Fundamentals of C++

1. Fundamentals of C++ Yingcai Xiao 09/03/08

2. Class Definition • IO • Template • vector • C • Pointer • Dynamic Memory Allocation Outline

3. Example: How to define a class (user-defined data type) class Rectangle { protected: int width; int height; public: Rectangle () { } Rectangle (int cx, int cy) {width = cx; height = cy;} int area() {return with*height;} };

4. Class Name; In C++: “Rectangle rect” declares an object of class Rectangle. rect Instantiating a Class in C++ “rect” is the name of a memory space that stores a Rectangle object.

5. 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 • an object of iostreams • 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 Console IO

6. #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 } ///:~ File IO

7. <T> x; Where type, T, is a variable too. T : int => int x; T : float => float x; Template (Type Variables)

8. 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]; vector (smart array)

9. Data storage types: • int, float, char, array (e.g., int ia[4];), enum, struct, union • No classes in C. • Computation operators: • Math: +, -, *, /, %, =, -=, +=, *=, /= • Logical: <, >, <=, >-, ==, !=, ||, &&, • bitwise: |, &, >>, <<,^ • Control statements: • if-else, while, do-while, for, switch, C in C++

10. Pointers in C and C++

11. Variable • A variable is a named memory space. • The memory space stores the value of the variable. • The size of the memory is determined by the variable’s type. • The limit of the variable is determined by the size of the memory and the type of the variable. Example: int i = 8; i(4 bytes of memory) 8 Variables in C and C++ • The memory of a variable is allocated at compile time. • The memory of an automatic variable is automatically freed at run time when the variable is no longer in used. • By default all variables are automatic. The following statements are the same: int i = 8; auto int i = 8;

12. An array of memory can be allocated as • int ia[2]; • ia[0] = 1; • ia[1] = 2; • or • int ia[2] = {1,2}; • or • int ia[] = {1,2}; Arrays in C and C++ Example: int ia[2] = {1,2}; ia[0] ia[1] (4 bytes each) 1 2 • Array memories are “allocated” at compile time.

13. & • 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 Address of a Variables

14. 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; Pointers in C and C++ Example: int * ip; ip(4 bytes of memory for a 32bit OS) 0xffaabbcc int i = 8; ip = &i; i 8

15. Memories can be allocated at run-time (dynamic memory allocation). • “new” is the operator for DMA. • It allocates a memory and returns its address (but gives it no name.) • A pointer is needed to store the address of a dynamically allocated memory. • The size of the memory is determined by the argument supplied to “new”. • Operator “*” dereference a pointer to access the memory it points to. • A pointer needs to point to a valid memory before being dereferenced. • A dereferenced pointer can be used just like a named memory (a regular variable). Dynamical Memory Allocation (DMA) int * ip; ip(4 bytes of memory for 32bit OS) 0xffaabbcc no name ip = new (int); 8 *ip = 8; cout << *ip;

16. There are two ways to dereference a DMA object. • * • -> • Example: • Dog *dp; • dp = new Dog(“Stommy”); • cout << (*dp).getName(); • cout << dp->getName(); • Exam Pet.cpp Dereferencing a DMA object

17. /* Pet.cpp. This program demonstrates OOP constructs in C++ Dr. Xiao (9/6/07), adopted from TIC++. */ #include <iostream> // head file for predefined io classes and objects #include <string> // head file for the predefined string class #include <vector>// head file for the predefined vector template using namespace std; class Pet { // define a class, group everything together, encapsulate as needed. protected: string name; // protected members can be accessed by child classes public: Pet() {name = “I have no name.";} // default constructor Pet(string nm){name = nm;} // constructor string getName() {return name;} // to be inherited by child classes //virtual method, to be overridden by child classes, for polymorphism virtual string speak() const { return “’I can't speak.’”; } }; Your second C++ Program

18. class Dog : public Pet { // inheritance public: Dog(){name = “I am a dog without a name.";} Dog(string nm){name = nm;} string speak() const { return "'bark! bark!'"; } }; class Cat : public Pet { public: Cat(){name = " I am a cat without a name.";} Cat(string nm){name = nm;} string speak() const { return "'meow! meow!'"; } }; Your second C++ Program

19. int main() { Dog d("Midnight"); Cat c("Ginger"); Pet p("Dummy"); cout << d.getName() << " says, " << d.speak() <<endl; cout << c.getName() << " says, " << c.speak() <<endl; cout << p.getName() << " says, " << p.speak() <<endl; cout << “We put all the pets together to make it easier to take care of them (code reuse). \n”; vector<Pet> pets; // “vector” mimics variable-size array, its type is a variable too (template) pets.push_back(d); pets.push_back(c); pets.push_back(p); for(int i=0; i<pets.size();i++) cout << "Pet " << i << " (" << pets[i].getName()<< ") " << " says " << pets[i].speak() << endl; cout << "The above did not work correctly. No one can speak now.\n”; cout << “Incorrect use of virtual methods for polymorphism. \n"; Your second C++ Program

20. cout << "The following do work correctly. \n”; cout << “Correct use of a virtual methodfor polymorphism. \n"; vector<Pet *> pets2; // pointer type pets2.push_back(&d); // taking address of d pets2.push_back(&c); pets2.push_back(&p); for(int i=0; i<pets2.size();i++) cout << "Pet " << i << " (" << pets2[i]->getName()<< ") " << " says " << pets2[i]->speak() << endl; cout << “Correct use of a virtual method for polymorphism. \n"; vector<Pet *> pets3; pets3.push_back(new Dog("Midnight2")); // a new dog created at run time pets3.push_back(new Cat("Ginger2")); pets3.push_back(new Pet("Dummy2")); for(int i=0; i<pets3.size();i++) cout << "Pet " << i << " (" << pets3[i]->getName()<< ") " << " says " << pets3[i]->speak() << endl; cout << "Please enter 'q' to quit.\n ";char a; cin >> a; } Your second C++ Program