Monday, Feb 3, 2003Kate Gregory with material from Deitel and Deitel Week 5 Lab 1 comments Hand in...

transcript

Monday, Feb 3, 2003 Kate Gregorywith material from Deitel and Deitel

Week 5

• Lab 1 comments

• Hand in Lab 2

• Questions from Last Week

• Classes continued

• Lab 3

Date Week Topic ChapterHand Out Due Back Test

6-Jan-03 1Administrivia / Overview / Intro to C++ / Control Structures 1

13-Jan-03 2 Functions / Arrays, Pointers, Strings 2,3,4,5Lab 1 / Lab 2

20-Jan-03 3 Classes, Data Abstraction 6 Lab 1 5%27-Jan-03 4 More on Classes 7 Lab 3 Lab 2 5%

3-Feb-03 5 No Lecture10-Feb-03 6 Operator Overloading 8 Lab 4 Lab 3 5%17-Feb-03 Reading Break24-Feb-03 7 Inheritance 9 Lab 4 5% Midterm 25%3-Mar-03 8 Virtual Functions and Polymorphism 10 Lab 5

10-Mar-03 9 Stream IO 11 Lab 6 Lab 5 5%17-Mar-03 10 Templates 12,13 Lab 7 Lab 6 5%24-Mar-03 11 Exceptions31-Mar-03 12 File IO 14 Lab 7 5%

??? Exam Final 40%

Schedule

Lab 1 comments

• Spacing in your code

x=2*b+3;

x = 2 * b + 3;

cout << "x is " << x << endl; • Use your own sample values

• Many of you overcharged the parkers

Lab 1 comments

• Read the question– Any negative value to quit is not the same as –1

to quit– Extra testing (e.g. maximum sales, maximum

parking time) is not always helpful– Developers must create code that meets

requirements, not their improvements on requirements

What is an Object?

PrivateA ttributes

andm ethods

Public A ttributesand M ethods

System

M yO bject

• You can insist that a variable’s value never be changed:

const int a = 3;

a = 4; //will not compile

Const arguments

SomeClass::Foo1(Huge h)

{ // }

SomeClass::Foo2(Huge& h)

{ // }

SomeClass::Foo3(const Huge& h)

{ // }

Const member functions

h.x = 2;

h.setwidth(3);

h.display();

class Huge

public:

int x;

Huge();

void setwidth(int w);

void display();

class Huge

public:

int x;

Huge();

void setwidth(int w) const;

void display() const;

void Huge::display() const

cout << x;

void Huge::setwidth(int w) const

x = w;

class Huge

public:

int x;

Huge();

void setwidth(int w);

void display() const;

//h.x = 2;

//h.setwidth(3);

h.display();

Const tips

• Make member functions const as a default– If they change a member variable, take the const away

• Include const in your design from the very beginning– Adding const after the fact is miserably hard

• Use const instead of #define

Objects as Member Variables

class Employee

private:

float salary;

char* name;

Date startdate;

// rest of class

Objects as Ordinary Member Variables

void Employee::Display()

cout << “name is “ << name << endl;

cout << “salary is “ << salary << endl ;

cout << “startdate is “

<< startdate.FormatLongDate() << endl;

• No special treatment because they are objects or because they are member variables

Initializing Objects

Employee::Employee(char* n, float f)

name = n;

salary = f;

• How do I set the startdate to today?

Initializing Objects

Employee::Employee(char* n, float f)

name = n;

salary = f;

startdate.set(“today”); }

• What if no public set function has been written?

Use the Constructor

Employee::Employee(char* n, float f): startdate(“today”)

name = n;

salary = f;

• Use the public constructor

• Actually improves performance

Use the Constructor

Employee::Employee(char* n, float f): startdate(“today”), name(n), salary(f)

The friend keyword

• Making exceptions to the rules• A function can become an honourary member of

another class• It can violate encapsulation, but by avoiding a

public set or get it might be the lesser of two evils

friend

class A

friend int B::foo(A arg);

private:

int a;

// rest of class

friend

int B::foo(A arg){ arg.a = 3; // access to private a OK}int B::bar(A arg){ arg.a = 3; // access to private a not OK}

friend Tips

• Use very sparingly• Grant access to one function at a time, not the

whole class• Put the friend statements right before all the

private variables in the class definition

class Task

private:

Resource* person;

public:

void Assign(Resource* res);

// etc

class Resource

private:

Task* job;

public:

void Introduce(Task* t);

// etc

Resource* r;

// get a pointer to a resource and put it in r

Task* t;

// get a pointer to a task and put it in t

r->Introduce(t);

t->Assign(r);

• Programmer must remember to call both methods

Enforce your Business Rules

void Task::Assign(Resource* res){ person = res;} void Resource::Introduce(Task* job){ t = job; t->Assign( ??? );}

this is a useful pointer

void Task::Assign(Resource* res){ person = res;} void Resource::Introduce(Task* job){ t = job; t->Assign( this );}

Monday, Feb 3, 2003Kate Gregory with material from Deitel and Deitel Week 5 Lab 1 comments Hand in...

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