1. Week 14 - Wednesday
CS222

2. Last time What did we talk about last time? Function pointers
Introduced C++

3. Questions?

4. Project 6

5. Quotes
If you think C++ is not overly complicated, just what is a protected abstract virtual base pure virtual private destructor, and when was the last time you needed one? Tom Cargill

6. More C++

7. Default parameter values
C++ also allows you to specify default values for function parameters
If you call a function and leave off those parameters, the default values will be used
Default parameters are only allowed for the rightmost grouping of parameters
void build(int width = 2, int height = 4) {
cout << "We built this house with " << width << " by " << height << "s."; }
build(); //We built this house with 2 by 4s.
build(3); //We built this house with 3 by 4s.
build(6, 8); //We built this house with 6 by 8s.

8. C++ example Let's write a complete C++ program that reads in:
A string
An integer
Then, it prints out the string however many times the integer specified

9. The new keyword
When you want to dynamically allocate memory in C++, you use new (instead of malloc())
No cast needed
It "feels" a lot like Java
int* value = new int(); //make an int
int* array = new int[100]; //array of ints
Wombat* wombat = new Wombat(); //make a Wombat
Wombat* zoo = new Wombat[100];
//makes 100 Wombats with the default constructor

10. The delete keyword
When you want to free dynamically allocated memory in C++, use delete (instead of free())
If an array was allocated, you have to use delete[]
int* value = new int(); //make an int
delete value;
Wombat* wombat = new Wombat();
delete wombat;
Wombat* zoo = new Wombat[100];
delete[] zoo; //array delete needed

11. C standard libraries You can compile C code with C++
Weird things can happen, but we aren't going into those subtle issues
However, you now know and love the standard C libraries
You can use them in C++ too
You just have to include different header files
C Library Header
C++ Equivalent
Purpose
ctype.h
cctype
Character manipulation
limits.h
climits
Constants for integer limits
math.h
cmath
Math functions
stdio.h
cstdio
C I/O functions
stdlib.h
cstdlib
Random values, conversion, allocation
string.h
cstring
Null-terminated string manipulation
time.h
ctime
Time functions

12. Structs in C++
A struct in C++ is actually just a class where all the members are public
You can even put methods in a struct in C++
Otherwise, it looks pretty similar
You don't have to use the struct keyword when declaring struct variables
Except in cases when it is needed for disambiguation

13. Example Here's a TreeNode struct in C++
Write a tree insertion with the following signature
struct TreeNode {
int value;
TreeNode* left;
TreeNode* right; };
void insert(TreeNode* &root, int data);

14. OOP in C++

15. Object Oriented Programming
Let's see how objects work in C++ by looking at classically important elements of OOP
Encapsulation
Dynamic dispatch
Polymorphism
Inheritance
Self-reference

16. Encapsulation Information hiding
We want to bind operations and data tightly together
Consequently, we don't want you to touch our privates
Encapsulation in C++ is provided by the private and protected keywords
Unlike Java, you mark sections as public, private, or protected, not individual members and methods
Hardcore OOP people think that all data should be private and most methods should be public

17. Encapsulation example
class A { private: int a; public: int getA() return a; } void setA(int value) a = value; };

18. Inheritance Allows code reuse Is thought of as an "is-a" relationship
C++ allows multiple inheritance, but you should only use it if you know what you're doing, usually as part of a design pattern
Deriving a subclass usually means creating a "refined" or "more specific" version of a superclass

19. Inheritance example
class B : public A { //has member and methods from A }; class C : public A { private: //has A stuff and more int c; public: int getC(){ return c; } void increment() { c++; }

20. Polymorphism
A confusing word whose underlying concept many programmers misunderstand
Polymorphism is when code is designed for a superclass but can be used with a subclass
If AudiRS5 is a subtype of Car, then you can use an AudiRS5 where you could use a Car

21. Polymorphism example
void drive( Car* c ); //defined somewhere … class AudiRS5 : public Car {}; Car car; AudiRS5 audi; drive( &audi ); //okay drive( &car ); //okay

22. Dynamic dispatch
Polymorphism can be used to extend the functionality of an existing method using dynamic dispatch
In dynamic dispatch, the method that is actually called is not known until run time

23. Dynamic dispatch example
class A { public: virtual void print() { cout << "A"; } }; class B : public A { public: void print() { cout << "B"; }

24. Dynamic dispatch example
A a; B b; A* p; a.print(); // A b.print(); // B p = &a; p->print(); // A p = &b; p->print(); // B

25. Self-reference Objects are able to refer to themselves
This can be used to explicitly reference variables in the class
Or, it can be used to provide the object itself as an argument to other methods
Self-reference in C++ is provided in part through the this keyword
this is a pointer to the object you're inside of

26. Self reference example
class Stuff { private: int things; public: void setThings(int things) this->things = things; } };

27. Self reference example
class SelfAdder { public: void addToList(List& list) list.add(this); } };

28. C++ Madness

29. Dividing up code
In industrial strength C++ code, the class declaration is usually put in a header file (.h) while the class definition is in an implementation file (.cpp)
Benefits:
Easy to see members and methods
Header files can be sent to clients without divulging class internals
Separate compilation (faster)
Easier to take care of circular dependencies

30. Dividing up code header
class Complex {
double real;
double imaginary;
public:
Complex(double realValue = 0, double imaginaryValue = 0);
~Complex(void);
double getReal();
double getImaginary(); };

31. Dividing up code implementation
Complex::Complex(double realValue, double imaginaryValue) {
real = realValue;
imaginary = imaginaryValue; }
Complex::~Complex(void) {}
double Complex::getReal()
{ return real; }
double Complex::getImaginary()
{ return imaginary; }

32. Overloading operators
In C++, you can overload operators, meaning that you can define what + means when used with classes you design
Thus, the following could be legal:
Hippopotamus hippo;
Sandwich club;
Vampire dracula = club + hippo;

33. Overloading operators
But, what does it mean to "add" a Hippopotamus to a Sandwich and get a Vampire?
Overloading operators is a bad idea
You can get confusing code
Most languages don't allow it
It C++ it is useful in two cases:
To make your objects easy to input/output using iostream
To perform mathematical operations with numerical classes (like Complex!)

34. (Partial) overloading operators header
Complex& operator=( const Complex& complex ); Complex operator+( const Complex& complex ) const; Complex operator-( const Complex& complex ) const; Complex operator-() const; Complex operator*( const Complex& complex ) const;

35. (Partial) overloading operators implementation
Complex& Complex::operator= ( const Complex& complex ) { real = complex.real; imaginary = complex.imaginary; return *this; }

36. Programming practice Let's finish the Complex type
Then, we can ask the user to enter two complex numbers
We can do the appropriate operation with them

37. What's all that const? const, of course, means constant in C++
In class methods, you'll see several different usages
Const methods make a guarantee that they will not change the members of the object they are called on
int countCabbages() const;
Methods can take const arguments
void insert(const Coin money);
Methods can take const reference arguments
void photograph(const Castle& fortress);
Why take a const reference when references are used to change arguments?

38. Templates

39. Templates
Allow classes and functions to be written with a generic type or value parameter, then instantiated later
Each necessary instantiation is generated at compile time
Appears to function like generics in Java, but works very differently under the covers
Most of the time you will use templates, not create them

40. Template method example
template<class T> void exchange(T& a, T& b ) { T temp = a; a = b; b = temp; }

41. Template classes You can make a class using templates
The most common use for these is for container classes
e.g. you want a list class that can be a list of anything
The STL filled with such templates
Unfortunately, template classes must be implemented entirely in the header file
C++ allows template classes to be separate from their headers, but no major compiler fully supports it

42. Template class example
template<class T> class Pair {
private:
T x;
T y;
public:
Pair( const T& a, const T& b ) {
x = a;
y = b; }
T getX() const { return x; }
T getY() const { return y; }
void swap() {
T temp = x;
x = y;
y = temp; };

43. Programming practice
Let's write an ArrayList class with templates!

44. Quiz

45. Upcoming

46. Next time…
STL
Lab 14

47. Reminders
Keep working on Project 6
Due next Friday