Object Oriented Programming C++

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 2

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 3

Classes - example class Complx {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 4

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 5

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 6

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 { } 7

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

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

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 10

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. 11

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 12

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 ?:

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 ADT 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 14

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. 15

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 Complx get_real(return my_real_part); // not shown Complx operator + (Complx); // defines "+" as a member name // define what output means friend ostream &operator<<(ostream &xout, const Complx &C ) { xout << C.my_real_part <<"+"<< C.my_imag_part<<"j"; return output; } }; // orange: declare parts of the class, green: use it, red: return-value 16

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;} Complx Complx ::operator+ (Complx C) {Complx tmp; // 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 17

"friend"s friend ostream &operator<<(ostream &xout, const Complx &C ) { xout << C.my_real_part <<"+"<< C.my_imag_part<<"j"; return output; } 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 18

"friend"s - pt-2 Access private and protected members NOT a member of the class Allows operations across multiple classes << is a member of the iostream class Want << able to output private data in Complx 19

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