Object Oriented Programming

1. Object Oriented Programming C++

2. ADT vs. Class • ADT: a model of data AND its related functions • C++ Class: a syntactical & programmatic element for describing how the functions and data are related • An ADT implementation has several parts: • interface function-names (methods) • operators (possibly re-defined symbols) • data • Any/all of these may be public or private

3. Classes • Collection of data elements and functions • Functions are called "methods" or members of the class • Tied to the data • May be hidden from other functions • Member access • exposed by "public" names • Hidden by "private" names

4. Classes - example classComplx {public: float my_real_part; float my_imag_part; }; // note the semicolon!!!!! • Using "public" makes all elements "visible" • Using "private", would make them visible ONLY to methods (functions) inside the class (not shown). • NOTE: looks a lot like a struct

5. Program structure – pt 2 - C++ • Usually, put the class definition in a header file • #include it later in BOTH : • the implementation file • where the methods are defined • the user-program file • where methods get used

6. Objects • An object is just a struct with members • Default operations (members) • Constructor • Destructor • Assignment • Copy • YOU must provide any initialization code • in a constructor • YOU must provide return values (if any) • YOU must free any dynamic storage

7. Constructors • C++ provides a "default" constructor • Only works if no parameters: Complx X; • Fails for uses like: Complx X(3,4); • variables get initialized • other setup must be done • IF you create a constructor, you MUST specify the Default Constructor too or it won't exist • Complx( ) { }; • no actual code needed inside the { }

8. Class Constructors • Assign initial values to an object • Never returns a value • Same name as the class • Guaranteed to be called (automatic) upon instantiation of an object of type class

9. Destructors • Automatically run when an object of type class goes out of scope • use to clean up after the object (return dynamically allocated storage to the storage management system • Same name as the class, but preceded by a ~ • no overloading allowed • never returns a value • not needed for statically allocated storage

10. C++ console I/O • basic operators • << the "insertion" operator • >> the "extraction" operator • stream names for standard I/O • cin is the input "file" • cout is the output "file" • usage • cin>>x; // get a value • cout<<x; // output a value

11. Operators • Ordinary variables have basic operators built-in + - * / % | & || && • New objects (structs, classes) may need more • How do you "add" 2 complex numbers? • Given: complex#'s a and b; • what does a+b mean??? • compiler knows nothing about complex #'s • Define a NEW action to perform "+" • but continue to use the "+" operator!!!! • add the real parts, add the imaginary parts • store each result in the proper answer-part.

12. Operators – 2 • Often, we "want" to re-use an operator • i.e.; give a new meaning to "+" • this is called "overloading" • let "+" mean "add complex numbers" as well as add integers, floats, etc. • c=a+b; // a, b & c are Complex • May need a "friend" function, due to flaws in the C++ object model • "friend" functions do not get the leading "classname::" syntax

13. More on Overloading • = overload this as a member function • == != <= >= <>overload as a non-member (friend function) returning a boolean • >> << (insertion and extraction) overload as non-members (friends) returning type iostream • + - * / %(arithmetic) as overload non-members • += and -=... overload same as + and - • cannot overload :: .sizeof ?:

14. Polymorphism (multiple forms) • x=sqrt(y); // what data type is "y"? • could be: float, int, double, real • How does compiler know how to handle the incoming data? • An object allows us to create MULTIPLE methods • all have the same name • all have different parameter types • compiler links caller's code & the "right one" based on parameter types. • Object writer creates these multiple methods

15. Operators • Ordinary variables have basic operators built-in + - * / % | & || && • New objects (structs, classes) may need more • How do you "add" 2 complex numbers? • Given: Complex#'s a and b; • what does a+b mean??? • compiler knows nothing about Complex #'s • Define a NEW action to perform "+" • add the real parts, add the imaginary parts • store each result in the proper answer-part.

16. Example – Declare the methods class Complx {private:// hidden member data float my_real_part, my_imag_part; // below are member functions (i.e.; "methods") public: Complx (float a, float b); // initializing constructor Complx( ) { }; // default constructor float get_real(Complx) { return my_real_part; } // not shown Complxoperator + (Complx); // defines "+" as a member name // define what output means friendstd::ostream&operator<<(std::ostream&xout, constComplx&C ) { xout<< C.my_real_part <<"+"<< C.my_imag_part<<"j"; return xout; // modifies meaning of “cout” } }; // orange: declare parts of the class, green: use it, red: return-value

17. Example- implementation // :: means the name after :: is a member of the class "Complx" Complx::Complx(float a, float b) // implement constructor {my_real_part=a; my_imag_part=b;} ComplxComplx::operator+ (ComplxC) {Complxtmp; // need a place for output tmp.my_real_part= my_real_part + C.my_real_part; tmp.my_imag_part= my_imag_part + C.my_imag_part; return tmp; } // orange: declare parts of the class, green: use it, red: return-value

18. "friend"s friendstd::ostream&operator<<(std::ostream&xout, constComplx&C ) { xout<< C.my_real_part <<"+"<< C.my_imag_part<<"j"; return xout; } • What does it do? • Remember that we needed to define + for complex numbers? • Now need to define how to output them • Output functions don't understand class data • So we have now overloaded: • the + operator • the << operator

19. "friend"s - pt-2 • Can access privateand protectedmembers • NOTa member of the class • Allows operations across multiple classes • <<is a member of the iostreamclass • Want << able to output private data in Complx

20. Example-pt 2 void main() { ComplxA(2,2); ComplxB(1,1), C; C=A+B; }