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SEN 909 OO Programming in C++SEN 909 OO Programming in C++Final ExamFinal Exam
Multiple choice, True/False and some minimal programming will be required
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Topics CoveredTopics Covered
• C++ basic programming concepts• Struct and Union Concepts• C++ Classes• Inheritance• Object-Oriented Programming• Pointers• You will have to write a class• You will have to write a struct
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Structured Data Type Structured Data Type
Definition: 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
Know what is meant by a structured data type. You do not need to create a struct or use one on the final exam.
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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.
EXAMPLESthisAnimal.weightanotherAnimal.country
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Abstraction 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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Abstract Data Type (ADT)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 struct
using class
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ADT Implementation means ADT Implementation means
Choosing a specific data representation for the abstract data using data types that already exist (built-in or programmer-defined) Called “Data Members”
Writing functions (member functions) for each allowable operation
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Information HidingInformation Hiding
Class implementation details are hidden from the client’s view. This is called information hiding.
Public functions of a class provide the interface between the client code and the class objects.
clientcode
specification implementation
abstraction barrier
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Benefits of information hidingBenefits 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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class TimeTypeclass TimeType Specification 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 ;
} ;
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Use of C++ data TypeUse of C++ data Type class 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
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Using Using classclass
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.
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Member functions categorized by taskMember 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.
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Client Code UsingClient Code Using TimeTypeTimeType
#include “timetype.h” // includes specification of the classusing 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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classclass type Declaration 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.
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C++ Data Type C++ Data Type classclass represents an ADT 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.
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AggregateAggregate class class Operations 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
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2 separate files Generally Used for2 separate files Generally Used for classclass Type Type
// Specification File ( timetype .h ) // Specifies the data and function members. class TimeType { public: . . .
private: . . . } ;
// Implementation File ( timetype.cpp ) // Implements the TimeType member functions. . . .
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Implementation File for Implementation File for TimeTypeTimeType
// Implementation File ( timetype.cpp ) // Implements the TimeType member functions.
#include “ timetype.h” // also must appear in client code #include <iostream>
. . .
bool TimeType :: Equal (TimeType otherTime ) const // Function value == true, if this time equals otherTime // == false , otherwise { return ( (hrs == otherTime.hrs) && (mins == otherTime.mins) && (secs == otherTime.secs)
) ; }
. . .
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Scope Resolution Operator ( :: ) 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 TimeTypenumberZ .Write( ) ; // class ComplexNumberType
In the implementation file, the scope resolution operator is used in the heading before the function member’s name to specify its class
void TimeType :: Write ( ) const{ . . .
}
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Class Constructors 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
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Specification of Specification of TimeType TimeType Class Class Constructors 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 membersint hrs ; int mins ; int secs ;
} ; 22
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Implementation of Implementation of TimeTypeTimeType Default Default Constructor Constructor
TimeType :: TimeType ( )// Default Constructor// Postcondition: // hrs == 0 && mins == 0 && secs == 0{
hrs = 0 ; mins = 0 ; secs = 0 ;}
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Implementation of Another Implementation of Another TimeTypeTimeType Class Constructor Class Constructor
TimeType :: TimeType ( int initHrs, int initMins, int initSecs )
// Constructor
// Precondition: 0 <= initHrs <= 23 && 0 <= initMins <= 59
// 0 <= initSecs <= 59
// Postcondition:
// hrs == initHrs && mins == initMins && secs == initSecs
{
hrs = initHrs ;
mins = initMins ;
secs = initSecs ;
}
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For the Final ExamFor the Final Exam
Note: You will be asked to write a simple class, without using dynamic memory. (no Copy Constructor or Destructor writing will be required.)
You should know what a copy constructor and a destructor is in concept.
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PointersPointers
• 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 linked lists,• management of dynamically allocated objects, and• as a function parameter type for passing large objects
such as arrays.
Pass-by-valuePass-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.
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Pass-by-referencePass-by-reference
sends the location (memory address)of the actual parameter
can change value ofactual parameter
CALLINGBLOCK FUNCTION
CALLED
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Obtaining Memory AddressesObtaining Memory Addresses
the address of a non-array variable can be obtained by using the address-of operator &
int x;float number;char ch;
cout << “Address of x is “ << &x << endl;
cout << “Address of number is “ << &number << endl;
cout << “Address of ch is “ << &ch << endl;
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What is a pointer variable?What is a pointer variable?
A pointer variable is a variable whose value is the address of a location in memory.
to declare a pointer variable, you must specify the type of value that the pointer will point to, for example,
int* ptr; // ptr will hold the address of an int
char* q; // q will hold the address of a char
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Using a Pointer VariableUsing a Pointer Variable
int x;
x = 12;
int* ptr;
ptr = &x;
NOTE: Because ptr holds the address of x,
we say that ptr “points to” x
2000
12
x
3000
2000
ptr
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2000
12
x
3000
2000
ptr
int x; x = 12;
int* ptr; ptr = &x;
cout << *ptr;
NOTE: The value pointed to by ptr is denoted by *ptr
Unary operator Unary operator ** is the indirection is the indirection (deference) operator(deference) operator
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int x; x = 12;
int* ptr; ptr = &x;
*ptr = 5; // changes the value // at address ptr to 5
Using the Dereference OperatorUsing the Dereference Operator
2000
12 5
x
3000
2000
ptr
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char ch; ch = ‘A’;
char* q; q = &ch;
*q = ‘Z’; char* p; p = q; // now p and q both point to ch
Another ExampleAnother Example
4000
A Z
ch
5000 6000
4000 4000
q p
Operator Operator newnew Syntax Syntax
new DataType
new DataType [IntExpression]
If memory is available, in an area called the heap (or free store) new allocates the requested object or array, and returns a pointer to (address of ) the memory allocated.
Otherwise, program terminates with error message.
The dynamically allocated object exists until the delete operator destroys it. 35
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3 Kinds of Program Data3 Kinds of Program Data
STATIC DATA: memory allocation exists throughout execution of program
AUTOMATIC DATA: automatically created at function entry, resides in activation frame of the function, and is destroyed when returning from function
DYNAMIC DATA: explicitly allocated and deallocated during program execution by C++ instructions written by programmer using operators new and delete
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Dynamically Allocated DataDynamically Allocated Data
char* ptr;
ptr = new char;
*ptr = ‘B’;
cout << *ptr;
NOTE: Dynamic data has no variable name
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ptr
‘B’
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Dynamically Allocated DataDynamically Allocated Data
char* ptr;
ptr = new char;
*ptr = ‘B’;
cout << *ptr;
delete ptr;
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ptr
NOTE: delete de-allocates the memory pointed to by ptr
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Operator delete returns to the free store memory which was previously allocated at run-time by operator new.
The object or array currently pointed to by the pointer is deallocated, and the pointer is considered unassigned.
Using Operator Using Operator deletedelete
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Operator Operator deletedelete Syntax Syntax
delete Pointer
delete [ ] Pointer
If the value of the pointer is 0 there is no effect.
Otherwise, the object or array currently pointed to by Pointer is deallocated, and the value of Pointer is undefined. The memory is returned to the free store.
Square brackets are used with delete to deallocate a dynamically allocated array. 40
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Dynamic Array Deallocation Dynamic Array Deallocation
char *ptr ;
ptr = new char[ 5 ];
strcpy( ptr, “Bye” );
ptr[ 1 ] = ‘u’;
delete ptr; // deallocates array pointed to by ptr // ptr itself is not deallocated // the value of ptr is undefined.
ptr
?
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int* ptr = new int; *ptr = 3;
ptr = new int; // changes value of ptr *ptr = 4;
What happens here?What happens here?
3
ptr
3
ptr
4
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Inaccessible ObjectInaccessible Object
An inaccessible object is an unnamed object that was created by operator new and which a programmer has left without a pointer to it.
int* ptr = new int;
*ptr = 8;
int* ptr2 = new int;
*ptr2 = -5;
8
ptr
-5
ptr2
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Making an Object InaccessibleMaking an Object Inaccessible
int* ptr = new int;
*ptr = 8;
int* ptr2 = new int;
*ptr2 = -5;
ptr = ptr2; // here the 8 becomes inaccessible
8
ptr
-5
ptr2
8
ptr
-5
ptr2
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Memory LeakMemory Leak
A memory leak is the loss of available memory space that occurs when dynamic data is allocated but never deallocated.
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int* ptr = new int;
*ptr = 8;
int* ptr2 = new int;
*ptr2 = -5;
ptr = ptr2;
delete ptr2; // ptr is left dangling
ptr2 = NULL;
Leaving a Dangling PointerA pointer that points to dynamic memory that has been de-allocated
8
ptr
-5
ptr2
8
ptr
NULL
ptr2
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Why is a destructor needed?Why is a destructor needed?
When a DynArray class variable goes out of scope, the memory space for data members size and pointer arr is deallocated.
But the dynamic array that arr points to is not automatically deallocated.
A class destructor is used to deallocate the dynamic memory pointed to by the data member.
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DynArray::~DynArray( );
// Destructor.
// POST: Memory for dynamic array deallocated.
{
delete [ ] arr ;
}
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class DynArray Destructorclass DynArray Destructor
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For the Final ExamFor the Final Exam
Note: You will not have to write source code using pointers or dynamic memory. Questions related to these topics will be multiple choice or True/False
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SEN 909 OO Programming in C++SEN 909 OO Programming in C++Final ExamFinal Exam
Multiple choice, True/False and some minimal programming will be required
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