ( 18, 30, 0 )
• while ( ! done )
• . . .
• currentTime.Increment ( )
• if ( currentTime.Equal ( endTime ) )
• done true

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90
class type Declaration

• The class declaration creates a data type and
  names the members of the class.
• It does not allocate memory for any variables of
  that type!
• Client code still needs to declare class
  variables.

91
C Data Type class represents an ADT

• 2 kinds of class members data members and
  function members
• Class members are private by default
• Data members are generally private
• Function members are generally declared public
• Private class members can be accessed only by the
  class member functions (and friend functions),
  not by client code.

92
Aggregate class Operations

• Built-in operations valid on class objects are
• Member selection using dot ( . ) operator ,
• Assignment to another class variable using (
  ),
• Pass to a function as argument
• (by value or by reference),
• Return as value of a function
• Other operations can be defined as class member
  functions

93
2 separate files Generally Used for class Type

• // Specification File (
  timetype .h )
• // Specifies the data and function members.
• class TimeType
• public
• . . .
• private
• . . .
• // Implementation File ( timetype.cpp
  )
• // Implements the TimeType member functions.
  
• . . .

94
Implementation File for TimeType

• // Implementation File (
  timetype.cpp )
• // Implements the TimeType member functions.
  
• include timetype.h // also must appear
  in client code
• include ltiostreamgt
• . . .
• bool TimeType Equal ( / in / TimeType
  otherTime ) const
• // Postcondition
• // Function value true, if this time
  equals otherTime
• //
  false , otherwise
• return ( (hrs otherTime.hrs) (mins
  otherTime.mins)
• (secs otherTime.secs) )
• . . .

95
Member selection operator .

• When a client uses a public member function,
  the function call requires a dot preceded by the
  name of the object. You can think of the
  function call as being sent to this object.
• ofstream outFile
• outFile.open (a\\my.out)
• .
• .
• .
• outFile.close( )

class type
variable, object, instance
96
Familiar Class Instances and Function Members

• The member selection operator ( . ) selects
  either data members or function members
• Header files iostream and fstream declare the
  istream, ostream,and ifstream, ofstream I/O
  classes
• Both cin and cout are class objects and get and
  ignore are function members
• cin.get (someChar)
• cin.ignore (100, \n)
• The statements below, declare myInfile as an
  instance of class ifstream and invoke function
  member open
• ifstream myInfile
• myInfile.open ( A\\mydata.dat )

97
Scope Resolution Operator ( )

• C programs typically use several class types
• Different classes can have member functions with
  the same identifier, like Write( )
• Member selection operator is used to determine
  the class whose member function Write( ) is
  invoked
• currentTime .Write( ) // class TimeType
• numberZ .Write( ) // class ComplexNumberType
• In the implementation file, the scope resolution
  operator is used in the heading before the
  function members name to specify its class
• void TimeType Write ( ) const
• . . .

98

TimeType Class Instance Diagrams
currentTime endTime
Set
Set
Private data hrs mins secs
Private data hrs mins secs
Increment
Increment
18 30 0
17 58 2
Write
Write
LessThan
LessThan
Equal
Equal
99
Use of const with Member Functions

• When a member function does not modify the
  private data members, use const in both the
  function prototype (in specification file) and
  the heading of the function definition (in
  implementation file)

100
Example Using const with a Member Function

• void TimeType Write ( ) const
• // Postcondition Time has been output
  in form HHMMSS
• if ( hrs lt 10 )
• cout ltlt 0
• cout ltlt hrs ltlt
• if ( mins lt 10 )
• cout ltlt 0
• cout ltlt mins ltlt
• if ( secs lt 10 )
• cout ltlt 0
• cout ltlt secs

100
101
Class Constructors

• A class constructor is a member function whose
  purpose is to initialize the private data members
  of a class object
• The name of a constructor is always the name of
  the class, and there is no return type for the
  constructor
• A class may have several constructors with
  different parameter lists. A constructor with no
  parameters is the default constructor
• A constructor is implicitly invoked when a class
  object is declared--if there are parameters,
  their values are listed in parentheses in the
  declaration

102
Specification of TimeType Class Constructors

• class TimeType // timetype.h
• public // 7 function members
• void Set ( int hours , int minutes ,
  int seconds )
• void Increment ( )
• void Write ( ) const
• bool Equal ( TimeType otherTime )
  const
• bool LessThan ( TimeType otherTime )
  const
• TimeType ( int initHrs , int initMins ,
  int initSecs ) // constructor
• TimeType ( ) // default constructor
• private // 3 data members
• int hrs
• int mins
• int secs

102
103
Implementation of TimeType Default Constructor

• TimeType TimeType ( )
• // Default Constructor
• // Postcondition
• // hrs 0 mins 0 secs 0
• hrs 0
• mins 0
• secs 0

104
Implementation of Another TimeType Class
Constructor

• TimeType TimeType ( / in / int initHrs,
• / in / int initMins,
• / in / int initSecs )
• // Constructor
• // Precondition 0 lt initHrs lt 23 0
  lt initMins lt 59
• // 0 lt initSecs lt 59
• // Postcondition
• // hrs initHrs mins initMins secs
  initSecs
• hrs initHrs
• mins initMins
• secs initSecs

104
105
Automatic invocation of constructors occurs

• TimeType departureTime // default
  constructor invoked
• TimeType movieTime (19, 30, 0 ) //
  parameterized constructor
• departureTime movieTime

Set
Set
Private data hrs mins secs
Private data hrs mins secs
Increment
Increment
0 0 0
19 30 0
Write
Write
LessThan
LessThan
Equal
Equal
106
Separate Compilation and Linking of Files
specification file
implementation file
main program
include timetype.h
Compiler
Compiler
Linker
107
Avoiding Multiple Inclusion of Header Files

• Often several program files use the same header
  file containing typedef statements, constants, or
  class type declarations--but, it is a
  compile-time error to define the same identifier
  twice
• This preprocessor directive syntax is used to
  avoid the compilation error that would otherwise
  occur from multiple uses of include for the same
  header file
• ifndef Preprocessor_Identifier
• define Preprocessor_Identifier
• .
• .
• .
• endif

108
Example Using Preprocessor Directive ifndef

• // timetype .h FOR COMPILATION THE CLASS
  DECLARATION IN
• // Specification File FILE timetype.h WILL BE
  INCLUDED ONLY ONCE
• ifndef TIME_H
• define TIME_H // timetype .cpp //
  client.cpp
• // Implementation File //
  Appointment program
• class TimeType
• include timetype.h include
  timetype.h
• public
• . . . . . . int main ( void
  )
• private . . .
• . . .
• endif

109
The End

• Next Lecture
• More about classes.
• How to create and use them.