B.sc CSIT 2nd semester C++ Unit4

Unit4 Operator overloading
Presented By : Tekendra Nath Yogi
Tekendranath@gmail.com
College Of Applied Business And Technology

Introduction
• C++ provides a rich collection of operators(e.g., +, -, /, *….etc). Such
operators are used with the fundamental types(int, float, char,…..etc).
– E.g., int a, b, c; a= b+c is perfectly valid
• But if we try to use these operators directly with user defined types (e.g.,
objects) compiler will produce error.
– E.g., if a, b, c are objects of user defined class then the statement a = b+c is
not valid
• So to use operators with objects we need to overload operators (i.e.,
Customizes the C++ operators for operands of user-defined types.).
– E,g, a= b+c can be made valid by using overloading.
2By: Tekendra Nath Yogi

Contd..
• What is operator overloading?
– The mechanism of giving special meanings to an operator is called
operator overloading.
– i.e., redefine the way operator behaves so that we can use them
with user-defined types.
– Although the semantics of an operator can be extended, we can not
change its syntax and semantics that govern its use such as the
number of operand, precedence and associativity.
• E.g., For example, the operator + should be overloaded for addition, not
subtraction.

Contd..
• Syntax:
– operator overloading is done with the help of special function, called the
operator function. The general form of operator function is as follows:

Contd..
• Example:
– To add two objects of type distance each having a data members feet of
type int and inches of type float, we can over load + operator as follows:

General rules(Restrictions) for operator overloading
• We can not invent new operators that do not exist in the
language.
• i.e., only existing operator in the language can be overloaded.
– E.g., @ is not a valid c++ operator and can not be overloaded

Contd..
• Overloaded operator must follow the same syntax:
– E.g., if x and y are objects of a user defined class then
• X++12; // not allowed: ++ is not a binary operator
• X++; is allowed
• %x ; is not allowed: % is not an unary operator
• Y= x%3; is allowed
• One can not change the number of operand used by the operator.
• Try to overload operator where they make sense.

Contd..
• We can not change the way an operator works between native
c++ types.
– E.g ., we can not change how works between a double and an integer
variable.
– But we can change the working of operator for user defined types.

Contd..
• We can not change the operator precedence rules.
• i.e., the order of operator evaluation remains unchanged.

Contd..
• We can not change the operator associativity rules.
– E.g., the unary minus(-) operator associates from right to left.
x= -y; // unary minus associates from right to left
x = y-; // we can not alter unary minus to go from left to right.

Contd..
• Overloading some operators does not implicitly define other
operators for us.
– E.g., overloading the + and = operators for a class does not mean that the
+= operator is overloaded automatically for us. We will need to write
overload code for the += operator as well.

Contd..
• The overloaded operator must have at least one operand that is of
user-defined type.
• When overloading an operator using a member function:
• The leftmost operand of the overloaded operator must be an object of
the class type.
• The leftmost operand becomes the implicit parameter. All other
operands become function parameter.

Contd..
• Almost any operator can be overloaded in C++. However there
are few operator which can not be overloaded. Operator that
are not overloaded are follows
– scope operator (::)
– sizeof
– member selector –(.)
– member pointer selector (.*)
– ternary operator (?:)

Overloading Unary operator
• The operators which acts upon only one operand are called unary
operators.
• The following is a list of unary operator that can be overloaded in c++:
– Unary minus(-)
– Unary plus(+)
– Ones complement(~)
– Pointer dereference(*)
– Not (!)
– Increment operator(++)
– Decrement operator(--)

Contd..
• Prefix(++, --) and postfix (++. --)unary operator overloading:
– Increment operators increase the value of operand by 1, while decrement
operators(--) decrease value of operand by 1.
– They can be written either before the operand or after it. Depending on its
location, they can be classified as either prefix operators or postfix
operators.
– If the increment and decrement operators are written before the operand,
then they are termed as prefix operators. However, if they are written after
the operand, then they are termed as postfix operators.

Contd..

Contd..
• Overloading prefix increment operator:

Contd..

Contd..
• Overloading prefix decrement operator:

Contd..

Contd..
• Class work: WAP to overload prefix operator as shown above use
parameterized constructor to initialize the value of data member
count.

Contd..
• Overload postfix increment operator:

Contd..

Contd..• Overload postfix decrement operator:

Contd..

• Returning values from operator function: Returning values using temporary
objects:

Contd..

Contd..
• Returning values using nameless temporary objects:

Contd..

Overloading Binary Operators
• Binary operator are operators, which require two operands to perform the
operation.
– Arithmetic operators(+, -, *, /, %)
– Assignment operator(= , +=, -=, /=, *=, %=)
– Comparison operator(>, <, <=, >=, ==, !=)
• Binary operators can be overloaded as unary operator however binary operator
requires an additional parameter.
• In overloading binary operators the object to the left of the operator is used to
invoke the operator function while the operand to the right of the operator is
always passed as an argument to the function.

Arithmetic operators overloading
• Overloading plus operator:
– This operator adds the values of two operands when applied to a basic
data item.
– This operator can be overloaded to add the values of corresponding data
members when applied to two objects.

Contd..

Contd..
• Note: in the same way we can overload other arithmetic
operators( -, *, /, %) to subtract, multiply, and divide objects.

Contd..
• Example: WAP to subtract one object from another object.

Contd..

Contd..
• Homework:
– Write a program to compute subtraction of two complex numbers using
– Write a program to compute addition of two complex numbers using
– WAP to multiply two objects.
– WAP to illustrate modulo and normal division of objects using operator
overloading.

Overloading comparison operator
• Comparison operator(>, <, <=, >=, ==, !=)
• Overloading comparison operator is almost similar to overloading arithmetic
operator except that it must return value of an integer type.
• This is because result of comparison is always true or false.

Contd..
• Overloading less than (<) operator:

Contd..
• Output:
Note: in the same way other
relational operators can be
overloaded.

Contd..
• Homework:
– Write a program that takes two amount (can be in RS and PS) as
input and decide which one is less.
– Write a program to compare the two distances taken as input in the
program and decide which one is greater than other.

Overloading assignment operator
• In c++ overloading of assignment(=) operator is possible.
• By overloading assignment operator, all values of one object can be
copied to another object by using assignment operator.
• Assignment operator must be overloaded by non-static member
function only.
• If the overloading function for the assignment operator is not written in
the class, the compiler generates the function to overload the
assignment operator.

Contd..

Contd..
• Similar to copy constructor overriding:
– if the members of the objects are pointers then during assignment only the
address are copied. That is, both of the objects point to the same memory
area and they don not have distinct data.
• The difference is:
– copy constructor initializes during object creation where as the assignment
operator assigns(copies) to the already created(well constructed) object.

Data Conversion(Type conversion)
• It is the process of converting one type into another. In other words converting an
expression of a given type into another is called type conversion.
• A type conversion may either be explicit or implicit, depending on whether it is
ordered by the programmer or by the compiler.
• Explicit type conversions are used when a programmer want to get around the
compiler’s typing system.
• If the data types are user defined, the compiler does not support automatic type
conversion and therefore, we must design the conversion routine by ourselves.

Contd..
• Four types of situations might arise in the data conversion:
– Basic to basic
– Basic to user-defined
– User-defined to basic
– User-defined to user-defined

Contd..
• Conversion from basic type to user defined type:
– To convert basic types to user defined type(object) it is necessary to use
the constructor.
– The constructor in this case takes single argument whose type is to be
converted.
– Syntax:

Contd..

Contd..
Output:

Contd..
• Conversion from user defined type to basic type:
– To convert user defined types(objects) to basic type it is necessary to
overload cast operator.
– The overloaded cast operator does not have return type. Its implicit return
type is the type to which object need to be converted.
– To convert object to basic type, we use conversion function as below:
– Syntax:

Contd..

Contd..
• Output:

Contd..
• Conversion from user defined type to another user defined type:
– C++ compiler does not support data conversion between objects of user-
defined classes.
– This type of conversion can be carried out either by:
• A One argument constructor or
• an operator function.
– The choice between these two methods for data conversion depends on
whether the conversion function be defined in the source class or
destination class.

Contd..
• Consider the example:
Class A objA;
ClassB objB;
//…………
objA= ObjB;
– Conversion function can be defined in classA(destination) or classB(source).
– If the conversion function is to be defined in classA, one argument
constructor is used or
– if the conversion function is to be defined in source the conversion operator
function should be used.

Contd..
• Routine in source class: The syntax of conversion from user-
defined to user –defined when conversion is specified in the
source class:

Contd..

Contd..
• Output:

Contd..
• Routine in destination class:
– In this case, it is necessary that the constructor be placed in the destination
class.
– This constructor is a single argument constructor and serves as instruction
for converting the argument’s type to the class type of which it is a
member.

Contd..
• Following is the syntax of conversion when conversion function
is in destination class:

Contd..

Homework
• What is operator overloading? What are the benefits of operator overloading
in C++? How is operator overloading different from function overloading.
• Which operators are not allowed to be overloaded? Why?
• What are the differences between overloading a unary operator and that of a
binary operator? Illustrate with suitable examples.
• What is difference between overloading a unary operator and that of a binary
operator? Illustrate with suitable examples.
• Write a program to convert polar co-ordinate into rectangular coordinate
using conversion/cast function.

Contd..
• Design a class Matrix of dimension 3x3. overload + operator to find sum of two materics.
• Write a program that decreases an integer value by 1 by overloading – - operator.
• Write a program that increases an integer value by 1 by overloading ++ operator.
• Write a program to find next element of Fibonacci series by overloading ++ operator.
• Why data conversion is needed? Write a program to convert kilogram into gram using user defined to
user defined data conversion.(1kg = 100gm).
• Write a program to convert an object of dollar class to object of rupees class. Assume that dollar class
has data members dol and cent an rupees class have data members rs and paisa.
• Write a program to convert object from class that represents temperature in Celsius scale to object of a
class that represents it in Fahrenheit scale.
• Write a program to convert object from a class that represents weight of gold in Nepal tola, to object of
a class that represents international gold measurement of weight in gram scale( 1 tola = 11.664 gram)

Thank You !

B.sc CSIT 2nd semester C++ Unit4

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B.sc CSIT 2nd semester C++ Unit4