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C Assignment Operators

Summary : in this tutorial, you’ll learn about the C assignment operators and how to use them effectively.

Introduction to the C assignment operators

An assignment operator assigns the vale of the right-hand operand to the left-hand operand. The following example uses the assignment operator (=) to assign 1 to the counter variable:

After the assignmment, the counter variable holds the number 1.

The following example adds 1 to the counter and assign the result to the counter:

The = assignment operator is called a simple assignment operator. It assigns the value of the left operand to the right operand.

Besides the simple assignment operator, C supports compound assignment operators. A compound assignment operator performs the operation specified by the additional operator and then assigns the result to the left operand.

The following example uses a compound-assignment operator (+=):

The expression:

is equivalent to the following expression:

The following table illustrates the compound-assignment operators in C:

• A simple assignment operator assigns the value of the left operand to the right operand.
• A compound assignment operator performs the operation specified by the additional operator and then assigns the result to the left operand.

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Assignment Operators in C

In C language, the assignment operator stores a certain value in an already declared variable. A variable in C can be assigned the value in the form of a literal, another variable, or an expression.

The value to be assigned forms the right-hand operand, whereas the variable to be assigned should be the operand to the left of the " = " symbol, which is defined as a simple assignment operator in C.

In addition, C has several augmented assignment operators.

The following table lists the assignment operators supported by the C language −

Simple Assignment Operator (=)

The = operator is one of the most frequently used operators in C. As per the ANSI C standard, all the variables must be declared in the beginning. Variable declaration after the first processing statement is not allowed.

You can declare a variable to be assigned a value later in the code, or you can initialize it at the time of declaration.

You can use a literal, another variable, or an expression in the assignment statement.

Once a variable of a certain type is declared, it cannot be assigned a value of any other type. In such a case the C compiler reports a type mismatch error.

In C, the expressions that refer to a memory location are called "lvalue" expressions. A lvalue may appear as either the left-hand or right-hand side of an assignment.

On the other hand, the term rvalue refers to a data value that is stored at some address in memory. A rvalue is an expression that cannot have a value assigned to it which means an rvalue may appear on the right-hand side but not on the left-hand side of an assignment.

Variables are lvalues and so they may appear on the left-hand side of an assignment. Numeric literals are rvalues and so they may not be assigned and cannot appear on the left-hand side. Take a look at the following valid and invalid statements −

Augmented Assignment Operators

In addition to the = operator, C allows you to combine arithmetic and bitwise operators with the = symbol to form augmented or compound assignment operator. The augmented operators offer a convenient shortcut for combining arithmetic or bitwise operation with assignment.

For example, the expression "a += b" has the same effect of performing "a + b" first and then assigning the result back to the variable "a".

Run the code and check its output −

Similarly, the expression "a <<= b" has the same effect of performing "a << b" first and then assigning the result back to the variable "a".

Here is a C program that demonstrates the use of assignment operators in C −

When you compile and execute the above program, it will produce the following result −

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In C programming, a struct (or structure) is a collection of variables (can be of different types) under a single name.

• Define Structures

Before you can create structure variables, you need to define its data type. To define a struct, the struct keyword is used.

Syntax of struct

For example,

Here, a derived type struct Person is defined. Now, you can create variables of this type.

Create struct Variables

When a struct type is declared, no storage or memory is allocated. To allocate memory of a given structure type and work with it, we need to create variables.

Here's how we create structure variables:

Another way of creating a struct variable is:

In both cases,

• person1 and person2 are struct Person variables
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There are two types of operators used for accessing members of a structure.

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Suppose, you want to access the salary of person2 . Here's how you can do it.

Example 1: C structs

In this program, we have created a struct named Person . We have also created a variable of Person named person1 .

In main() , we have assigned values to the variables defined in Person for the person1 object.

Notice that we have used strcpy() function to assign the value to person1.name .

This is because name is a char array ( C-string ) and we cannot use the assignment operator = with it after we have declared the string.

Finally, we printed the data of person1 .

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We use the typedef keyword to create an alias name for data types. It is commonly used with structures to simplify the syntax of declaring variables.

For example, let us look at the following code:

We can use typedef to write an equivalent code with a simplified syntax:

Example 2: C typedef

Here, we have used typedef with the Person structure to create an alias person .

Now, we can simply declare a Person variable using the person alias:

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You can create structures within a structure in C programming. For example,

Suppose, you want to set imag of num2 variable to 11 . Here's how you can do it:

Example 3: C Nested Structures

Why structs in c.

Suppose you want to store information about a person: his/her name, citizenship number, and salary. You can create different variables name , citNo and salary to store this information.

What if you need to store information of more than one person? Now, you need to create different variables for each information per person: name1 , citNo1 , salary1 , name2 , citNo2 , salary2 , etc.

A better approach would be to have a collection of all related information under a single name Person structure and use it for every person.

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Assignment and shorthand assignment operator in C

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• Shorthand assignment

Assignment operator is used to assign value to a variable (memory location). There is a single assignment operator = in C. It evaluates expression on right side of = symbol and assigns evaluated value to left side the variable.

For example consider the below assignment table.

The RHS of assignment operator must be a constant, expression or variable. Whereas LHS must be a variable (valid memory location).

Shorthand assignment operator

C supports a short variant of assignment operator called compound assignment or shorthand assignment. Shorthand assignment operator combines one of the arithmetic or bitwise operators with assignment operator.

For example, consider following C statements.

The above expression a = a + 2 is equivalent to a += 2 .

Similarly, there are many shorthand assignment operators. Below is a list of shorthand assignment operators in C.

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C Assignment Operators

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An assignment operation assigns the value of the right-hand operand to the storage location named by the left-hand operand. Therefore, the left-hand operand of an assignment operation must be a modifiable l-value. After the assignment, an assignment expression has the value of the left operand but isn't an l-value.

assignment-expression :   conditional-expression   unary-expression assignment-operator assignment-expression

assignment-operator : one of   = *= /= %= += -= <<= >>= &= ^= |=

The assignment operators in C can both transform and assign values in a single operation. C provides the following assignment operators:

In assignment, the type of the right-hand value is converted to the type of the left-hand value, and the value is stored in the left operand after the assignment has taken place. The left operand must not be an array, a function, or a constant. The specific conversion path, which depends on the two types, is outlined in detail in Type Conversions .

• Assignment Operators

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1. Simple Assignment Operator (=)

Example of simple assignment operator.

2. Compound Assignment Operators

Example of Augmented Arithmetic and Assignment Operators

Example of Augmented Bitwise and Assignment Operators

Practice problems on assignment operators in c, 1. what will the value of "x" be after the execution of the following code, 2. after executing the following code, what is the value of the number variable, benefits of using assignment operators, best practices and tips for using the assignment operator, live classes schedule.

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Next: Unions , Previous: Overlaying Structures , Up: Structures   [ Contents ][ Index ]

15.13 Structure Assignment

Assignment operating on a structure type copies the structure. The left and right operands must have the same type. Here is an example:

Notionally, assignment on a structure type works by copying each of the fields. Thus, if any of the fields has the const qualifier, that structure type does not allow assignment:

See Assignment Expressions .

When a structure type has a field which is an array, as here,

structure assigment such as r1 = r2 copies array fields’ contents just as it copies all the other fields.

This is the only way in C that you can operate on the whole contents of a array with one operation: when the array is contained in a struct . You can’t copy the contents of the data field as an array, because

would convert the array objects (as always) to pointers to the zeroth elements of the arrays (of type struct record * ), and the assignment would be invalid because the left operand is not an lvalue.

21.12 — Overloading the assignment operator

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Operator overloading.

Customizes the C++ operators for operands of user-defined types.

[ edit ] Syntax

Overloaded operators are functions with special function names:

[ edit ] Overloaded operators

When an operator appears in an expression , and at least one of its operands has a class type or an enumeration type , then overload resolution is used to determine the user-defined function to be called among all the functions whose signatures match the following:

Note: for overloading co_await , (since C++20) user-defined conversion functions , user-defined literals , allocation and deallocation see their respective articles.

Overloaded operators (but not the built-in operators) can be called using function notation:

[ edit ] Restrictions

• The operators :: (scope resolution), . (member access), .* (member access through pointer to member), and ?: (ternary conditional) cannot be overloaded.
• New operators such as ** , <> , or &| cannot be created.
• It is not possible to change the precedence, grouping, or number of operands of operators.
• The overload of operator -> must either return a raw pointer, or return an object (by reference or by value) for which operator -> is in turn overloaded.
• The overloads of operators && and || lose short-circuit evaluation.

[ edit ] Canonical implementations

Besides the restrictions above, the language puts no other constraints on what the overloaded operators do, or on the return type (it does not participate in overload resolution), but in general, overloaded operators are expected to behave as similar as possible to the built-in operators: operator + is expected to add, rather than multiply its arguments, operator = is expected to assign, etc. The related operators are expected to behave similarly ( operator + and operator + = do the same addition-like operation). The return types are limited by the expressions in which the operator is expected to be used: for example, assignment operators return by reference to make it possible to write a = b = c = d , because the built-in operators allow that.

Commonly overloaded operators have the following typical, canonical forms: [1]

[ edit ] Assignment operator

The assignment operator ( operator = ) has special properties: see copy assignment and move assignment for details.

The canonical copy-assignment operator is expected to be safe on self-assignment , and to return the lhs by reference:

In those situations where copy assignment cannot benefit from resource reuse (it does not manage a heap-allocated array and does not have a (possibly transitive) member that does, such as a member std::vector or std::string ), there is a popular convenient shorthand: the copy-and-swap assignment operator, which takes its parameter by value (thus working as both copy- and move-assignment depending on the value category of the argument), swaps with the parameter, and lets the destructor clean it up.

This form automatically provides strong exception guarantee , but prohibits resource reuse.

[ edit ] Stream extraction and insertion

The overloads of operator>> and operator<< that take a std:: istream & or std:: ostream & as the left hand argument are known as insertion and extraction operators. Since they take the user-defined type as the right argument ( b in a @ b ), they must be implemented as non-members.

These operators are sometimes implemented as friend functions .

[ edit ] Function call operator

When a user-defined class overloads the function call operator, operator ( ) , it becomes a FunctionObject type.

An object of such a type can be used in a function call expression:

Many standard algorithms, from std:: sort to std:: accumulate accept FunctionObject s to customize behavior. There are no particularly notable canonical forms of operator ( ) , but to illustrate the usage:

[ edit ] Increment and decrement

When the postfix increment or decrement operator appears in an expression, the corresponding user-defined function ( operator ++ or operator -- ) is called with an integer argument 0 . Typically, it is implemented as T operator ++ ( int ) or T operator -- ( int ) , where the argument is ignored. The postfix increment and decrement operators are usually implemented in terms of the prefix versions:

Although the canonical implementations of the prefix increment and decrement operators return by reference, as with any operator overload, the return type is user-defined; for example the overloads of these operators for std::atomic return by value.

[ edit ] Binary arithmetic operators

Binary operators are typically implemented as non-members to maintain symmetry (for example, when adding a complex number and an integer, if operator+ is a member function of the complex type, then only complex + integer would compile, and not integer + complex ). Since for every binary arithmetic operator there exists a corresponding compound assignment operator, canonical forms of binary operators are implemented in terms of their compound assignments:

[ edit ] Comparison operators

Standard algorithms such as std:: sort and containers such as std:: set expect operator < to be defined, by default, for the user-provided types, and expect it to implement strict weak ordering (thus satisfying the Compare requirements). An idiomatic way to implement strict weak ordering for a structure is to use lexicographical comparison provided by std::tie :

Typically, once operator < is provided, the other relational operators are implemented in terms of operator < .

Likewise, the inequality operator is typically implemented in terms of operator == :

When three-way comparison (such as std::memcmp or std::string::compare ) is provided, all six two-way comparison operators may be expressed through that:

[ edit ] Array subscript operator

User-defined classes that provide array-like access that allows both reading and writing typically define two overloads for operator [ ] : const and non-const variants:

If the value type is known to be a scalar type, the const variant should return by value.

Where direct access to the elements of the container is not wanted or not possible or distinguishing between lvalue c [ i ] = v ; and rvalue v = c [ i ] ; usage, operator [ ] may return a proxy. See for example std::bitset::operator[] .

[ edit ] Bitwise arithmetic operators

User-defined classes and enumerations that implement the requirements of BitmaskType are required to overload the bitwise arithmetic operators operator & , operator | , operator ^ , operator~ , operator & = , operator | = , and operator ^ = , and may optionally overload the shift operators operator << operator >> , operator >>= , and operator <<= . The canonical implementations usually follow the pattern for binary arithmetic operators described above.

[ edit ] Boolean negation operator

[ edit ] Rarely overloaded operators

The following operators are rarely overloaded:

• The address-of operator, operator & . If the unary & is applied to an lvalue of incomplete type and the complete type declares an overloaded operator & , it is unspecified whether the operator has the built-in meaning or the operator function is called. Because this operator may be overloaded, generic libraries use std::addressof to obtain addresses of objects of user-defined types. The best known example of a canonical overloaded operator& is the Microsoft class CComPtrBase . An example of this operator's use in EDSL can be found in boost.spirit .
• The boolean logic operators, operator && and operator || . Unlike the built-in versions, the overloads cannot implement short-circuit evaluation. Also unlike the built-in versions, they do not sequence their left operand before the right one. (until C++17) In the standard library, these operators are only overloaded for std::valarray .
• The comma operator, operator, . Unlike the built-in version, the overloads do not sequence their left operand before the right one. (until C++17) Because this operator may be overloaded, generic libraries use expressions such as a, void ( ) ,b instead of a,b to sequence execution of expressions of user-defined types. The boost library uses operator, in boost.assign , boost.spirit , and other libraries. The database access library SOCI also overloads operator, .
• The member access through pointer to member operator - > * . There are no specific downsides to overloading this operator, but it is rarely used in practice. It was suggested that it could be part of a smart pointer interface , and in fact is used in that capacity by actors in boost.phoenix . It is more common in EDSLs such as cpp.react .

[ edit ] Notes

[ edit ] Keywords

[ edit ] example, [ edit ] defect reports.

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[ edit ] See also

• Operator precedence
• Alternative operator syntax
• Argument-dependent lookup

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Assignment Operators In C++

In C++, the assignment operator forms the backbone of many algorithms and computational processes by performing a simple operation like assigning a value to a variable. It is denoted by equal sign ( = ) and provides one of the most basic operations in any programming language that is used to assign some value to the variables in C++ or in other words, it is used to store some kind of information.

The right-hand side value will be assigned to the variable on the left-hand side. The variable and the value should be of the same data type.

The value can be a literal or another variable of the same data type.

Compound Assignment Operators

In C++, the assignment operator can be combined into a single operator with some other operators to perform a combination of two operations in one single statement. These operators are called Compound Assignment Operators. There are 10 compound assignment operators in C++:

• Addition Assignment Operator ( += )
• Subtraction Assignment Operator ( -= )
• Multiplication Assignment Operator ( *= )
• Division Assignment Operator ( /= )
• Modulus Assignment Operator ( %= )
• Bitwise AND Assignment Operator ( &= )
• Bitwise OR Assignment Operator ( |= )
• Bitwise XOR Assignment Operator ( ^= )
• Left Shift Assignment Operator ( <<= )
• Right Shift Assignment Operator ( >>= )

Lets see each of them in detail.

1. Addition Assignment Operator (+=)

In C++, the addition assignment operator (+=) combines the addition operation with the variable assignment allowing you to increment the value of variable by a specified expression in a concise and efficient way.

This above expression is equivalent to the expression:

2. Subtraction Assignment Operator (-=)

The subtraction assignment operator (-=) in C++ enables you to update the value of the variable by subtracting another value from it. This operator is especially useful when you need to perform subtraction and store the result back in the same variable.

3. Multiplication Assignment Operator (*=)

In C++, the multiplication assignment operator (*=) is used to update the value of the variable by multiplying it with another value.

4. Division Assignment Operator (/=)

The division assignment operator divides the variable on the left by the value on the right and assigns the result to the variable on the left.

5. Modulus Assignment Operator (%=)

The modulus assignment operator calculates the remainder when the variable on the left is divided by the value or variable on the right and assigns the result to the variable on the left.

6. Bitwise AND Assignment Operator (&=)

This operator performs a bitwise AND between the variable on the left and the value on the right and assigns the result to the variable on the left.

7. Bitwise OR Assignment Operator (|=)

The bitwise OR assignment operator performs a bitwise OR between the variable on the left and the value or variable on the right and assigns the result to the variable on the left.

8. Bitwise XOR Assignment Operator (^=)

The bitwise XOR assignment operator performs a bitwise XOR between the variable on the left and the value or variable on the right and assigns the result to the variable on the left.

9. Left Shift Assignment Operator (<<=)

The left shift assignment operator shifts the bits of the variable on the left to left by the number of positions specified on the right and assigns the result to the variable on the left.

10. Right Shift Assignment Operator (>>=)

The right shift assignment operator shifts the bits of the variable on the left to the right by a number of positions specified on the right and assigns the result to the variable on the left.

Also, it is important to note that all of the above operators can be overloaded for custom operations with user-defined data types to perform the operations we want.

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How to make compiler use copy instead of move [closed]

I am using msvc compiler with C++ 23

I have a situation like this (class shouldn't be moveable, only copyable):

MyClass m = MyClass{}; //tries to use move

It tries to move the newly constructed class. I realize that this is natural since MyClass{} is an r-value.

Is there anything that I can do to the class to make this possible? Make the compiler understand that I want it to use copy since move is deleted, so that MyClass m = MyClass{}; works?

Error message:

• And if you have an hour, you should watch this presentation: The Nightmare of Initialization in C++ . It'll help you clear up a lot of problems before they happen. –  user4581301 Commented yesterday
• Try this: a) write Myclass m, n; m=n; to test move=; and write a function that returns a local variable of type MyClass, to test move ctor. –  Topological Sort Commented yesterday
• 1 @TopologicalSort m = n; will invoke the copy assignment operator, for the move assignment operator you would need m = std::move(n); instead. Also, a function that returns a named local variable may not invoke the copy constructor or the move constructor at all, if "(Named) Return Value Optimization" (aka copy elison ) is used instead. –  Remy Lebeau Commented yesterday
• Just write MyClass m; or, if you're compulsive, MyClass m{}; . There's no reason to make the construction more complicated. –  Pete Becker Commented yesterday
• Make that m=n1+n2. –  Topological Sort Commented 21 hours ago

Are you SURE you are actually compiling with C++23? Modern MSVC supports C++23, but it defaults to C++14. To actually enable C++23, you need to use the /std flag in your configuration.

In C++17 and later, MyClass m = MyClass{}; is optimized to be identical to MyClass m{}; but that is not the case in earlier versions.

Your code compiles fine in msvc v19 using /std:c++latest .

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• How much missing data is too much (part 2)? statistical power, effective sample size
• Where to donate foreign-language academic books?
• Does a QGIS python script need to be licensed under GNU GPLv2+?
• What are some refutations to the etymological fallacy?
• Do the amplitude and frequency of gravitational waves emitted by binary stars change as the stars get closer together?
• I overstayed 90 days in Switzerland. I have EU residency and never got any stamps in passport. Can I exit/enter at airport without trouble?
• What unique phenomena would be observed in a system around a hypervelocity star?
• Command-line script that strips out all comments in given source files
• Ring Buffer Implementation in C++
• Expected number of numbers that stay at their place after k swaps
• Regression techniques for a “triangular” scatterplot
• Cramer's Rule when the determinant of coefficient matrix is zero?
• Where does the energy in ion propulsion come from?
• If a trigger runs an update will it ALWAYS have the same timestamp for a temporal table?
• Which hash algorithms support binary input of arbitrary bit length?
• Why does flow separation cause an increase in pressure drag?
• Suitable Category in which Orbit-Stabilizer Theorem Arises Naturally as Canonical Decomposition