UNIT POLYMORPHISM

Transcription

1 UNIT POLYMORPHISM CONTENTS 3.1. ADT Conversions 3.2. Overloading 3.3. Overloading Operators 3.4. Unary Operator Overloading 3.5. Binary Operator Overloading 3.6. Function Selection 3.7. Pointer Operators 3.8. Visitation 3.9. Iterators Containers List List Iterators Objective Questions Key Term Quiz Review Questions 1

2 3.1. ADT Conversions Explicit type conversion of an expression is necessary when either the implicit conversions are not desired or the expression will not otherwise be legal. One aim of OOP using C++ is the integration of user-defined ADTs and built-in types. To achieve this, there is a mechanism for having a member function provide an explicit conversion. For example, we can convert from an already-defined type to a user-defined type: my_string::my_string(const char* p); This is automatically a type conversion from char* to my_string. It is available both explicitly and implicitly. Explicitly, it is used as a conversion operation in either cast or functional form. Thus, both of the following pieces of code work: my_string s; char* logo = "Geometrics Inc"; s = static_cast<my_string>(logo); and s = logo; //implicit invocation of conversion 3.2. Overloading i) C++ permits the use of two function with the same name. However such functions essentially have different argument list. The difference can be in terms of number or type of arguments or both. ii) This process of using two or more functions with the same name but differing in the signature is called function overloading. iii) But overloading of functions with different return types are not allowed. iv) In overloaded functions, the function call determines which function definition will be executed. v) The biggest advantage of overloading is that it helps us to perform same operations on different datatypes without having the need to use separate names for each version. #include<iostream> using namespace std; int abslt(int ); long abslt(long ); float abslt(float ); double abslt(double ); int main() { int intgr=-5; long lng=34225; float flt=-5.56; double dbl= ; 2

3 cout<<\" absoulte value of \"<<intgr<<\" = \"<<abslt(intgr)<<endl; cout<<\" absoulte value of \"<<lng<<\" = \"<<abslt(lng)<<endl; cout<<\" absoulte value of \"<<flt<<\" = \"<<abslt(flt)<<endl; cout<<\" absoulte value of \"<<dbl<<\" = \"<<abslt(dbl)<<endl; int abslt(int num) { if(num>=0) return num; else return (-num); long abslt(long num) { if(num>=0) return num; else return (-num); float abslt(float num) { if(num>=0) return num; else return (-num); double abslt(double num) { if(num>=0) return num; else return (-num); Overloading Operators When an operator is used for different operations, such process is called operator overloading. In C pointer operator * is used to declare pointer variable as well as it is used for multiplication expression. Similarly in C++ << is used display values of different data types without specifying any format code, like in C. The same operator is also used in bit wise operation. cout <<77.45; cout<< This is C++; It is a special mechanism which gives a special meaning to the operator by the user definition. When an operator is overloaded, none of its original meanings are lost. The general form of a member operator function is: ret-type class name:: operator #(arg_list) { //oprations Here ret-type -> type of an object # -> is a placeholder to place any operator. Arg-list -> none fro unary operator and one for binary operator. There are mainly four in operator overloading. What are the rules for operator overloading? I. Only existing operator overloading. II. The overloaded operator must have at least one operand that is of user-defined type. III. The semantics of an operator can be extended, but we cannot change its syntax.

4 IV. Overloaded operators follow the syntax rules of the original operators that cannot be overidedon. Restrictions on operator overloading We cannot alter the precedence of an operator. We cannot change the number of operands that an operator takes we can choose or ignore an operand. Except for the function call operator, operator functions cannot have default arguments. What are the operators cannot be overloaded? Why? The following operators cannot be overloaded.. -> member operator :: -> scope resolution operator.* -> member selection through pointer to member? -> conditional operator Size of and typeid -> named operators They take name, rather than a value, as their second operand and provide the primary means of referring to members. Allowing them to be overloaded would lead to subtleties Unary Operator Overloading A unary operator, whether prefix or postfix, can be defined by either a non static member function taking no arguments or a non member function taking one argument. for any prefix unary operator #,#aa can be interpreted as either aa.operator #( ) or operator #(aa).for any postfix unary operator #,aa# can be interpreted as either aa.operator #(int) to operator #(aa.int).for anycase,if they are defined, overload resolution determines which, if any, interpretation is used. For example class x { x*operator& ( ); / / prefix unary& / / (address of) x operator&(x); / /binary & (and) : : ; x operator (x, x); / / binary minus x operator (x); / / prefix unary minus #include<iostream.h> Program to find the complex numbers using unary operator overloading #include<conio.h> class complex { int a,b,c; public: complex(){ void getvalue() { cout<<"enter the Two Numbers:"; cin>>a>>b;

5 void operator++() { a=++a; b=++b; void operator--() { a=--a; b=--b; void display() { cout<<a<<"+\t"<<b<<"i"<<endl; ; void main() { clrscr(); complex obj; obj.getvalue(); obj++; cout<<"increment Complex Number\n"; obj.display(); obj--; cout<<"decrement Complex Number\n"; obj.display(); getch(); Output: Enter the two numbers: 3 6 Increment Complex Number 4 + 7i Decrement Complex Number 3 + 6i 3.5. Binary Operator Overloading A binary operator can be defined by either a non-static member function taking one argument or a non member function taking two arguments. For any binary operator #, aa#bb can be interpreted as either aa.operator # (bb) or operator #(aa, bb).if both are defined, overload resolution determine which, if any, interpretation is used. For example class x { public: Void operator +(int); / / member operator / / function * x (int); ; void operator +(x, x); / / non member operator / / function Program to add two complex numbers using binary operator overloading #include<iostream.h> #include<conio.h> 5

6 class complex { int a,b; public: void getvalue() { cout<<"enter the value of Complex Numbers a,b:"; cin>>a>>b; complex operator+(complex ob) { complex t; t.a=a+ob.a; t.b=b+ob.b; return(t); complex operator-(complex ob) { complex t; t.a=a-ob.a; t.b=b-ob.b; return(t); void display() { cout<<a<<"+"<<b<<"i"<<"\n"; ; void main() { clrscr(); complex obj1,obj2,result,result1; 6 obj1.getvalue(); obj2.getvalue(); result = obj1+obj2; result1=obj1-obj2; cout<<"input Values:\n"; obj1.display(); obj2.display(); cout<<"result:"; result.display(); result1.display(); getch(); Output: Enter the value of Complex Numbers a, b 4 5 Enter the value of Complex Numbers a, b 2 2 Input Values 4 + 5i 2 + 2i

7 Result 6 + 7i 2 + 3i comma operator: The comma operator is a binary operator. We can make an overloaded comma perform any operation we want. If we want the overloaded comma to perform in a fashion similar to its normal operation, then our version must discard the values of all operands except the right most. The right most value becomes the result of the comma operator Function Selection FUNCTION SELECTION The Overloaded meaning is selected by matching the argument list of the function call to the argument list of the function declaration. When an overloaded function is invoked, the compiler must have a selection algorithm with which to pick the appropriate function. The algorithm that accomplishes this depends on what type conversions are available. A best match must be unique. It must be best on at least one argument and as good as any other match on all other arguments. Overloaded function selection algorithm: 1. Use an exact matches if found. 2. Try standard type promotions 3. Try standard type conversions. 4. Try user-defined conversions. 5. Use a match to ellipsis if found. Standard promotions are better than other standard conversions. These are conversions from float to double, and from bool, char, short or enum to int. Standard conversions also include pointer conversions. An exact match is clearly best Pointer Operators Overloading > The > pointer operator, also called the class member access operator, is considered a unary operator when overloading. Its general usage is shown here: object->element; Here, object is the object that activates the call. The operator >() function must return a pointer to an object of the class that operator >() operates upon. The element must be some member accessible within the object. 7

8 The following program illustrates overloading the > by showing the equivalence between ob.i and ob >i when operator >() returns the this pointer: #include <iostream> using namespace std; class myclass { public: int i; myclass *operator->() {return this; ; int main() { myclass ob; ob->i = 10; // same as ob.i cout << ob.i << " " << ob->i; return 0; An operator >() function must be a member of the class upon which it works Visitation Container classes are used to hold a large number of individual items. The types STACK and VECT are two such container classes. Many of the operations on container classes involve the ability to visit individual elements conveniently. There are variety of techniques to perform visitation and the extraction of elements from a class. One technique is to create iterator whose function is to visit the elements of an object in a container class. The iterator navigates over the elements of the class. Using visitation as the theme, we can write code that anticipates using the container classes and iterator objects and algorithms found in the standard template library. Conventional programming uses the for statement as its preferred means of structuring iteration, especially when processing arrays. //visit each a[i] and do something for (i=0;i<size;i++) sum+ = a[i]; The for statement specifies a specific order of visitation and is controlled by an index i, which is visibly modified. The order of visitation and the index used are generally details of implementation that do not affect the computation. 8

9 3.9. Iterators Visitation of the elements of an aggregate is a fundamental operation. When the aggregate is a class, an elegant solution to providing visitation operations is to create a separate but related class, called an iterator class, whose function is to visit and retrieve elements from aggregate. Iterators: An iterator is an object that can iterate or navigate or traverse over elements in the containers that represent data structures. These elements may be the entire or just a portion of a STL container. It represents a certain position in a container. Interators are object that are, more or less, pointers. They give the ability to cycle through the contents of a container in much same way that we would use of a pointer to cycle through an array. Since iterators are pointers, we can increment and decrement them and also apply the *operator to them.iterators are declared using the iterator type defined by the various containers. Five types of iterators: The following are the five types of iterators: Iterator Random Access Bi-directional Forward Input Output Access Allowed Store and retrieve values. Elements may be accessed randomly. Store and retrieve values. Forward and Backward moving. Store and retrieve values. Forward moving only. Retrieve, but not store values. Forward moving only. Store, but not retrieve values. Forward moving only Containers STL: The STL is a complex piece of software engineering that uses some of C++ s most sophisticated features. It provides general purpose, templatized classes and functions that implement many popular and commonly used algorithms and data structures like vectors, stacks, queues and lists. It also defines various routines that access them. are the foundational items of STL? I. Containers The three foundational items of standard library are: II. Algorithms III. Iterators 9

10 Container: A class holding a collection of elements of some type is commonly called a container class, or simply a container. The container is objects that hold other objects, and there are several different types. Each container class defines a set of functions that may be applied to the container. Two types of container: There are two types of containers. I. Sequence container: It provides a linear access on the elements. For example vector Class. dequq class and list class are sequence containers. ii. Associative container: It allow efficient retrieval of values based on keys. For Example, map, multi map, set and multi set. Common functions can be used in container: I. insert ( ) used to insert element into both container. II. erase ( ) used to removes elements from both container. III. push_back ( ) used to add an element to the end in a sequence container. IV. push_front ( ) used to add an element to the beginning of a sequence container. V. pop_back ( ) which removes elements from the end of the sequence container. VI. pop_front ( ) which removes elements from the start of the sequence container. VII. begin ( ) and end ( ) which returns iterators to start and end of the both container. VIII. find ( ) which is used to locate an element in an associative container given its key List List and its template: A list is a bi-directional linear list, which can be accessed sequentially only. A list has this template specification template <class T, class Allocator=allocator<T>> class list Here, T is the type of data stored into in the list. The allocator is specified by allocator which defaults to the standard allocator. constructors of a list: The list has the following constructors: explicit list (const Allocator &a, Allocator ( )); explicit list (size_type num, const T &val =T ( ), const Allocator 7a Allocator ( )); list (const list <T, Allocator > &ob); template <class InIter>list (InIter start,initer end,const Allocator &a =Allocator ( )); The first form constructs an empty list. The second form constructs a list that has num elements with the value val, which can be allowed to be default. The third form constructs a list that contains the same elements as ob.the fourth from constructs a list that contains the elements the in the range specified by the iterators start and end. Differentiate vector and list. Vector i). It has random-access. ii). It is created using dynamic allocation method. List i. It has sequential access. ii. It is created statically. 10

11 iii). Insertions and deletions are trade away iv). The accessing speed is very high v). It is uni-directional list. iii.the Insertions and deletion are low-cost iv. The accessing speed is very low. v. It is bi-directional list List Iterators. Example 1: // an iterator, a list container simple example #include <iostream> #include <list> using namespace std; int main() { // lst, list container for character elements list<char> lst; // append elements from 'A' to 'Z' to the list lst container for(char chs='a'; chs<='z'; ++chs) lst.push_back(chs); // iterate over all elements and print, separated by space list<char>::const_iterator pos; for(pos = lst.begin(); pos!= lst.end(); ++pos) cout<<*pos<<' '; cout<<endl; return 0; Example 2: // list_begin.cpp // compile with: /EHsc #include <list> #include <iostream> int main( ) { using namespace std; list <int> c1; list <int>::iterator c1_iter; list <int>::const_iterator c1_citer; c1.push_back( 1 ); c1.push_back( 2 ); c1_iter = c1.begin( ); cout << "The first element of c1 is " << *c1_iter << endl; *c1_iter = 20; c1_iter = c1.begin( ); cout << "The first element of c1 is now " << *c1_iter << endl; // The following line would be an error because iterator is const // *c1_citer = 200; 11

12 Friend Function Friend Function: A friend function is used for accessing the non-public members of a class. A class can allow nonmember functions and other classes to access its own private data, by making them friends. Thus, a friend function is an ordinary function or a member of another class. Defining Friend Function in C++: The friend function is written as any other normal function, except the function declaration of these functions is preceded with the keyword friend. The friend function must have the class to which it is declared as friend passed to it in argument. Some important points to note while using friend functions in C++: The keyword friend is placed only in the function declaration of the friend function and not in the function definition. It is possible to declare a function as friend in any number of classes. When a class is declared as a friend, the friend class has access to the private data of the class that made this a friend. A friend function, even though it is not a member function, would have the rights to access the private members of the class. It is possible to declare the friend function as either private or public. The function can be invoked without the use of an object. The friend function has its argument as objects, seen in example below. Example: To find the mean value of a given number using friend function. #include<iostream.h> #include<conio.h> class base { int val1,val2; public: void get() { cout<<"enter two values:"; cin>>val1>>val2; friend float mean(base ob); ; float mean(base ob) { return float(ob.val1+ob.val2)/2; void main() { clrscr(); base obj; obj.get(); cout<<"\n Mean value is : "<<mean(obj); getch(); 12

13 There are two methods by which operators can be overloaded, one using the member function and the other by using friend functions. Binary Operator overloading using friend function: Example: // Using friend functions to overload addition and subtraction operators #include <iostream.h> class myclass { int a; int b; public: myclass(){ myclass(int x,int y){a=x;b=y; void show() { cout<<a<<endl<<b<<endl; // these are friend operator functions // NOTE: Both the operands will be passed explicitly. // operand to the left of the operator will be passed as the first argument and operand to the right as the second argument friend myclass operator+(myclass,myclass); friend myclass operator-(myclass,myclass); ; myclass operator+(myclass ob1,myclass ob2) { myclass temp; temp.a = ob1.a + ob2.a; temp.b = ob1.b + ob2.b; return temp; myclass operator-(myclass ob1,myclass ob2) { myclass temp; temp.a = ob1.a - ob2.a; temp.b = ob1.b - ob2.b; return temp; void main() { myclass a(10,20); myclass b(100,200); a=a+b; a.show(); a=a-b; a.show(); Unary Operator overloading using friend function: Example: #include<iostream.h> #include<conio.h> class complex { 13

14 int a,b,c; public: complex(){ void getvalue() { cout<<"enter the Two Numbers:"; cin>>a>>b; void display() { cout<<a<<"+\t"<<b<<"i"<<endl; friend void operator++(); friend void operator--(); ; void operator++() { a=++a; b=++b; void operator--() { a=--a; b=--b; void main() { clrscr(); complex obj; obj.getvalue(); obj++; cout<<"increment Complex Number\n"; obj.display(); obj--; cout<<"decrement Complex Number\n"; obj.display(); getch(); Objective Questions 1. This process of using two or more functions with the same name but differing in the signature is called. a) Function overloading b)overloading c)operator overloading d) none 2. The keyword is also used to overload the built-in C++ operators. a) Overload b) operator c) both d) none 3. is one of the technique to perform visitation. a) b) c)iteration d) 4. Containers should designate a an member returning an iterator. a) Begin() b)end() c)both d) none 14

15 5. When a unary operator is overloaded using a member function, it has an argument list because the single operator argument is the implicit argument. a) empty b)single c)double d) single (or) double Key Term Quiz Key Terms: ( Container, list, STL, Iterators, visitation) Key Term Quiz: 1. A class holding a collection of elements of some type is commonly called a container class, or simply a. 2. A is a bi-directional linear list, which can be accessed sequentially only. 3. provides general purpose, templatized classes and functions that implement many popular and commonly used algorithms and data structures like vectors, stacks, queues and lists. 4. are either pointers or pointer-like objects. 5. Using as the theme, we can write code that anticipates using the container classes and iterator objects and algorithms found in the standard template library Review Questions PART A (2 Marks) 1. List the operations cannot used in overloading. 2. What is an iterator? What are its characteristics? 3. When you overload member function in what ways must they differ? 4. Define polymorphism. 5. Define binary operator. 6. Define Unary operator. 7. What are the rules for operator overloading? 8. What is meant by overloading? PART B (16 Marks) 1. Explain the operator overloading of Binary Operators in c++ with suitable example. 2. What is meant by function overloading? Write the rules associated with function overloading. Give suitable example to support your answer. 3. Consider two classes Employee, Manager with id and basic pay as data members and input and output member functions to get details and display tax. Write a friend function income tax to operate on the objects of both thses classes to calculate tax. 15

16 4. Write a inline function to find square of a number. 5. Write a program to overload + operator to add two Matrix objects and store results in another object. 6. Design a class Complex No. Using Operator Overloading wrire the routines to implement the operations add, sub, mul and div. 7. Design a class List and enumerate its member functions with the implementation of any three of them. 8. How will you overload unary and binary operators using friend functions? Explain with sample code. 9. (i) List out the operators that cannot be overloaded using friend function. (ii) What is meant by casting operator? Write the general form of overloaded casting operator. (iii) Write at least four rules for operator overloading. 16