R Assignment Operators In C++

Operators in C++


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An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations. C++ is rich in built-in operators and provide the following types of operators −

  • Arithmetic Operators
  • Relational Operators
  • Logical Operators
  • Bitwise Operators
  • Assignment Operators
  • Misc Operators

This chapter will examine the arithmetic, relational, logical, bitwise, assignment and other operators one by one.

Arithmetic Operators

There are following arithmetic operators supported by C++ language −

Assume variable A holds 10 and variable B holds 20, then −

Show Examples

OperatorDescriptionExample
+Adds two operandsA + B will give 30
-Subtracts second operand from the firstA - B will give -10
*Multiplies both operandsA * B will give 200
/Divides numerator by de-numeratorB / A will give 2
%Modulus Operator and remainder of after an integer divisionB % A will give 0
++Increment operator, increases integer value by oneA++ will give 11
--Decrement operator, decreases integer value by oneA-- will give 9

Relational Operators

There are following relational operators supported by C++ language

Assume variable A holds 10 and variable B holds 20, then −

Show Examples

OperatorDescriptionExample
==Checks if the values of two operands are equal or not, if yes then condition becomes true.(A == B) is not true.
!=Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.(A != B) is true.
>Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.(A > B) is not true.
<Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.(A < B) is true.
>=Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.(A >= B) is not true.
<=Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.(A <= B) is true.

Logical Operators

There are following logical operators supported by C++ language.

Assume variable A holds 1 and variable B holds 0, then −

Show Examples

OperatorDescriptionExample
&&Called Logical AND operator. If both the operands are non-zero, then condition becomes true.(A && B) is false.
||Called Logical OR Operator. If any of the two operands is non-zero, then condition becomes true.(A || B) is true.
!Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true, then Logical NOT operator will make false.!(A && B) is true.

Bitwise Operators

Bitwise operator works on bits and perform bit-by-bit operation. The truth tables for &, |, and ^ are as follows −

pqp & qp | qp ^ q
00000
01011
11110
10011

Assume if A = 60; and B = 13; now in binary format they will be as follows −

A = 0011 1100

B = 0000 1101

-----------------

A&B = 0000 1100

A|B = 0011 1101

A^B = 0011 0001

~A  = 1100 0011

The Bitwise operators supported by C++ language are listed in the following table. Assume variable A holds 60 and variable B holds 13, then −

Show Examples

OperatorDescriptionExample
&Binary AND Operator copies a bit to the result if it exists in both operands. (A & B) will give 12 which is 0000 1100
|Binary OR Operator copies a bit if it exists in either operand.(A | B) will give 61 which is 0011 1101
^Binary XOR Operator copies the bit if it is set in one operand but not both.(A ^ B) will give 49 which is 0011 0001
~Binary Ones Complement Operator is unary and has the effect of 'flipping' bits. (~A ) will give -61 which is 1100 0011 in 2's complement form due to a signed binary number.
<<Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand.A << 2 will give 240 which is 1111 0000
>>Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand.A >> 2 will give 15 which is 0000 1111

Assignment Operators

There are following assignment operators supported by C++ language −

Show Examples

OperatorDescriptionExample
=Simple assignment operator, Assigns values from right side operands to left side operand.C = A + B will assign value of A + B into C
+=Add AND assignment operator, It adds right operand to the left operand and assign the result to left operand.C += A is equivalent to C = C + A
-=Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operand.C -= A is equivalent to C = C - A
*=Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operand.C *= A is equivalent to C = C * A
/=Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operand.C /= A is equivalent to C = C / A
%=Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operand.C %= A is equivalent to C = C % A
<<=Left shift AND assignment operator.C <<= 2 is same as C = C << 2
>>=Right shift AND assignment operator.C >>= 2 is same as C = C >> 2
&=Bitwise AND assignment operator.C &= 2 is same as C = C & 2
^=Bitwise exclusive OR and assignment operator.C ^= 2 is same as C = C ^ 2
|=Bitwise inclusive OR and assignment operator.C |= 2 is same as C = C | 2

Misc Operators

The following table lists some other operators that C++ supports.

Sr.NoOperator & Description
1

sizeof

sizeof operator returns the size of a variable. For example, sizeof(a), where ‘a’ is integer, and will return 4.

2

Condition ? X : Y

Conditional operator (?). If Condition is true then it returns value of X otherwise returns value of Y.

3

,

Comma operator causes a sequence of operations to be performed. The value of the entire comma expression is the value of the last expression of the comma-separated list.

4

. (dot) and -> (arrow)

Member operators are used to reference individual members of classes, structures, and unions.

5

Cast

Casting operators convert one data type to another. For example, int(2.2000) would return 2.

6

&

Pointer operator & returns the address of a variable. For example &a; will give actual address of the variable.

7

*

Pointer operator * is pointer to a variable. For example *var; will pointer to a variable var.

Operators Precedence in C++

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator −

For example x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator * has higher precedence than +, so it first gets multiplied with 3*2 and then adds into 7.

Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.

Show Examples

Category Operator Associativity 
Postfix () [] -> . ++ - -  Left to right 
Unary + - ! ~ ++ - - (type)* & sizeof Right to left 
Multiplicative  * / % Left to right 
Additive  + - Left to right 
Shift  << >> Left to right 
Relational  < <= > >= Left to right 
Equality  == != Left to right 
Bitwise AND Left to right 
Bitwise XOR Left to right 
Bitwise OR Left to right 
Logical AND && Left to right 
Logical OR || Left to right 
Conditional ?: Right to left 
Assignment = += -= *= /= %=>>= <<= &= ^= |= Right to left 
Comma Left to right 

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Assignment operators modify the value of the object.

Operator name Syntax Over​load​able Prototype examples (for class T)
Inside class definition Outside class definition
simple assignment Yes T& T::operator=(const T2& b);N/A
addition assignment Yes T& T::operator+=(const T2& b);T& operator +=(T& a, const T2& b);
subtraction assignment Yes T& T::operator-=(const T2& b);T& operator -=(T& a, const T2& b);
multiplication assignment Yes T& T::operator*=(const T2& b);T& operator *=(T& a, const T2& b);
division assignment Yes T& T::operator/=(const T2& b);T& operator /=(T& a, const T2& b);
modulo assignment Yes T& T::operator%=(const T2& b);T& operator %=(T& a, const T2& b);
bitwise AND assignment Yes T& T::operator&=(const T2& b);T& operator &=(T& a, const T2& b);
bitwise OR assignment Yes T& T::operator|=(const T2& b);T& operator |=(T& a, const T2& b);
bitwise XOR assignment Yes T& T::operator^=(const T2& b);T& operator ^=(T& a, const T2& b);
bitwise left shift assignment Yes T& T::operator<<=(const T2& b);T& operator <<=(T& a, const T2& b);
bitwise right shift assignment Yes T& T::operator>>=(const T2& b);T& operator >>=(T& a, const T2& b);
Notes
  • All built-in assignment operators return *this, and most user-defined overloads also return *this so that the user-defined operators can be used in the same manner as the built-ins. However, in a user-defined operator overload, any type can be used as return type (including void).
  • can be any type including

[edit]Explanation

copy assignment operator replaces the contents of the object with a copy of the contents of ( is not modified). For class types, this is a special member function, described in copy assignment operator.

move assignment operator replaces the contents of the object with the contents of , avoiding copying if possible ( may be modified). For class types, this is a special member function, described in move assignment operator. (since C++11)

For non-class types, copy and move assignment are indistinguishable and are referred to as direct assignment.

compound assignment operators replace the contents of the object with the result of a binary operation between the previous value of and the value of .

[edit]Builtin direct assignment

The direct assignment expressions have the form

lhsrhs (1)
lhs = {} (2) (since C++11)
lhs = {rhs} (3) (since C++11)

For the built-in operator, lhs may have any non-const scalar type and rhs must be implicitly convertible to the type of lhs.

The direct assignment operator expects a modifiable lvalue as its left operand and an rvalue expression or a braced-init-list(since C++11) as its right operand, and returns an lvalue identifying the left operand after modification.

For non-class types, the right operand is first implicitly converted to the cv-unqualified type of the left operand, and then its value is copied into the object identified by left operand.

When the left operand has reference type, the assignment operator modifies the referred-to object.

If the left and the right operands identify overlapping objects, the behavior is undefined (unless the overlap is exact and the type is the same)

If the right operand is a braced-init-list

  • if the expression has scalar type,
  • the expression E1 ={} is equivalent to E1 = T{}, where is the type of .
  • the expression E1 ={E2} is equivalent to E1 = T{E2}, where is the type of .
  • if the expression has class type, the syntax E1 ={args...} generates a call to the assignment operator with the braced-init-list as the argument, which then selects the appropriate assignment operator following the rules of overload resolution. Note that, if a non-template assignment operator from some non-class type is available, it is preferred over the copy/move assignment in because to non-class is an identity conversion, which outranks the user-defined conversion from to a class type.
(since C++11)

In overload resolution against user-defined operators, for every type , the following function signatures participate in overload resolution:

T*& operator=(T*&, T*);

T*volatile& operator=(T*volatile&, T*);

For every enumeration or pointer to member type , optionally volatile-qualified, the following function signature participates in overload resolution:

T& operator=(T&, T );

For every pair A1 and A2, where A1 is an arithmetic type (optionally volatile-qualified) and A2 is a promoted arithmetic type, the following function signature participates in overload resolution:

A1& operator=(A1&, A2);

[edit]Example

Run this code

Output:

#include <iostream>int main(){int n =0;// not an assignment n =1;// direct assignmentstd::cout<< n <<' '; n ={};// zero-initialization, then assignmentstd::cout<< n <<' '; n ='a';// integral promotion, then assignmentstd::cout<< n <<' '; n ={'b'};// explicit cast, then assignmentstd::cout<< n <<' '; n =1.0;// floating-point conversion, then assignmentstd::cout<< n <<' ';// n = {1.0}; // compiler error (narrowing conversion)   int& r = n;// not an assignmentint* p;   r =2;// assignment through referencestd::cout<< n <<'\n'; p =&n;// direct assignment p = nullptr;// null-pointer conversion, then assignment   struct{int a;std::string s;} obj; obj ={1, "abc"};// assignment from a braced-init-liststd::cout<< obj.a<<':'<< obj.s<<'\n';}

[edit]Builtin compound assignment

The compound assignment expressions have the form

lhsoprhs (1)
lhs op {} (2) (since C++11)
lhs op {rhs} (3) (since C++11)
op - one of *=, /=%=, +=-=, <<=, >>=, &=, ^=, |=
lhs - for the built-in operator, lhs may have any arithmetic type, except when op is += or -=, which also accept pointer types with the same restrictions as + and -
rhs - for the built-in operator, rhs must be implicitly convertible to lhs

The behavior of every builtin compound-assignment expression E1 op= E2 (where E1 is a modifiable lvalue expression and E2 is an rvalue expression or a braced-init-list(since C++11)) is exactly the same as the behavior of the expression E1 = E1 op E2, except that the expression is evaluated only once and that it behaves as a single operation with respect to indeterminately-sequenced function calls (e.g. in f(a += b, g()), the += is either not started at all or is completed as seen from inside g()).

In overload resolution against user-defined operators, for every pair A1 and A2, where A1 is an arithmetic type (optionally volatile-qualified) and A2 is a promoted arithmetic type, the following function signatures participate in overload resolution:

A1& operator*=(A1&, A2);

A1& operator/=(A1&, A2);

A1& operator+=(A1&, A2);

A1& operator-=(A1&, A2);

For every pair I1 and I2, where I1 is an integral type (optionally volatile-qualified) and I2 is a promoted integral type, the following function signatures participate in overload resolution:

I1& operator%=(I1&, I2);

I1& operator<<=(I1&, I2);

I1& operator>>=(I1&, I2);

I1& operator&=(I1&, I2);

I1& operator^=(I1&, I2);

I1& operator|=(I1&, I2);

For every optionally cv-qualified object type , the following function signatures participate in overload resolution:

[edit]Example

[edit]See also

Operator precedence

Operator overloading

Common operators
assignment increment
decrement
arithmetic logical comparison member
access
other

a = b
a += b
a -= b
a *= b
a /= b
a %= b
a &= b
a |= b
a ^= b
a <<= b
a >>= b

++a
--a
a++
a--

+a
-a
a + b
a - b
a * b
a / b
a % b
~a
a & b
a | b
a ^ b
a << b
a >> b

!a
a && b
a || b

a == b
a != b
a < b
a > b
a <= b
a >= b
a <=> b

a[b]
*a
&a
a->b
a.b
a->*b
a.*b

a(...)
a, b
?:

Special operators

converts one type to another related type
converts within inheritance hierarchies
adds or removes cv qualifiers
converts type to unrelated type
C-style cast converts one type to another by a mix of , , and
creates objects with dynamic storage duration
destructs objects previously created by the new expression and releases obtained memory area
queries the size of a type
queries the size of a parameter pack(since C++11)
queries the type information of a type
checks if an expression can throw an exception (since C++11)
queries alignment requirements of a type (since C++11)

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