1. CS3340 – OOP and C++
L. Grewe

2. C++ C++ is an object-oriented programming language. Who created C++?
Bjarne Stroustrup, while at AT&T.
(now, a professor in Computer Science at Texas A&M University)

3. Overview C++ basics (see course website)
C++ and OOP concepts revisited

4. Code Reuse Two ways of code reuse: composition & inheritance
Composition (“has-a” relationship):
An object of a class has an object of another class in it. Use predefined code of a class by creating an object of the class.
Inheritance (“is-a” relationship):
A child class inherits everything from its parent class. Use predefined code of a class by sub-classing from it.

5. composition (has-a) class CWheel { private: float air-pressure;
public:
void inflate(); …
}; // predefined class
class CPassengerCar {
private:
int number-of-seats;
CWheel fl-wheel, fr-wheel;
CWheel rl-wheel, rr-wheel;
public: … };

6. inheritance (is-a) “a passenger car is a car” class CCar {
“a truck is a car”
“a race car is a car”
class CCar {
private:
CEngine engine;
CBreak break;
public:
void accelerate();
void stop(); …
}; // predefined class
class CPassengerCar : public CCar {
private:
int number-of-seats;
CWheel fl-wheel, fr-wheel;
CWheel rl-wheel, rr-wheel;
public: … };

7. Encapsulation
Grouping data and operations (functions/methods) together to facilitate code reuse.
Controlling the access of the members. (Private members are hidden and can only be accessed by the member functions of the class. Users can only use the given public functions to alter the private data members).
class CCar {
private:
CEngine engine;
CBreak break;
public:
void accelerate();
void stop(); … };

8. Encapsulation class CCar { protected: CEngine engine;
CBreak break;
public:
void accelerate();
void stop(); … };
Protected members are hidden and can only be accessed by the member functions of the class and its decedent classes.

9. Polymorphism One method behaves differently for different objects.
class CShape {
private: int color;
public: virtual float area() { };
// a virtual function can be overridden by the children };
class CCircle : public CShape{
public:
float area() {return (pi * r * r)}; };
class CRect : public CShape{
public:
float area() {return (w*h)}; };

10. Polymorphism One function behaves differently for different objects.
CShape *shapes[4];
CCircle *c1 = new CCircle(5);
CCircle *c2 = new CCircle(10);
CRect *r1 = new CRect(4,5);
CRect *r2 = new CRect(8,5);
shapes[0] = (CShape *) c1; // cast to parent allowed
shapes[1] = (CShape *) c2; // cast to parent allowed
shapes[2] = (CShape *) r1; // cast to parent allowed
shapes[3] = (CShape *) r2; // cast to parent allowed
for (I=0; I<4; I++) cout << shapes[I]->area() << endl;

11. Interface in C++ ……Use Abstract Class
Polymorphism…. interfaces
There is no “Interface” in C++.
The workaround is to define abstract classes with pure virtual functions.
Pure virtual functions: have only function headers (APIs), but no function bodies.
virtual return-type function-name (argument list) = 0;
Abstract classes: have one or more pure virtual functions; can be used for inheritance by child classes, can not be used for instantiation of objects. The child classes are required to implement all pure virtual functions with predefined APIs.

12. Polymorphism Setting up standard interfaces
Polymorphism makes it possible for objects of different child classes to have the same interface.
To enforce a standard interface, one can make the parent class an abstract class and subclass from it.
An abstract class is a class containing a pure virtual function. One can’t instantiated an abstract class. It is just for setting up standard interfaces. Its child classes must override and implement the pure virtual function. (A regular virtual function is not required to be overridden by the child classes and it is inherited if it is not overridden.)

13. Polymorphism class CShape { public: virtual float area() = 0;
// a pure virtual function
}; // CShape a-shape; not allowed.
class CCircle : public CShape{
public:
float area(); // must be implemented. };
class CRect : public CShape{
public:
float area(); // must be implemented. };

14. Common OOP need - Iterators
Collections, Iterators --- and templates
traverse a collection of objects from the beginning to the end.
iterators have been implemented for all C++ collection classes (e.g. vector).
Have templates (like generics in Java)
vector<Shape *> shapes; …
vector<Shape *>::iterator it = shapes.begin();
    while(it != shapes.end()) (*it++)->display();

15. Coding with an IDE (MS Visual Studio 2XXX)
The actual sequence will depend on your version of
MS Visual Studio
Using Start->Program Files-> MS Visual Studio 2XXX-> MS Visual Studio XXXX
Select C++ as default environment if prompted to.
File->New->Project->
Other Languages->Visual C++->Win32->Win32 Console Application
Name: test
Location:
My Documents\Visual Studio 2XXX\Projects (fix this to a location…like your USB fob that you will remember to take with you)

16. Some Review and other things
I/O , file I/O
Templates
Vector
Protection types
pointers

17. Console IO console input an object of iostreams
Reading Input: cin
console input
an object of iostreams
only supports one operator >>
reads input for its arguments, one at a time
auto converts input to the type of the arguments
Displaying Output: cout
console output
only supports one operator <<
sends output to the console for its arguments, one at a time
auto converts output of the type of the arguments for display
display format can be specified

18. File IO #include <string>
#include <fstream> // file io streams
#include <iostream> // file io streams
using namespace std;
int main() {
string infile, outfile;
cout << "Enter input file name: \n";
cin >> infile;
cout << "Enter output file name: \n";
cin >> outfile;
ifstream in(infile.data()); // Open for reading
ofstream out(outfile.data()); // Open for writing
string s;
while(getline(in, s)) // Discards newline char
out << s << "\n"; // ... must add it back }

19. Protection Type public, private and protected
public members are accessible to all.
protected members are accessible to
derived class.
private accessible only to same class.

20. vector (smart array) To use: #include <vector> To define:
vector <type> v;
To add an element:
v.push_back(object);
To access an element:
v[i] (just like an array)
Eaxmples:
vector<int> vi; vector<string> vs;
int i; string s;
cin >> i >> s;
vi.push_back(i); vs.push_back(s);
cout << vi[0] << vs[0];

21. Address of a Variables & Operator & returns the address of an variable
e.g.: &i, &ia[0], &ia[1]
The address of a memory is expressed as a hex number
e.g.: 0xffaabbcc

22. Pointers in C and C++ Pointer A pointer is a named memory space.
The size of the memory is determined by the OS (32 bits, 64 bits, …), and it determines the maximum addressing space of the OS.
The memory space of a pointer stores the address of another memory space. We usually say, the pointer points to the memory space.
The size of the pointed memory space is determined by the type of the pointer.
A pointer is declared as
type * name;
Example: int * ip //ip (4 bytes of memory for a 32bit OS)
0xffaabbcc
int i = 8;
ip = &i; i 8