c compound assignment

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Assignment operators.

Assignment operators modify the value of the object.

[ edit ] Definitions

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

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

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

[ edit ] Assignment operator syntax

The assignment expressions have the form

• ↑ target-expr must have higher precedence than an assignment expression.
• ↑ new-value cannot be a comma expression, because its precedence is lower.

[ edit ] Built-in simple assignment operator

For the built-in simple assignment, the object referred to by target-expr is modified by replacing its value with the result of new-value . target-expr must be a modifiable lvalue.

The result of a built-in simple assignment is an lvalue of the type of target-expr , referring to target-expr . If target-expr is a bit-field , the result is also a bit-field.

[ edit ] Assignment from an expression

If new-value is an expression, it is implicitly converted to the cv-unqualified type of target-expr . When target-expr is a bit-field that cannot represent the value of the expression, the resulting value of the bit-field is implementation-defined.

If target-expr and new-value identify overlapping objects, the behavior is undefined (unless the overlap is exact and the type is the same).

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

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

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:

[ edit ] Built-in compound assignment operator

The behavior of every built-in compound-assignment expression target-expr   op   =   new-value is exactly the same as the behavior of the expression target-expr   =   target-expr   op   new-value , except that target-expr is evaluated only once.

The requirements on target-expr and new-value of built-in simple assignment operators also apply. Furthermore:

• For + = and - = , the type of target-expr must be an arithmetic type or a pointer to a (possibly cv-qualified) completely-defined object type .
• For all other compound assignment operators, the type of target-expr must be an arithmetic type.

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:

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:

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

[ edit ] Example

Possible output:

[ edit ] Defect reports

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

[ edit ] See also

Operator precedence

Operator overloading

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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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Home » Learn C Programming from Scratch » C Assignment Operators

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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Understanding Compound Assignment Operators in C

Understanding compound assignment operators in c - a web page design perspective, introduction, welcome to our web page design guide on compound assignment operators in c.

At [Your Company Name], we believe in creating visually appealing and informative content. In this guide, we'll delve into the world of Compound Assignment Operators in C and explore how they can be utilized to enhance efficiency and readability in your code.

Section 1: What are Compound Assignment Operators?

Compound Assignment Operators in C are a set of operators that combine arithmetic and assignment operations into a single step. They are a convenient way to update the value of a variable based on its current value.

Consider the following code snippet:

In this example, the += operator adds 3 to the current value of x and assigns the result back to x.

Section 2: Commonly Used Compound Assignment Operators

1. += (addition assignment).

This operator adds the right operand to the left operand and assigns the result to the left operand.

2. -= (Subtraction Assignment)

This operator subtracts the right operand from the left operand and assigns the result to the left operand.

3. *= (Multiplication Assignment)

This operator multiplies the left operand by the right operand and assigns the result to the left operand.

4. /= (Division Assignment)

This operator divides the left operand by the right operand and assigns the result to the left operand.

5. %= (Modulus Assignment)

This operator performs a modulus operation on the left operand with the right operand and assigns the result to the left operand.

Section 3: Advantages of Using Compound Assignment Operators

1. conciseness and readability.

By combining the operation and assignment, compound operators make code more concise and easier to read.

2. Improved Efficiency

They can lead to more efficient code execution, especially in situations where the same variable is used in multiple operations.

3. Reduced Risk of Errors

Using compound assignment operators reduces the chance of making mistakes that can occur when writing separate arithmetic and assignment statements.

Section 4: Best Practices for Utilizing Compound Assignment Operators

1. use appropriately.

While compound assignment operators are powerful tools, it's essential to use them judiciously. Overuse or misuse can lead to code that is difficult to understand.

2. Ensure Compatibility

Make sure that the operands on both sides of the operator are compatible. For example, adding an integer to a float using += might lead to unexpected results.

3. Comment for Clarity

In complex operations, consider adding comments to explain the logic behind the use of compound assignment operators.

Congratulations! You've now gained a solid understanding of Compound Assignment Operators in C from a web page design perspective. By incorporating these operators into your code, you can create more efficient and readable programs. If you have any further questions or need assistance with web page design, feel free to reach out to us at [Your Contact Information].

Happy coding!

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Compound-Assignment Operators

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Compound-assignment operators provide a shorter syntax for assigning the result of an arithmetic or bitwise operator. They perform the operation on the two operands before assigning the result to the first operand.

Compound-Assignment Operators in Java

Java supports 11 compound-assignment operators:

Example Usage

To assign the result of an addition operation to a variable using the standard syntax:

But use a compound-assignment operator to effect the same outcome with the simpler syntax:

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+= operator

• Add operation.
• Assignment of the result of add operation.
• Statement i+=2 is equal to i=i+2 , hence 2 will be added to the value of i, which gives us 4.
• Finally, the result of addition, 4 is assigned back to i, updating its original value from 2 to 4.

Example with += operator

-= operator.

• Subtraction operation.
• Assignment of the result of subtract operation.
• Statement i-=2 is equal to i=i-2 , hence 2 will be subtracted from the value of i, which gives us 0.
• Finally, the result of subtraction i.e. 0 is assigned back to i, updating its value to 0.

Example with -= operator

*= operator.

• Multiplication operation.
• Assignment of the result of multiplication operation.
• Statement i*=2 is equal to i=i*2 , hence 2 will be multiplied with the value of i, which gives us 4.
• Finally, the result of multiplication, 4 is assigned back to i, updating its value to 4.

Example with *= operator

/= operator.

• Division operation.
• Assignment of the result of division operation.
• Statement i/=2 is equal to i=i/2 , hence 4 will be divided by the value of i, which gives us 2.
• Finally, the result of division i.e. 2 is assigned back to i, updating its value from 4 to 2.

Example with /= operator

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Using Compound Assignment Operators in C: A Beginner's Guide

An assignment operator is used for assigning a value to a variable. The most common assignment operator is = (equal). The left side operand of the assignment operator is a variable and 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 variable on the left side otherwise the compiler will raise an error.

The code is a C program that demonstrates the use of compound assignment operators in C. Here is an explanation of each line of the code:

• int a=10,b=5; declares two variables a and b of type int and assigns them the values 10 and 5 respectively.
• a+=b; is the compound assignment operator +=, it performs a+b and assigns the value to a. It is equivalent to a=a+b.
• printf("A : %d",a); prints the value of a which is 15, this is the result after using += operator.
• a-=10; is the compound assignment operator -=, it performs a-10 and assigns the value to a. It is equivalent to a=a-10.
• printf("\nA : %d",a); prints the value of a which is 5, this is the result after using -= operator.
• return 0; The return 0; statement is used to indicate that the main function has completed successfully. The value 0 is returned as the exit status of the program, which indicates a successful execution.

When you run this code, it will perform the compound assignment operation on variables and print the results in the console.

Source Code

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Assignment Operators in C

Assignment operators are used for assigning value to a variable. The left side operand of the assignment operator is a variable and 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 variable on the left side otherwise the compiler will raise an error.

Different types of assignment operators are shown below:

1. “=”: This is the simplest assignment operator. This operator is used to assign the value on the right to the variable on the left. Example:

2. “+=” : This operator is combination of ‘+’ and ‘=’ operators. This operator first adds the current value of the variable on left to the value on the right and then assigns the result to the variable on the left. Example:

If initially value stored in a is 5. Then (a += 6) = 11.

3. “-=” This operator is combination of ‘-‘ and ‘=’ operators. This operator first subtracts the value on the right from the current value of the variable on left and then assigns the result to the variable on the left. Example:

If initially value stored in a is 8. Then (a -= 6) = 2.

4. “*=” This operator is combination of ‘*’ and ‘=’ operators. This operator first multiplies the current value of the variable on left to the value on the right and then assigns the result to the variable on the left. Example:

If initially value stored in a is 5. Then (a *= 6) = 30.

5. “/=” This operator is combination of ‘/’ and ‘=’ operators. This operator first divides the current value of the variable on left by the value on the right and then assigns the result to the variable on the left. Example:

If initially value stored in a is 6. Then (a /= 2) = 3.

Below example illustrates the various Assignment Operators:

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Compound Assignment Operators in C++

The compound assignment operators are specified in the form e1 op= e2, where e1 is a modifiable l-value not of const type and e2 is one of the following −

• An arithmetic type
• A pointer, if op is + or –

The e1 op= e2 form behaves as e1 = e1 op e2, but e1 is evaluated only once.

The following are the compound assignment operators in C++ −

Let's have a look at an example using some of these operators −

This will give the output −

Note that 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. If the left operand is of an integral type, the right operand must not be of a pointer type.

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Is chained assignment in C/C++ undefined behavior?

Ignoring the types of variables, is expression like a=b=c has defined behavior in both C and C++?

If so, can any one give me official evidence, like quotes from the standard, please?

P.S. I searched the chained assignment but everything I got is associativity, but I didn't find any text about that in the C99 standard. Maybe I did it wrong? hoping anyone can help me.

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• Are we assuming that a , b and c are not the same variable? If they are the same it is more intereting . –  Shafik Yaghmour Commented Mar 24, 2014 at 12:16
• 1 I don't think it warrants any explicit mention in the standards, because an assignment is just an expression which returns the result of the assignment, so a=b=c is equivalent to a=(b=c) and this is no different, in essence, than a=b+c . –  Paul R Commented Mar 24, 2014 at 12:16
• 1 a=b=c hasn't anything with the associativity to do. It will be interpreted as a=(b=c), also b=c;a=(b==0)?1:0 . Sorry, I didn't see qny reason to dig in the standard, it is at the beginning of every c/c++ book. –  peterh Commented Mar 24, 2014 at 12:18

4 Answers 4

From the C++ Standard

5.17 Assignment and compound assignment operators [expr.ass] 1 The assignment operator (=) and the compound assignment operators all group right-to-left. All require a modifiable lvalue as their left operand and return an lvalue referring to the left operand . The result in all cases is a bit-field if the left operand is a bit-field. In all cases, the assignment is sequenced after the value computation of the right and left operands, and before the value computation of the assignment expression.

And an example from there

From the C Standard

6.5.16 Assignment operators Semantics 3 An assignment operator stores a value in the object designated by the left operand. An assignment expression has the value of the left operand after the assignment,111) but is not an lvalue . The type of an assignment expression is the type the left operand would have after lvalue conversion. The side effect of updating the stored value of the left operand is sequenced after the value computations of the left and right operands. The evaluations of the operands are unsequenced.

As you see there is a difference. In C++ the assignment operator returns an lvalue referring to the left operand while in C it returns the value of the left operand after the assignment,111) but is not an lvalue .

It means that in C++ the following code is valid

while in C the compiler shall issue an error.

• Are all operations in C/C++ grouped from right to left? –  martixingwei Commented Mar 24, 2014 at 20:16
• @martixingwei No they are not. You should read the description of each category of operators. For example expressions with unary operators group right to left while postfix expressions group left to right. –  Vlad from Moscow Commented Mar 24, 2014 at 20:19

According to §6.5.16 (3) of C99:

An assignment expression has the value of the left operand after the assignment, [...]

Together with right-associativity of evaluation, and assuming non-volatile a , b , and c , it means that a = b = c is equivalent to a = (b = c) , and again equivalent to b = c; a = b .

• 2 I have not found this quite true in practice. Or at least gcc C99 implementation is not up to scratch. a = b = c; looks to be equivalent to b = c; a = c;. Try making b a volatile variable: 'a = b = c;' does not generate read of b. While 'b = c; a = b;' would generate reread of b after write. –  user377178 Commented Oct 16, 2017 at 7:53
• @user377178 Good catch. The answer was written informally to explain the semantics, and assumed local and non-volatile variables where all reads and writes can be reordered or even entirely omitted. I've now made the assumption explicit. Another option would be to describe b = c as _tmp = c; b = _tmp and therefore a = b = c as equivalent to _tmp = c; b = _tmp; a = _tmp , but that seems like sacrificing beginner-level clarity for the sake of expert-level accuracy. –  user4815162342 Commented Oct 16, 2017 at 8:31

It C, and C++, assignment is right associative and also an expression, so

Is treated as:

Where the expression b=c evaluates to whatever is in b after the assignment. Note that I say "whatever` as it's possible (but not advisable) in C++ to provide an assigment function that does something other that assignment!

• 2 "Whatever" also matters for C. Unless the value c is representable in the type of b , b=c has value different from c . –  R.. GitHub STOP HELPING ICE Commented Mar 24, 2014 at 13:28

It is all about associativity. You can rewrite a=b=c as a=(b=c) . And the result of an assignment ( b=c ) is the value of the last assigned variable ( b ).

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