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Chapter 2Data Design and Implementation
1
Lecture 4
Data
• The representation of information in a manner suitable for communication or analysis by humans or machines
• Data are the nouns of the programming world: • The objects that are manipulated• The information that is processed
3
Data Abstraction
• Separation of a data type’s logical properties 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?
4
APPLICATION
0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 1
REPRESENTATION
Data Encapsulation
• is the separation of the representation of data from the applications that use the data at a logical level; • a programming language feature that enforces
information hiding
int y;
y = 25;
5
Encapsulated C++ Data Type int
Value range: INT_MIN . . INT_MAX
Operations: + prefix - prefix + infix - infix * infix / infix % infixRelational Operators infix
TYPE int
(inside)
Representation of
int
as 16 bits two’s complement
+
Implementation of Operations
6
Abstract Data Type (ADT)
• A data type whose properties (domain and operations) are specified independently of any particular implementation.
7
Collection ordered in different ways
8
Data from 3 different levels
9
• Application (or user) level: modeling real-life data in a specific context.
• Logical (or ADT) level: abstract view of the domain and operations. WHAT
• Implementation level: specific representation of the structure to hold the data items, and the coding for operations. HOW
Communication between the Application Level and Implementation Level
10
Viewing a library from 3 different levels
• Application (or user) level: Library of Congress, or Baltimore County Public Library.
• Logical (or ADT) level: domain is a collection of books; • operations include: check book out, check book in,
pay fine, reserve a book.
• Implementation level: representation of the structure to hold the “books”, and the coding for operations.
11
Composite Data Type
A composite data type is a type which
• stores a collection of individual data components under one variable name,
• and allows the individual data components to be accessed.
12
4 Basic Kinds of ADT Operations
• Constructor -- creates a new instance (object) of an ADT.
• Transformer -- changes the state of one or more of the data values of an instance.
• Observer -- allows us to observe the state of one or more of the data values without changing them.
• Iterator -- allows us to process all the components in a data structure sequentially.
13
Two Forms of Composite Data Types
Components are not organized with respect to one another.
The organization determines method used to access individual data components.
UNSTRUCTURED STRUCTURED
EXAMPLES: EXAMPLES: arraysclasses and structs
14
C++ Built-In Data Types
Composite
array struct union class
Address
pointer reference
Simple
Integral Floating
char short int long enum
float double long double
15
Records
A record is a composite data type made up of a finite collection of not necessarily homogeneous elements called members or fields.
For example . . .
.year 2008
.maker ‘h’‘o’‘n’‘d’ ‘a’‘\0’ . . .
.price 18678.92
thisCar at Base Address 6000
16
struct CarType
struct CarType{
int year; char maker[10]; float price;
} ;
CarType thisCar; //CarType variables
CarType myCar;
17
Accessing struct members
The member selection operator (period . ) is used between the variable name and the member identifier to access individual members of a record (struct or class) type variable.
EXAMPLES
myCar.year
thisCar.maker[4]
18
Valid struct operations
• Operations valid on an entire struct type variable:
assignment to another struct variable of same type,
pass as a parameter to a function
(either by value or by reference),
return as the value of a function.
19
Pass-by-value
CALLINGBLOCK
FUNCTION CALLED
sends a copy of the contents of the actual parameter
SO, the actual parameter cannot be changed by the function.
20
Pass-by-reference
sends the location (memory address)of the actual parameter
can change value ofactual parameter
CALLINGBLOCK FUNCTION
CALLED
21
Using struct type Reference Parameter to change a member
void AdjustForInflation(CarType& car, float perCent)
// Increases price by the amount specified in perCent{
car.price = car.price * perCent + car.price; };
SAMPLE CALL
AdjustForInflation(myCar, 0.03);
22
Using struct type Value Parameter to examine a member
bool LateModel(CarType car, int date)
// Returns true if the car’s model year is later than// or equal to date; returns false otherwise.{
return ( car.year >= date ) ;
};
SAMPLE CALL
if ( LateModel(myCar, 1995) )std::cout << myCar.price << std::endl;
23
One-Dimensional Array at the Logical Level
A one-dimensional array is a structured composite data type made up of
a finite,
fixed size (known at compile time)
collection of homogeneous (all of the same data type) elements
having relative positions and
to which there is direct access (any element can be accessed immediately).
Array operations (creation, storing a value, retrieving a value) are performed using a declaration and indexes.
24
Implementation Example
float values[5]; // assume element size is 4 bytes
This ACCESSING FUNCTION gives position of values[Index]
Address(Index) = BaseAddress + Index * SizeOfElement
Base Address
values[0] values[1] values[2] values[3] values[4]
7000 7004 7008 7012 7016
Indexes 25
One-Dimensional Arrays in C++
• The index must be of an integral type • char, short, int, long, or enum
• The index range is always 0 through the array size minus 1
• Arrays cannot be assigned one to another, • and cannot be the return type of a function
26
Another Example
char name[10]; // assume element size is 1 byte
name[0] name[1] name[2] name[3] name[4] . . . . . name[9]
6000 6001 6002 6003 6004 6005 6006 6007 6008 6009
Base Address
This ACCESSING FUNCTION gives position of name[Index]
Address(Index) = BaseAddress + Index * SizeOfElement
27
Passing Arrays as Parameters
• In C++, arrays are always passed by reference, • and & is not used with the formal
parameter type.
• Whenever an array is passed as a parameter, its base address is sent to the called function.
28
const array parameter
Because arrays are always passed as reference parameters, you can protect the actual parameter from unintentional changes by using const in formal parameter list and function prototype.
FOR EXAMPLE . . . // prototype
float SumValues( const float values[ ],
int numOfValues );
29
float SumValues (const float values[ ], numOfValues)
// Pre: values[ 0] through values[numOfValues-1]
// have been assigned
// Returns the sum of values[0] through
// values[numOfValues-1]
{
float sum = 0;
for ( int index = 0; index < numOfValues;
index++ )
{
sum = values [index] + sum;
}
return sum;
}
30
Two-Dimensional Array at the Logical Level
A two-dimensional array is a structured composite data type made up of a finite, fixed size collection of homogeneous elements having relative positions and to which there is direct access.
Array operations (creation, storing a value, retrieving a value) are performed using a declaration and a pair of indexes (called row and column) representing the component’s position in each dimension.
31
EXAMPLE -- To keep monthly high temperatures for 50 states in a two-dimensional array.
const int NUM_STATES = 50 ;const int NUM_MONTHS = 12 ;int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;
[ 0 ] [ 1 ] [ 2 ] . . stateHighs [2]
[7] . [ 48 ] [ 49 ]
[0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
66 64 72 78 85 90 99 115 98 90 88 80row 2,col 7might beArizona’shigh forAugust
32
Finding the average high temperature for Arizona
float total = 0;
int month;
float average;
for ( month = 0; month < NUM_MONTHS;
month ++ )
total = total + stateHighs [ 2 ][ month ];
average = ( total / NUM_MONTHS);
33
const int NUM_STATES = 50 ;const int NUM_MONTHS = 12 ;int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;
• In memory, C++ stores arrays in row order. The first row is followed by the second row, etc.
12 highs for state 0 12 highs for state 1 etc. Alabama Alaska first row second row
8000 8024 8048
Base Address
STORAGE
. . .
rows columns
34
Implementation Level View
stateHighs[ 0 ] [ 0 ]stateHighs[ 0 ] [ 1 ]stateHighs[ 0 ] [ 2 ]stateHighs[ 0 ] [ 3 ]stateHighs[ 0 ] [ 4 ]stateHighs[ 0 ] [ 5 ]stateHighs[ 0 ] [ 6 ]stateHighs[ 0 ] [ 7 ]stateHighs[ 0 ] [ 8 ]stateHighs[ 0 ] [ 9 ]stateHighs[ 0 ] [10 ]stateHighs[ 0 ] [11 ]stateHighs[ 1 ] [ 0 ]stateHighs[ 1 ] [ 1 ]stateHighs[ 1 ] [ 2 ]stateHighs[ 1 ] [ 3 ] . . .
To locate an element such asstateHighs [ 2 ] [ 7] the compiler needs to know that there are 12 columnsin this two-dimensional array.
At what address will stateHighs [ 2 ] [ 7 ] be found?
Assume 2 bytes for type int.
Base Address 8000
35
Example of a 2-dimensional object
36
Two-Dimensional Array Parameters
• Just as with a one-dimensional array, when a two- (or higher) dimensional array is passed as a parameter, the base address of the actual array is sent to the function.
• The size of all dimensions except the first must be included in the function heading and prototype.
• The sizes of those dimensions for the formal parameter must be exactly the same as in the actual array.
37
const int NUM_STATES = 50 ;const int NUM_MONTHS = 12 ;int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;float stateAverages [ NUM_STATES ] ;
[ 0 ] ? [ 1 ] ? [ 2 ] . . . [ 48 ] [ 49 ]
[0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
43 42 50 55 60 78 79 80 77 72 63 4066 64 72 78 85 90 99 115 98 90 88 80
Use the two-dimensional stateHighs array to fill a
one-dimensional stateAverages array
Alaska
Arizona
38
void findAverages (const int stateHighs [NUM_STATES] [NUM_MONTHS],
int stateAverages [NUM_STATES])
// Pre: stateHighs[ 0..NUM_STATES-1] [ 0..NUM_MONTHS-1] // assigned// Post: stateAverages[ 0..NUM_STATES-1 ] contains rounded // high temperature for each state{ int state; int month; float total; for ( state = 0 ; state < NUM_STATES; state++ ) { total = 0.0; for ( month = 0 ; month < NUM_MONTHS ; month++ )
total = stateHighs [ state ][ month ] + total; stateAverages [ state ] = total / NUM_MONTHS;
}}
39
Lecture 5
Using typedef with arrays
helps eliminate the chances of size mismatches between
formal and actual parameters.
FOR EXAMPLE,
typedef int StateHighsType [ NUM_STATES ][ NUM_MONTHS ];
typedef float StateAveragesType [ NUM_STATES ];
void findAverages( const StateHighsType stateHighs, StateAveragesType stateAverages )
{
.
.
.
}
41
Declaring Multidimensional Arrays
EXAMPLE USING TYPEDEF
const int NUM_DEPTS = 5;
// mens, womens, childrens, electronics, linens
const int NUM_MONTHS = 12 ;
const int NUM_STORES = 3 ;
// White Marsh, Owings Mills, Towson
typedef long MonthlySalesType [NUM_DEPTS] [NUM_MONTHS]
[NUM_STORES];
MonthlySalesType monthlySales;
42
43
const int NUM_DEPTS = 5; // mens, womens, childrens, electronics,linensconst int NUM_MONTHS = 12 ; const int NUM_STORES = 3 ; // White Marsh, Owings Mills, Towson
typedef long MonthlySalesType [NUM_DEPTS] [NUM_MONTHS] [NUM_STORES] ;MonthlySalesType monthlySales;
monthlySales[3][7][0]sales for electronics in August at White Marsh
12 MONTHS columns
5 D
EP
TS
ro
ws
3 STORES
sheets
43
C++ class data type
• A class is an unstructured type that encapsulates a fixed number of
data components (data members) with the functions (called member functions) that
manipulate them.
• The predefined operations on an instance of a class are whole assignment and component access.
44
class DateType Specification
// SPECIFICATION FILE ( datetype.h )
class DateType // declares a class data type{
public : // 4 public member functions
void Initialize (int newMonth, int newDay, int newYear ) ;int GetYear( ) const ; // returns yearint GetMonth( ) const ; // returns monthint GetDay( ) const ; // returns day
private : // 3 private data members
int year ; int month ; int day ;
}; ; must be there!!!
Use of C++ data type class
• Variables of a class type are called objects (or instances) of that particular class.
• Software that declares and uses objects of the class is called a client.
• Client code uses public member functions (called methods in OOP) to handle its class objects.
• . means calling a public member function.
46
Client Code Using DateType#include “datetype” // includes specification of the classusing namespace std;int main ( void ){ DateType startDate; // declares 2 objects of DateType DateType endDate; bool retired = false; startDate.Initialize ( 6, 30, 1998 ); endDate.Initialize ( 10, 31, 2002 ); cout << startDate.MonthIs( ) << “/” << startDate.DayIs( ) << “/” << startDate.YearIs( ) << endl; while ( ! retired ) { // finishSomeTask } }
47
// SPECIFICATION FILE ( datetype .h ) // Specifies the data and function members. class DateType { public: . . .
private: . . . } ;
// IMPLEMENTATION FILE ( datetype.cpp )
// Implements the DateType member functions. . . .
2 separate files generally used for class type
48
DateType Class Instance Diagrams
Initialize
GetYear
GetMonth
GetDay
startDate endDate
Private data:
year
month
day
2002
10
31
Initialize
GeytYear
GetMonth
GetDay
1998
6
30
Private data:
year
month
day
49
Implementation of DateType member functions
// IMPLEMENTATION FILE (datetype.cpp)
#include “datetype.h” // also must appear in client code
void DateType :: Initialize ( int newMonth,
int newDay,
int newYear )
// Post: year is set to newYear.
// month is set to newMonth.
// day is set to newDay.
{
year = newYear;
month = newMonth;
day = newDay;
}
50
51
int DateType :: GetMonth ( ) const// Accessor function for data member month{ return month;}
int DateType :: GetYear ( ) const// Accessor function for data member year{ return year;}
int DateType :: GetDay ( ) const// Accessor function for data member day{ return day;}
51
Familiar Class Instances and Member Functions
• The member selection operator ( . ) selects either data members or member functions.
• 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 member functions.
cin.get (someChar);cin.ignore (100, ‘\n’);
• These statements declare myInfile as an instance of class ifstream and invoke member function open.
ifstream myInfile ;myInfile.open ( “mydata.dat” );
52
Scope Resolution Operator ( :: )
• C++ programs typically use several class types.
• Different classes can have member functions with the same identifer, like Write( ).
• Member selection operator is used to determine the class whose member function Write( ) is invoked.
currentDate.Write( ) ; // class DateTypenumberZ.Write( ) ; // class ComplexNumberType
• In the implementation file, the scope resolution operator is used in the heading before the member function’s name to specify its class.
void DateType :: Write ( ) const{ . . .
} 53
Inheritance
54
A Short Review of Object-Oriented Programming
• Three inter-related constructs: classes, objects, and inheritance
• Objects are the basic run-time entities in an object-oriented system.
• A class defines the structure of its objects.
• Classes are organized in an “is-a” hierarchy defined by inheritance.
55
Inheritance
1. Allows programmers to create a new class that is a specialization of an existing class.
2. The new class is called a derived class of the existing class;
• the existing class is the base class of the new class.
56
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
• 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
57
Inheritance
• Inheritance and polymorphism combined allow the programmer to build useful hierarchies of classes that can be reused in different applications
• Mapping of problem into solution
58
# include <string>
class MoneyType
{
public:
void Initialize(long, long);
long DollarsAre( ) const;
long CentsAre( ) const;
private:
long dollars;
long cents;
};
59
class ExtMoneyType:public MoneyType{public: string CurrencyIs( ); void Initialize(long, long, const string);private: string currency;};ExtMoneyType extMoney;void ExtMoneyType::Initialize (long newDollars, long newCents, string newCurrency){ currency = newCurrency; MoneyType::Initialize(newDollars, newCents);}String ExtMoneyType::CurrencyIs() const{ return currency;
} 60
Exceptions
• An exception is an unusual situation that occurs when the program is running.
• Exception Management • Define the error condition• Enclose code containing possible error (try).• Alert the system if error occurs (throw).• Handle error if it is thrown (catch).
61
try, catch, and throw
Try{ // code that contains a possible error
… throw string(“An error has occurred in function …”);
}Catch (string message){
std::cout << message << std::endl;return 1;
}
62
try{ infile >> value; do { if (value < 0) throw string("Negative value"); sum = sum + value; } while (infile); } catch (string message) // Parameter of the catch is type string { // Code that handles the exception cout << message << " found in file. Program aborted." return 1; } // Code to continue processing if exception not thrown cout << "Sum of values on the file: " << sum;
Exits lo
op and goes
to catch
63
Namespace
namespace mySpace
{
// All variables and
// functions within this
// block must be accessed
// using scope
// resolution operator (::).
}
Purpose: Avoid namespace pollution.
64
Three Ways to Access Members within a Namespace
• Qualify each reference: mySpace::name with every reference.
• Using declaration: using mySpace::name;All future references to name refer to mySpace::name.
• Using directive:using namespace mySpace;All members of mySpace can be referenced without
qualification.
65
Rules for Use of Namespace std(within text)
• Qualify names in prototypes and/or function definitions.
• If name used more than once in a function block, use a using declaration.
• If more than one name is used from a namespace, use a using directive.
66
Lecture 6
constint const x = 5;const int x = 5;const int *p_int;int const *p_int;int * const p_int = &x;int const * const p_int = &x;
int method() const;const char * method();int method(int const *p_int);
68
x is a constant integer
a pointer to constant data
a constant pointer to data
a method that does not modify the object
a constant pointer to constant data
a method that has a constant output
a method whose parameter is constant
const int*const Method(const int*const&)const;
Map to Joe’s Diner
69
Which Cost More to Feed?
70
Order of Magnitude of a Function
The order of magnitude, or Big-O notation, of a function expresses the computing timeof a problem as the term in a function that increases most rapidly relative to the sizeof a problem.
71
Complexity
• Let us assume two algorithms A and B that solve the same class of problems.
• The time complexity of A is 5,000n, the one for B is 1.1n for an input with n elements.
• For n = 10, • A requires 50,000 steps, • but B only 3, • so B seems to be superior to A.
• For n = 1000, A requires 5,000,000 steps, • while B requires 2.51041 steps.
72
Complexity
• This means that algorithm B cannot be used for large inputs, while algorithm A is still feasible.
• So what is important is the growth of the complexity functions.
• The growth of time and space complexity with increasing input size n is a suitable measure for the comparison of algorithms.
73
Names of Orders of Magnitude
O(1) bounded (by a constant) time
O(log2N) logarithmic time
O(N) linear time
O(N*log2N) N*log2N time
O(N2) quadratic time
O(N3) cubic time
O(2N ) exponential time
74
N log2N N*log2N N2 2N
1 0 0 1 2
2 1 2 4 4
4 2 8 16 16
8 3 24 64 256
16 4 64 256 65,536
32 5 160 1024 4,294,967,296
64 6 384 4096 1.84*1019
128 7 896 16,384 3.40*1038
75
The Growth of Functions• “Popular” functions g(n) aren log n, log n, 1, 2n, n2, n!, n, n3
Listed from slowest to fastest growth:
• 1• log n• n• n log n• n2
• n3
• 2n
• n!
76
The Growth of Functions
• A problem that can be solved with polynomial worst-case complexity is called tractable
• Problems of higher complexity are called intractable
• Problems that no algorithm can solve are called unsolvable
77
Comparison of Two Algorithms
• Add all numbers from 1 to 20
78
Complexity Examples
What does the following algorithm compute?
int who_knows(int a[n]) {int m = 0;for {int i = 0; i<n; i++}
for {int j = i+1; j<n; j++}if ( abs(a[i] – a[j]) > m )
m = abs(a[i] – a[j]);return m;
}returns the maximum difference between any two numbers in the input arrayComparisons: n-1 + n-2 + n-3 + … + 1 = (n-1)n/2 = 0.5n2 - 0.5n
Time complexity is O(n2)
79
Complexity Examples
Another algorithm solving the same problem:
int max_diff(int a[n]) {int min = a[0];int max = a[0];for {int i = 1; i<n; i++}
if ( a[i] < min )min = a[i];
else if ( a[i] > max )max = a[i];
return max-min;}
Comparisons: 2n - 2
Time complexity is O(n).80
Find “John Smith”
81
Big-O Comparison of List Operations
OPERATION UnsortedList SortedList
GetItem O(N) O(N) linear search
O(log2N) binary search
PutItemFind O(1) O(log2N) searchPut O(1) O(N) moving downCombined O(1) O(N)
DeleteItemFind O(N) O(log2N) searchPut O(1) swap O(N) moving upCombined O(N) O(N)
82
OVERVIEW
Overview• The application view of a data structure is associated with which of the
following? • A. What? • B. Why? • C. How? • The implementation view of a data structure is associated with which of
the following? • A. What? • B. Why? • C. How? • The logical view of a data structure is associated with which of the
following? • A. What? • B. Why? • C. How?
84
OverviewThe file containing the definition of class DateType is called the ______ file.
A. specification
B. implementation
C.client
•The file containing the definitions of the member functions of class DateType is called the ______ file. •A. specification •B. implementation •C. client
85
Which of the following statements in a client program correctly prints out the day of the variable day1 of type DateType?
class DateType {
public:
void Initialize(int, int, int);
int GetYear() const; // returns year
int GetMonth() const; // returns month
int GetDay() const; // returns day
private:
int year;
int month;
int day;
};A. cout << day1.GetDay;
B. cout << day1.GetDay();
C. cout << GetDay.day1;
D. cout cout << GetDay(day1);
E. The day cannot be printed by a client program.
86
What is the minimum number of test cases needed to adequately test this program?
void CheckTriangle(int b, int c, int a)
{
if ((a == b) && (b == c))
cout << "Equalateral" << endl;
else
if (a == b)
cout << "Isoscelese" << endl;
else
cout << "Scalene" << endl;
}
687
True / False
• We can protect an array that is sent to a function by using const
• C++ ensures we do not write beyond allocated array slots.
• The position of an element in a one dimensional array associated with Index is Address(Index) = Base + Index * SizeOfElement
• In a two dimensional array, component selection is as follows
table[columnIndex][rowIndex]
88
True / False
• Members of a struct are public by default.
• Members of a class are public by default.
• A struct differs from an array in that its elements need not occupy a consecutive block of memory cells.
• C++ provides a way to sequentially iterate through the fields in a struct.
89
True / False
• Exceptions must be handled within the function in which they occur.
• Exceptions cannot be handled within the block in which they occur.
• Code that can cause an exception should be enclosed within a try clause.
• Exception handlers are enclosed within a catch clause.
• C++ does have built-in exceptions.
90
True / False
• Each try/catch statement can have only one catch clause.
• It is the responsibility of the client code to handle all exceptions.
• using myNames::GetData is a using declaration.
• using namespace myName is a using directive.
91
True / False
• Polymorphism has the ability to determine which function to call for a particular object.
• Inheritance is a language mechanism by which one class acquires data and operations of another class.
• Composition is a mechanism by which an internal data member of one class is defined to be an object of another class type.
92
is-a
has-a
True / False• Static binding refers to compile-time binding
• Dynamic binding refers to run-time binding
• In C++, a derived class's constructor is executed before the base class constructor is executed.
93