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Assignment operators
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expression assignment-operator expression
assignment-operator : one of = *= /= %= += -= <<= >>= &= ^= |=
Assignment operators store a value in the object specified by the left operand. There are two kinds of assignment operations:
simple assignment , in which the value of the second operand is stored in the object specified by the first operand.
compound assignment , in which an arithmetic, shift, or bitwise operation is performed before storing the result.
All assignment operators in the following table except the = operator are compound assignment operators.
Assignment operators table
Operator keywords.
Three of the compound assignment operators have keyword equivalents. They are:
C++ specifies these operator keywords as alternative spellings for the compound assignment operators. In C, the alternative spellings are provided as macros in the <iso646.h> header. In C++, the alternative spellings are keywords; use of <iso646.h> or the C++ equivalent <ciso646> is deprecated. In Microsoft C++, the /permissive- or /Za compiler option is required to enable the alternative spelling.
Simple assignment
The simple assignment operator ( = ) causes the value of the second operand to be stored in the object specified by the first operand. If both objects are of arithmetic types, the right operand is converted to the type of the left, before storing the value.
Objects of const and volatile types can be assigned to l-values of types that are only volatile , or that aren't const or volatile .
Assignment to objects of class type ( struct , union , and class types) is performed by a function named operator= . The default behavior of this operator function is to perform a member-wise copy assignment of the object's non-static data members and direct base classes; however, this behavior can be modified using overloaded operators. For more information, see Operator overloading . Class types can also have copy assignment and move assignment operators. For more information, see Copy constructors and copy assignment operators and Move constructors and move assignment operators .
An object of any unambiguously derived class from a given base class can be assigned to an object of the base class. The reverse isn't true because there's an implicit conversion from derived class to base class, but not from base class to derived class. For example:
Assignments to reference types behave as if the assignment were being made to the object to which the reference points.
For class-type objects, assignment is different from initialization. To illustrate how different assignment and initialization can be, consider the code
The preceding code shows an initializer; it calls the constructor for UserType2 that takes an argument of type UserType1 . Given the code
the assignment statement
can have one of the following effects:
Call the function operator= for UserType2 , provided operator= is provided with a UserType1 argument.
Call the explicit conversion function UserType1::operator UserType2 , if such a function exists.
Call a constructor UserType2::UserType2 , provided such a constructor exists, that takes a UserType1 argument and copies the result.
Compound assignment
The compound assignment operators are shown in the Assignment operators table . These operators have the form e1 op = e2 , where e1 is a non- const modifiable l-value and e2 is:
an arithmetic type
a pointer, if op is + or -
a type for which there exists a matching operator *op*= overload for the type of e1
The built-in e1 op = e2 form behaves as e1 = e1 op e2 , but e1 is evaluated only once.
Compound assignment to an enumerated type generates an error message. If the left operand is of a pointer type, the right operand must be of a pointer type, or it must be a constant expression that evaluates to 0. When the left operand is of an integral type, the right operand must not be of a pointer type.
Result of built-in assignment operators
The built-in assignment operators return the value of the object specified by the left operand after the assignment (and the arithmetic/logical operation in the case of compound assignment operators). The resultant type is the type of the left operand. The result of an assignment expression is always an l-value. These operators have right-to-left associativity. The left operand must be a modifiable l-value.
In ANSI C, the result of an assignment expression isn't an l-value. That means the legal C++ expression (a += b) += c isn't allowed in C.
Expressions with binary operators C++ built-in operators, precedence, and associativity C assignment operators
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Java Assignment Operators with Examples
Operators constitute the basic building block of any programming language. Java too provides many types of operators which can be used according to the need to perform various calculations and functions, be it logical, arithmetic, relational, etc. They are classified based on the functionality they provide.
Types of Operators:
- Arithmetic Operators
- Unary Operators
- Assignment Operator
- Relational Operators
- Logical Operators
- Ternary Operator
- Bitwise Operators
- Shift Operators
This article explains all that one needs to know regarding Assignment Operators.
Assignment Operators
These operators are used to assign values to a variable. The left side operand of the assignment operator is a variable, and the right side operand of the assignment operator is a value. The value on the right side must be of the same data type of the operand on the left side. Otherwise, the compiler will raise an error. This means that the assignment operators have right to left associativity, i.e., the value given on the right-hand side of the operator is assigned to the variable on the left. Therefore, the right-hand side value must be declared before using it or should be a constant. The general format of the assignment operator is,
Types of Assignment Operators in Java
The Assignment Operator is generally of two types. They are:
1. Simple Assignment Operator: The Simple Assignment Operator is used with the “=” sign where the left side consists of the operand and the right side consists of a value. The value of the right side must be of the same data type that has been defined on the left side.
2. Compound Assignment Operator: The Compound Operator is used where +,-,*, and / is used along with the = operator.
Let’s look at each of the assignment operators and how they operate:
1. (=) operator:
This is the most straightforward assignment operator, which is used to assign the value on the right to the variable on the left. This is the basic definition of an assignment operator and how it functions.
Syntax:
Example:
2. (+=) operator:
This operator is a compound of ‘+’ and ‘=’ operators. It operates by adding the current value of the variable on the left to the value on the right and then assigning the result to the operand on the left.
Note: The compound assignment operator in Java performs implicit type casting. Let’s consider a scenario where x is an int variable with a value of 5. int x = 5; If you want to add the double value 4.5 to the integer variable x and print its value, there are two methods to achieve this: Method 1: x = x + 4.5 Method 2: x += 4.5 As per the previous example, you might think both of them are equal. But in reality, Method 1 will throw a runtime error stating the “i ncompatible types: possible lossy conversion from double to int “, Method 2 will run without any error and prints 9 as output.
Reason for the Above Calculation
Method 1 will result in a runtime error stating “incompatible types: possible lossy conversion from double to int.” The reason is that the addition of an int and a double results in a double value. Assigning this double value back to the int variable x requires an explicit type casting because it may result in a loss of precision. Without the explicit cast, the compiler throws an error. Method 2 will run without any error and print the value 9 as output. The compound assignment operator += performs an implicit type conversion, also known as an automatic narrowing primitive conversion from double to int . It is equivalent to x = (int) (x + 4.5) , where the result of the addition is explicitly cast to an int . The fractional part of the double value is truncated, and the resulting int value is assigned back to x . It is advisable to use Method 2 ( x += 4.5 ) to avoid runtime errors and to obtain the desired output.
Same automatic narrowing primitive conversion is applicable for other compound assignment operators as well, including -= , *= , /= , and %= .
3. (-=) operator:
This operator is a compound of ‘-‘ and ‘=’ operators. It operates by subtracting the variable’s value on the right from the current value of the variable on the left and then assigning the result to the operand on the left.
4. (*=) operator:
This operator is a compound of ‘*’ and ‘=’ operators. It operates by multiplying the current value of the variable on the left to the value on the right and then assigning the result to the operand on the left.
5. (/=) operator:
This operator is a compound of ‘/’ and ‘=’ operators. It operates by dividing the current value of the variable on the left by the value on the right and then assigning the quotient to the operand on the left.
6. (%=) operator:
This operator is a compound of ‘%’ and ‘=’ operators. It operates by dividing the current value of the variable on the left by the value on the right and then assigning the remainder to the operand on the left.
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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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