COM262 Object Development

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COM262 Object Development
Driving (arrays of) classes with main()and menus
Additional O-O features const initialisation
list for const friend
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Milestone testPart 1 Problem specification ?
code
Class declaration
Class definition function bodies
Main() program
Part 2 Chop-up code ? class.h, class.cpp,
main.cpp
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• FileNew 6other ConsoleWizard
• VCL, Multithreaded
• Get rid of pragma etc.
• Get rid of main( arguments )
• Save as class.cpp
• Save Project as classProject.bpr
• Write a class
• Add-in your string and IO header files
  (cutpaste)
• FileNew other hpp file
• FileNew other cpp file
• (add to Project)

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HEADER FILEStudent.hifndefdefineendif

• include ltiostream.hgt
• include ltstringgt // included for string classes
• using stdstring
• class Student
• private
• string name
• int mark
• public
• // default constructor function
• Student( void )
• Student( string hs, int m )
• void AddMark( int extra )
• int GetMark( void )
• string GetName( void )
• void PrintDetails( int index )

PRIVATE DATA
PUBLIC FUNCTIONS
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CONSTRUCTORS FUNCTIONSStudent.cpp

• include Student.h
• include ltiostream.hgt
• include ltstringgt // included for string classes
• using stdstring
• StudentStudent( void )
• cout ltlt "Enter new student's name "
• cin gtgt name
• mark 0
• StudentStudent( string hs, int m )
• name hs
• mark m

void StudentAddMark(int extra) mark
extra int StudentGetMark(void) return
mark
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• include Student.h
• include ltconio.hgt
• include ltiostream.hgt
• include ltstringgt
• using stdstring
• void main()
• int av_mark
• Student a_Student(Hector", 28)
• Student b_Student( Morag", 45)
• a_Student.AddMark( 33 )
• b_Student.AddMark( 45 )
• // calculate average mark
• av_mark ( a_Student.GetMark()
  b_Student.GetMark() ) / 2
• // display the information
• cout ltlt "The average mark was " ltlt av_mark ltlt
  endl
• getch()

MAIN() PROGRAM StudentApp.cpp
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main() function and menu

• switch ( choice )
• case 1 // get extra and add marks
• cin gtgt extra_marks
• a_student.AddMark(extra_marks)
• break
• case 2
• a_student.PrintDetails()
• break
• case 3
• mark a_student.GetMark()
• cout ltlt "Current mark is " ltlt mark
• break
• case 4 // exit
• return 0

• int main()
• int mark, extra_marks, choice
• Student a_student(Anakin", 12)
• while ( 1 ) // forever loop until exit option
• cout ltlt "Select your option"
• cout ltlt "1. Add some marks"
• cout ltlt "2. Display student details"
• cout ltlt "3. Display just the mark"
• cout ltlt "4. Exit program."
• // get user's menu selection into a variable
• cin gtgt choice

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• const int NO_STUDENTS3
• displayMenu()
• main()
• int choice, i, extra_marks
• String name
• Student studentsNO_STUDENTS
• while ( 1 ) // forever loop until exit
• displayMenu()
• // get user's menu selection
• cin gtgt choice

switch ( choice ) case 1 break case 2
break case 9 break default //
end switch // end while // end main
main() function, menu and array of students
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case 2 // get student name print mark
cin gtgt name for ( i0 i lt NO_STUDENTS i )
if ( name
studentsi.GetName() )
break // exit for loop
if ( i NO_STUDENTS ) // exit
switch cout ltlt "No student
found" break // found student
details ! studentsi.PrintDetails( )
break // exit switch
case 1 // get student index, add marks cin gtgt
i gtgt extra_marks studentsi.AddMark(
extra_marks ) break
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Additional O-O features
const initialisation list for const friend

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const (Constant) Objects and const Member
Functions

• Principle of least privilege
• Only give objects permissions they need, no more
• Keyword const
• Specify that an object is not modifiable
• Any attempt to modify the object is a syntax
  error
• Example
• const Time noon( 12, 0, 0 )
• Declares a const object noon of class Time and
  initializes it to 12

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• const objects require const functions
• Member functions declared const cannot modify
  their object
• const must be specified in function prototype and
  definition
• Prototype
• ReturnType FunctionName(param1,param2) const
• Definition
• ReturnType FunctionName(param1,) const
• Example
• int AgetValue() const return
  privateDataMember
• Returns the value of a data member but doesnt
  modify anything so is declared const
• Constructors / Destructors cannot be const
• They need to initialize variables, therefore
  modifying them

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class Time public // default
constructor Time( int 0, int 0, int 0 )
void setTime( int, int, int ) // set
time // get functions (normally declared
const) int getHour() const // return
hour int getMinute() const // return
minute int getSecond() const // return
second // print functions (normally declared
const) void printConst() const // print
time void print() // print
time private int hour // 0
23 int minute // 0 59 int second
// 0 59
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int main() Time wakeUp( 6, 45, 0 ) //
non-constant object const Time noon( 12, 0, 0 )
// constant object //
COMPILER ERRORS MEMBER FUNCTION
OBJECT wakeUp.setHour( 18 ) // non-const
non-const noon.setHour( 12 ) // non-const
const wakeUp.getHour() // const
non-const noon.getMinute() // const
const noon.printStandard() // non-const
const
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const (Constant) Objects and const Member
Functions

• Member initializer syntax
• Data member age_EFFECT in class Person
• constructor for Increment is modified as follows
• Person Person ( int c, int i ) age_EFFECT
  ( i ) count c
• age_EFFECT ( i ) initializes age_EFFECT to i
• All data members can be initialized using member
  initializer syntax
• consts and references must be initialized using
  member initializer syntax
• Multiple member initializers
• Use comma-separated list after the colon

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class Person public Person( int c 0, int
i 1 ) void getting_older() wisdom
age_effect void print() const private i
nt wisdom const int age_effect // const data
member
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// Constructor for class Increment Person
Person ( int c, int i ) // initializer for const
member age_effect( i ) wisdom c
// Print the data void Person print()
const cout ltlt jedi mastery " ltlt wisdom
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Composition Objects as Members of Classes

• Composition, AGGREGATION
• Class has objects of other classes as members
• Construction of objects
• Member objects constructed in order declared
• Not in order of constructors member initializer
  list
• Constructed before their enclosing class objects
  (host objects)

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class Date public // default
constructor Date( int 1, int 1, int 1900
) // print date in month/day/year format void
print() const // provided to confirm
destruction order Date() private int
month // 1-12 int day // 1-31 based on
month int year // any year // utility
function to test proper day // for month and
year int checkDay( int )
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// Constructor Confirm proper value for
month // call utility function checkDay // to
confirm proper value for day. DateDate( int
mn, int dy, int yr ) // validate the month if
( mn gt 0 mn lt 12 ) month mn else
month 1 cout ltlt "Month " ltlt mn ltlt "
invalid. \n" year yr // should
validate yr day checkDay( dy )// validate the
day
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class Employee public Employee( string,
string, int, int, int, int, int, int
) void print() const Employee()
private string firstName string
lastName const Date birthDate const Date
hireDate
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EmployeeEmployee( string fname, string
lname, int bmonth, int bday, int byear, int
hmonth, int hday, int hyear ) birthDate(
bmonth, bday, byear ), hireDate( hmonth, hday,
hyear ) firstName fname lastName
lname main() Employee e( "Bob", "Jones",
7, 24, 1949, 3, 12, 1988 )
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friend Functions and friend Classes

• friend function and friend classes
• Can access private and protected members of
  another class
• friend functions are not member functions of
  class
• Defined outside of class scope
• Properties of friendship
• Friendship is granted, not taken
• Not symmetric (if B a friend of A, A not
  necessarily a friend of B)
• Not transitive (if A a friend of B, B a friend of
  C, A not necessarily a friend of C)

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friend Functions and friend Classes

• friend declarations
• To declare a friend function
• Type friend before the function prototype in the
  class that is giving friendship
• friend int myFunction( int x )
• should appear in the class giving friendship
• To declare a friend class
• Type friend class Classname in the class that is
  giving friendship
• if ClassOne is granting friendship to ClassTwo,
• friend class ClassTwo
• should appear in ClassOne's definition

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• 1. Class definition
• 1.1 Declare function a friend
• 1.2 Function definition
• 1.3 Initialize Count object

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counter.x after instantiation 0 counter.x after
call to setX friend function 8
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• (Previous program without friend declared)

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  Compiling... Fig07_06.cpp D\books\2000\cpphtp3\
examples\Ch07\Fig07_06\Fig07_06.cpp(22)
error C2248 'x' cannot access private member
declared in class 'Count'
D\books\2000\cpphtp3\examples\Ch07\Fig07_06\
Fig07_06.cpp(15) see declaration of
'x' Error executing cl.exe.   test.exe - 1
error(s), 0 warning(s)
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TUTORIAL

• Milestone Test 2