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3. More About Data Structures and ADTs:C++ Data types (Read §3.1 & §3.2)

C++ types an be classified as:

• Fundamental (or simple or scalar): A data object of one of these types is a single object.

- int, double, char, bool, complex, and the related types (unsigned, short, etc.)

- enumerations

• Structured: Collections of data

- arrays, structs, unions, classes, valarrays, bitsets, the containers and adapters in STL

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Structs vs. Classes

Similarities

1. Essentially the same syntax

2. Both are used to model objects with _______________attributes (characteristics) represented as ___________________________ (also called fields or instance variables or attribute variables).

Thus, both are used to process non-homogeneous data sets.

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Differences

1. C does not provide classes; C++ provides both structs and classes.

2. Members of a struct by default are ___________ (can be accessed outside the struct by using the the dot operator. In C++ they can be declared to be __________ (cannot be accessed outside the struct.

3. Members of a class by default are ___________ (cannot be accessed outside the class) but can be explicitly declared to be _____________

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C++'s structs and classes model objects that have: Attributes (characteristics) represented as

_________________ and

Operations (behaviors) represented as ____________________

(also called methods).

C Structs vs. C++ Classes (& Structs)

("traditional" vs "OOP")

This leads to a whole new style of programming: object-oriented. Objects are _______________, possessing their own operations — commonly called the ______________________principle — rather than being passed as a parameter to an external function that operates on them and sends them back.

Attributes

Operations

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Declaring a Class

Common Forms:

class ClassName{// private by default

Declarations of private members public:

Declarations of public members};

class ClassName{ public: //"interface" of class given first

Declarations of public members private:

Declarations of private members};

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Notes:Data members are normally placed in the private section of a class; function members in the public section.

Attributes

Data Members

Operations

Function Members

Some programmers prefer to put the private section first:- Using the default access for classes

- Can omit the private: specifier

Other programmers put the public interface of the class first and the hidden private details last. (In the text, the latter approach is used.)

Although not commonly done, a class may have several private and public sections; the keywords private: and public: mark the beginning of each.

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Access to Class Members

A particular instance of a class is called an _____________:

ClassName object_name;

Private members can be accessed ______________________ (except by ________ functions to be described later).

Public members can be accessed __________________________________________; to access them outside the class, one must use the ___________________:

object_name.public_member_name A class declaration is usually placed in a header file whose name is ClassName.h . The library is then called a class library.

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Header file for class Time — Version 1/** Time.h -------------------------------------------------------- This header file defines the data type Time for processing time Basic operations are: Set: To set the time Display: To display the time ----------------------------------------------------------------------*/

#include <iostream>using namespace std;

class Time{/******** Member functions ********/public:

/* Set sets the data members of a Time object to specified values. * * Receive: hours, the number of hours in standard time * minutes, the number of minutes in standard time * AMPM ('A' if AM, 'P' if PM * Postcondition: The Time object containing this function has its * myHours, myMinutes, and myAMorPM members set to hours, * minutes, and am_pm, respectively, and myMilTime to * the equivalent military time ********************************************************************/

void Set(unsigned hours, unsigned minutes, char am_pm);

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Notes: 1. "my" in data members names is a reminder of internal ("I can do it

myself") perspective.

2. const at end of Display()'s prototype makes it a ___________________________which means it ___________________________________________________________Good idea to protect data members from accidental modification.

/* Display displays time in standard and military format using * output stream out. * * Receive: ostream out * Output: The time represented by the Time object containing * this function * Passes back: The ostream out with time inserted into it *****************************************************************/

void Display(ostream & out) const;

/********** Data Members **********/private: unsigned myHours, myMinutes; char myAMorPM; // 'A' or 'P' unsigned myMilTime; // military time equivalent}; // end of class declaration

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3. Why make data members private?

"Hidden" data members: Cannot be accessed outside class Application programs must interact with an object through its _____________ ________________________ control interaction between programs and class. Application programs need not know about implementation!

Implementation may___________ (improve storage, simpler algorithms. etc.)

If interface is constant, programs using an object ____________________.

What's wrong with tying application code to implementation details? A change in implementation forces a change in the application code

Increased upgrade time. Increased programmer cost Decreased programmer productivity Reduced profits due to

— Delayed releases/upgrades— Loss of customer confidence in software reliability

Always define data members of a class as private.

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Implementation of a Class

Class declaration contains:

• Declarations of data members • Prototypes (declarations) of function members

Definitions of function members are not usually placed in class declaration Avoid cluttering up the interface

Definitions placed outside the class declaration must tell compiler where the corresponding declaration/prototype is:

Use the ___________________which has the form

______________________________

(the____________or ________ name of ItemName.)

This applies also to _____________and ________ declared within a class.

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Example:

class Something{ public: ____________ const int CAPACITY = 100; typedef double ArrayType[CAPACITY];

void Print(ArrayType a, int itsSize); . . .}; . . .

______________ArrayType x = {0};

for (int i = 0; i < _________________CAPACITY; i++) . . .void Something::Print(Something::ArrayType a, int itsSize){ . . . }

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Traditionally, definitions of member functions have been put in an implementation file ClassName.cpp corresponding to the class' header file. This is done to enforce _____________________— separating the ________________ of the ADT from its ____________________________ (Unfortunately, the class data members, which store data and are therefore part of the implementation, must be in the .h file.)

With the increasing use of ______________, however, this practice is becoming less common because current compiler technology doesn't permit this split for templates — everything has to be in the same file. Thus the reason for dropping the ".h" from standard class libraries. They're really class-template libraries, and there are therefore no corresponding ".cpp" files.

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Implementation of class Time — Version 1

// Time.cpp -- implements the Time member functions #include "Time.h

/*** Utility functions ***/

/* ToMilitary converts standard time to military time. Receive: hours, minutes, am_pm Return: The military time equivalent Could implement this as a private class method*/

int ToMilitary (unsigned hours, unsigned minutes, char am_pm){ if (hours == 12) hours = 0; return hours * 100 + minutes + (am_pm == 'P' ? 1200 : 0);}

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Implementation of class Time — cont.//--- Function to implement the Set operation

void __________________(unsigned hours, unsigned minutes, char am_pm){ // Check _____________________________ if (hours >= 1 && hours <= 12 && minutes >= 0 && minutes <= 59 && (am_pm == 'A' || am_pm == 'P')) { myHours = hours; myMinutes = minutes; myAMorPM = am_pm; myMilTime = ToMilitary(hours, minutes, am_pm); } else cerr << "*** Can't set time with these values ***\n"; // Object's data members remain unchanged}

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//--- Function to implement the Display operation

void ________________(ostream & out) ____________{ out << myHours << ':' << (myMinutes < 10 ? "0" : "") << myMinutes << ' ' << myAMorPM << ".M. (" << myMilTime << " mil. time)";}

Implementation of class Time — cont.

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Test driver for class Time

#include "Time.h"#include <iostream>using namespace std;

int main(){ _____________________________; _______________________________________________; cout << "We'll be eating at "; _______________________________________________; cout << endl;}

Execution:

We'll be eating at 5:30 P.M. (1730 mil. time)

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Object-Oriented Perspective

Procedural: Send object off to some function for processing

OOP: Send a message to the object to operate on itself.

To set my digital watch to 5:30 P.M., I don't wrap it up and mail it off to Casio. I push a button!

To display the time on my watch, I don't wrap it up and mail it off to Casio and have them tell me what time it is. I have it display the time itself, perhaps pushing a button to turn on the backlight so I can see it .

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Notes:

1. Member functions: "Inside" an object, so don't pass object to them as a parameter. (They receive the object to be operated on implicitly, rather than explicitly via a parameter.)

Non-member functions: "Outside" an object, so to operate on an object, they must receive it via a parameter.

2. Public items must be qualified when referred to outside the class declaration:ClassName::ItemName

Public constants are usually declared static so they are global class properties that can be accessed by all objects of that class type rather than each object having its own copy.

3. Simple member functions: Usually specified as _______________ functions —

suggests to compiler to replace a function call with ______________________ ________________________________________________________________

— saves overhead of function call.

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Two ways to inline a class function member:

1. Prototype in class declaration; inline definition ______________

____________________________________________________qualifying the name as usual.

In ClassName.h:

class ClassName{ public: RetType SimpleFun(param_list); //prototype . . .};

__________ RetType ClassName::SimpleFun(param_list)

{ . . . } // definition2.Put function’s __________ (instead of prototype) __________

_______________________— compiler will treat it as inlined.

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Operations that modify data members must ____________________________________

Class Invariant: A condition (boolean expression) that ensures that the __________________________________________

Example: 1 < myHours < 12 && 0 < myMinutes < 59 &&

myAMorPM == 'A' or 'P' && 0 < myMilTime < 2359

Then other operations can be sure data members have valid values.

How?

1. Use an if statement — see Set()

2. Use __________(class_invar); (must #include <cassert>)

continue execution halt execution and display error messagetrue false

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3._________________________that the calling function can ________ and take appropriate action:

//----- Function to implement the Set operation -----void Time::Set(unsigned hours, unsigned minutes, char am_pm){ // Check class invariant if (hours >= 1 && hours <= 12 && minutes >= 0 && minutes <= 59 && (am_pm == 'A' ||am_pm == 'P')) { . . . } else { char error[] = "*** Illegal initializer values ***\n"; ___________ error

}}

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To catch this exception, a calling function might contain:

________ { mealTime.Set(13, 30, 'P'); cout << "This is a valid time\n";}__________________________________ { cerr << "ERROR: " << badTime << endl; exit(-1);}cout << "Proceeding. . .\n";

When executed, the output produced will be ERROR: *** Illegal initializer values ***

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Class ConstructorsConstructing an object consists of:

(1) ___________________ for the object, and(2) ____________ the object.

In our example, after the declaration

Time mealTime;

memory has been allocated for object mealTime and it's datamembers have some default (perhaps "garbage") initial values.Need to:

Specify initial values for mealTime Provide default values to be used if no initial values are

specified.

This is the role of a class' ________________. (Later, it will also allocate memory.)

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Class Constructors - Properties1. Names are always the same as the class name.2. Initialize the data members of an object with default values or

with values provided as arguments.3. Do not return a value; have no return type (not even void).4. Often simple and can be inlined.

5. Called _______________________________________________.

6. If no constructor is given in the class, ______________________ _____________________________which allocates memory and initializes it with some default (possibly garbage) value.

A default constructor is one that is used when the declaration of an object contains _____________________________:

ClassName object_name;An _________________________ constructor is used for declarations with initial values:

ClassName object_name(list-of-init-values);

7. If we supply a class constructor, we must also provide a ____________________________ or we can't use first kind of declaration.

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Constructors for Time classIn Time.hclass Time{ public: /* --- Construct a class object (default). * Precondition: A Time object has been declared. * Postcondition: Data members initialized to 12, 0, 'A', and 0. ****************************************************************/ _____________________

/* --- Construct a class object (explicit values). * Precondition: A Time object has been declared. * Receive: Initial values initHours, initMinutes,and * initAMPM * Postcondition: Data members initialized to initHours,initMinutes, * initAMPM, & correspoding military time **********************************************************/__________________________________________ _____________________ ___________________ . . .// other member function prototypes

private:/********** Data Members **********/ . . .}; // end of class declaration

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Constructors for Time class - ImplementationIn Time.h, after class declaration:

__________________________{ myHours = ____; myMinutes = ____; myAMorPM = _____; myMilTime = ___;}

In Time.cpp:

_______________(unsigned initHours, unsigned initMinutes, char initAMPM){ // Check class invariant assert(initHours >= 1 && initHours <= 12 && initMinutes >= 0 && initMinutes <= 59 && (initAMPM == 'A' || initAMPM == 'P'));

myHours = _________________; myMinutes = _______________; myAMorPM = ________________; myMilTime = ToMilitary(initHours, initMinutes, initAMPM);}

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Testing #1:

Time ______________________________, //default constructor ______________________________; //explicit-value constructor

Create and initialize 2 Time objects:

mealTime.Display(cout); cout << endl;bedTime.Display(cout); cout << endl;

Execution:12:00 A.M. (0 mil. time)11:30 P.M. (2330 mil. time)

mealTime

myHoursmyMinutesmyAMorPMmyMilTime

Function members

Default Constructor

bedTime

myHoursmyMinutesmyAMorPMmyMilTime

Function members

Explicit Value Constructor

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Constructors for Time class — Default Arguments

Can combine both constructors into a single constructor function by using _______________________:

Replace constructors in Time.h with:

/*--- Construct a class object. Precondition: A Time object has been declared. Receive: Initial values initHours, initMinutes, and initAMPM (defaults 12, 0, 'A') Postcondition: Data members initialized to initHours, initMinutes, initAMPM, & correspoding military time.*/

Note: Any parameter with default argument must appear after all parameters without default arguments.

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Testing:

Time mealTime, t1(5), t2(5, 30), t3(5, 30, 'P');

Creates 4 Time objects:

mealTime.Display(cout); cout << endl;t1.Display(cout); cout << endl;t2.Display(cout); cout << endl;t3.Display(cout); cout << endl;

Execution:

12:00 A.M. (0 mil. time)5:00 A.M. (500 mil. time)5:30 A.M. (530 mil. time)5:30 P.M. (1730 mil. time)

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Copy Operations

Two default copy operations are provided:

1. Copy in ______________ (via _________________________)

2. Copy in ______________ (via _________________________)

Each makes a _______________________________ allocated to the data members of the object.

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Examples:

Both:1. Allocate memory for t2. Copy data members of bedTime so t is a copy of bedTime

In contrast:Time t = _________________________

calls the _________________________ to construct a (temporary) Time object and then copies it into t.

Note: These are _________________; a default ______________________ is called.

What aboutTime t = 3;

?

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There is a default copy operation for assignment.

Example:

t = mealTime;

copies the members of mealTime into t, replacing any previous values:

120A0

It returns __________________________________________

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Access Member FunctionsData members are private: they cannot be accessed outside the class. To make the values stored in some or all of these members accessible, provide____________(or extractor) member functions

Example: To provide access to myHours of class Time.(Access for the remaining members is analogous.)

simply retrieves and returns the value stored in a data member inline, because it's simple

prototype (and define) as a const function

Add in Time class declaration/* Hour Accessor * Return: value stored in myHours data member of * Time object containing this function */_______________________________________

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Add below Time class declaration

inline unsigned Time::Hour() const{______________________}

Testing:

Time mealTime; . . .cout << "Hour: " << mealTime.Hour() << endl;

Execution:

Hour: 12

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Output and Input

Add output operation(s) to a class early so it can be used for debugging other operations.

Example: overload operator<< for a Time object

Instead of: cout << "We'll be eating at " ;

_______________________________________cout << endl;

we can write:cout << "We'll be eating at " _______________________________________

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Overloading operators

In C++, operator can be implemented with the functionoperator().

If a member function of a class C, and a is of type C, the compiler treats a b as

_________________________

If not a member function of a class C, the compiler treats a b as

_________________________

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Overloading Output Operator <<Can operator<<() be a member function?______, because the compiler will treat

cout << t

as________________________

which means that operator<<(const Time &) would have to be a____________________________________(or cout be of type Time)and we can't (or don't want to) modify standard C++ classes.

Putting the prototypeostream& operator<<(ostream & out, const Time& t);

inside our class declaration producs a compiler error like:'Time::operator <<(ostream &, const Time &)' must take exactly one argument

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Why is out a reference parameter?So corresponding actual ostream argument gets modified

when out does.Why is t a const reference parameter?

Avoid overhead of ____________________________________

Why is return type ostream & (a reference to an ostream)?Else a __________________ is returned.

Why return out?So we can __________________________.Since << is ________-associative: cout << t1 << endl << t2 << endl; operator<<(cout, t1) << endl << t2 << endl;

first function must return _________

_______ << endl << t2 << endl; operator<<(cout, endl) << t2 << endl; _______ << t2 << endl;

. . .

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Method 1: Put definition in .h file, after class declaration, and have it

__________________________________________. Inline it, because it's simple.

. . .} // end of class declaration. . ./* operator<< displays time in standard and military format. Receive: ostream out and Time object t Output: time represented by Time object t Pass back: ostream out with t inserted into it Return: out*/

_______ ostream & operator<<(ostream & out, const Time & t){

}

Overloading << for a Class

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Method 2: Define operator<<()outside the class declarationas a _______________ function and:(i) use _________________ to display data members, or(ii) declare it to be a __________in the class declaration.

In class declaration

/* doc. as before */

_________ ostream & operator<<(ostream & out, const Time & t);

Outside class declaration (in .cpp file)ostream & operator<<(ostream & out, const Time & t)

{ out << t.myHours << ':' << (t.myMinutes < 10 ? "0" : "") << t.myMinutes << ' ' << t.myAMorPM << ".M. (" << t.myMilTime << " mil. time)"; return out;}

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Friend Functions

A function that a class declares as a friend is a

_______________ function to which the class has granted

permission to ________________________________________.

Note: Because a friend function is not a function member:

Don't ____________________________ with class name and scope operator (::).

Don't put ____________ in definition.

It receives the object on which it operates as a parameter.

It uses the dot operator to access the data members.

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To add an input operator to our Time class, we proceed in much the same way as for output. We could either:

1. Add a member function ReadTime() that reads values and stores them in the data members of a Time object; then call it from non-member function operator>>().

2. Declare operator>>() to be a friend function so that it can access the data members of a Time object and store input values in them.

Is one of the two methods for input/output preferred?

We'll see later when we study inheritance and polymorphism that the first method is preferred (or perhaps required).

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Relational Operators (<)Specification:

Receives: Two Time objectsReturns: True if the first object is less than the second; false otherwise.

Should operator<() be a member function?

Internal perspective: I compare myself with another Time object anddetermine if I am less than that other object

External perspective: Two Time objects are compared by an external functionto determine if the first is less than the second.

OOP: "I-can-do-it-myself" principle ( objects self-contained):Use member functions whenever possible.

Rephrased specification:Receives: A Time object (and the current object implicitly)Returns: True if I (the Time object containing this function) am

less than the Time object received; false otherwise.

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However . . .

// Internal perspective : Add to Time.h

class Time{ public: // member functions . . ./***** Relational operators *****//* operator< determines if one Time is less than another Time * Receive: A Time t (and the current object implicitly) * Return: True if time represented by current object is < t. */bool operator<(const Time & t) const;. . .}; // end of class declaration

inline bool Time::operator<(const Time & t) const{ return myMilTime < t.myMilTime; }

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Caveat re Operator OverloadingInternal perspective may lead to seeming inconsistencies:

Example: Suppose a and b are objects of type class C.a < b okay?

Yes, equivalent to _________________________

b < a okay?Yes, equivalent to _________________________

a < 2 okay?_____, if there is a ___________________________________,since this is then equivalent to _________________________

2 < a okay?____, equivalent to ___________________which is meaningless.

May confuse an application programmer to support a < 2 but disallow 2 < a. probably best to use friends here.

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Overloaded Operator as FriendExternal perspective: (Permits a < 2 and 2 < a , if 2 can be promoted)class Time{public: // member functions ... /* operator< * Receive: Two Times t1 and t2 * Return: True if time t1 is less than time t2/ */

___________________________________________________________________); ...}; // end of class declaration

inline bool Time::operator< (const Time& t1, const Time& t2)

{return ______________________________________; }

Or don't use friend and compare values obtained by accessors.

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Adding Increment/Decrement Operators

Specification:Receives: A Time object (perhaps implicitly)Returns: The Time object with minutes incremented by 1 minute.

Question: Should it be a member function? _________

Add to Time.h:

/***** Increment operator *****/

/* --- Advance() increments a Time by 1 minute.

Postcondition: The Time object has its minutes incremented by 1.-----------------------------------------------*/

__________________________________

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Add to Time.cpp:

//----- Function to implement Advance() -----void Time::Advance(){ myMinutes++; myHours += myMinutes / 60; myMinutes %= 60; myHours %= 12; if (myMilTime == 1159) myAMorPM = 'P'; else if (myMilTime == 2359) myAMorPM = 'A'; // else no change myMilTime = ToMilitary(myHours, myMinutes, myAMorPM);}

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We could replace Advance() with overloaded operator++().

Question: How do we distinguish between prefix ++ and postfix ++?

++

(which is not used in the definition.)

Postfix ++:

Solution: In C++, when the

Compiler encounters: It looks for:

Prefix ++:

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Redundant Declarations

Class Time might be used in different programs, libraries, etc., so it could be included several times in the same file

e.g., Program needs Time class, so it #includes "Time.h"Program also needs library Lib, so it #includes "Lib.h" . . . but Lib.h also #includes "Time.h"

This can cause "redeclaration" errors during compiling.

How do we prevent the declarations in Time.h from being included more than once in a file?

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Conditional CompilationWrap the declarations in Time.h inside preprocessor directives.(Preprocessor scans through file removing comments, #including files, and processing other directives (which begin with #) before the file is passed to the

compiler.) #ifndef TIME Usually the name of the class in all caps#define TIME

::

#endif

The first directive tests to see whether the identifier TIME has been defined.

If not defined:Proceed to second directive ( define TIME )Continue to the #endif and beyond.

If defined:Preprocessor removes all code that follows until a#elsif, #else, or #endif directive encountered.