compound let assignment

Java Compound Operators

Last updated: March 17, 2024

• Java Operators

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1. Overview

In this tutorial, we’ll have a look at Java compound operators, their types and how Java evaluates them.

We’ll also explain how implicit casting works.

2. Compound Assignment Operators

An assignment operator is a binary operator that assigns the result of the right-hand side to the variable on the left-hand side. The simplest is the “=” assignment operator:

This statement declares a new variable x , assigns x the value of 5 and returns 5 .

Compound Assignment Operators are a shorter way to apply an arithmetic or bitwise operation and to assign the value of the operation to the variable on the left-hand side.

For example, the following two multiplication statements are equivalent, meaning  a and b will have the same value:

It’s important to note that the variable on the left-hand of a compound assignment operator must be already declared. In other words,  compound operators can’t be used to declare a new variable.

Like the “=” assignment operator, compound operators return the assigned result of the expression:

Both x and y will hold the value 3 .

The assignment (x+=2) does two things: first, it adds 2 to the value of the variable x , which becomes  3;  second, it returns the value of the assignment, which is also 3 .

3. Types of Compound Assignment Operators

Java supports 11 compound assignment operators. We can group these into arithmetic and bitwise operators.

Let’s go through the arithmetic operators and the operations they perform:

• Incrementation: +=
• Decrementation: -=
• Multiplication: *=
• Division: /=
• Modulus: %=

Then, we also have the bitwise operators:

• AND, binary: &=
• Exclusive OR, binary: ^=
• Inclusive OR, binary: |=
• Left Shift, binary: <<=
• Right Shift, binary: >>=
• Shift right zero fill: >>>=

Let’s have a look at a few examples of these operations:

As we can see here, the syntax to use these operators is consistent.

4. Evaluation of Compound Assignment Operations

There are two ways Java evaluates the compound operations.

First, when the left-hand operand is not an array, then Java will, in order:

• Verify the operand is a declared variable
• Save the value of the left-hand operand
• Evaluate the right-hand operand
• Perform the binary operation as indicated by the compound operator
• Convert the result of the binary operation to the type of the left-hand variable (implicit casting)
• Assign the converted result to the left-hand variable

Next, when the left-hand operand is an array, the steps to follow are a bit different:

• Verify the array expression on the left-hand side and throw a NullPointerException  or  ArrayIndexOutOfBoundsException if it’s incorrect
• Save the array element in the index
• Check if the array component selected is a primitive type or reference type and then continue with the same steps as the first list, as if the left-hand operand is a variable.

If any step of the evaluation fails, Java doesn’t continue to perform the following steps.

Let’s give some examples related to the evaluation of these operations to an array element:

As we’d expect, this will throw a  NullPointerException .

However, if we assign an initial value to the array:

We would get rid of the NullPointerException, but we’d still get an  ArrayIndexOutOfBoundsException , as the index used is not correct.

If we fix that, the operation will be completed successfully:

Finally, the x variable will be 6 at the end of the assignment.

5. Implicit Casting

One of the reasons compound operators are useful is that not only they provide a shorter way for operations, but also implicitly cast variables.

Formally, a compound assignment expression of the form:

is equivalent to:

E1 – (T)(E1 op E2)

where T is the type of E1 .

Let’s consider the following example:

Let’s review why the last line won’t compile.

Java automatically promotes smaller data types to larger data ones, when they are together in an operation, but will throw an error when trying to convert from larger to smaller types .

So, first,  i will be promoted to long and then the multiplication will give the result 10L. The long result would be assigned to i , which is an int , and this will throw an error.

This could be fixed with an explicit cast:

Java compound assignment operators are perfect in this case because they do an implicit casting:

This statement works just fine, casting the multiplication result to int and assigning the value to the left-hand side variable, i .

6. Conclusion

In this article, we looked at compound operators in Java, giving some examples and different types of them. We explained how Java evaluates these operations.

Finally, we also reviewed implicit casting, one of the reasons these shorthand operators are useful.

As always, all of the code snippets mentioned in this article can be found in our GitHub repository .

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Assignment Operators in Programming

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• Operator Associativity in Programming
• C++ Assignment Operator Overloading
• What are Operators in Programming?
• Assignment Operators In C++
• Bitwise AND operator in Programming
• Increment and Decrement Operators in Programming
• Types of Operators in Programming
• Logical AND operator in Programming
• Modulus Operator in Programming
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Assignment operators in programming are symbols used to assign values to variables. They offer shorthand notations for performing arithmetic operations and updating variable values in a single step. These operators are fundamental in most programming languages and help streamline code while improving readability.

Table of Content

What are Assignment Operators?

• Types of Assignment Operators
• Assignment Operators in C++
• Assignment Operators in Java
• Assignment Operators in C#
• Assignment Operators in Javascript
• Application of Assignment Operators

Assignment operators are used in programming to  assign values  to variables. We use an assignment operator to store and update data within a program. They enable programmers to store data in variables and manipulate that data. The most common assignment operator is the equals sign ( = ), which assigns the value on the right side of the operator to the variable on the left side.

Types of Assignment Operators:

• Simple Assignment Operator ( = )
• Addition Assignment Operator ( += )
• Subtraction Assignment Operator ( -= )
• Multiplication Assignment Operator ( *= )
• Division Assignment Operator ( /= )
• Modulus Assignment Operator ( %= )

Below is a table summarizing common assignment operators along with their symbols, description, and examples:

Assignment Operators in C:

Here are the implementation of Assignment Operator in C language:

Assignment Operators in C++:

Here are the implementation of Assignment Operator in C++ language:

Assignment Operators in Java:

Here are the implementation of Assignment Operator in java language:

Assignment Operators in Python:

Here are the implementation of Assignment Operator in python language:

Assignment Operators in C#:

Here are the implementation of Assignment Operator in C# language:

Assignment Operators in Javascript:

Here are the implementation of Assignment Operator in javascript language:

Application of Assignment Operators:

• Variable Initialization : Setting initial values to variables during declaration.
• Mathematical Operations : Combining arithmetic operations with assignment to update variable values.
• Loop Control : Updating loop variables to control loop iterations.
• Conditional Statements : Assigning different values based on conditions in conditional statements.
• Function Return Values : Storing the return values of functions in variables.
• Data Manipulation : Assigning values received from user input or retrieved from databases to variables.

Conclusion:

In conclusion, assignment operators in programming are essential tools for assigning values to variables and performing operations in a concise and efficient manner. They allow programmers to manipulate data and control the flow of their programs effectively. Understanding and using assignment operators correctly is fundamental to writing clear, efficient, and maintainable code in various programming languages.

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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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Now that we've talked about operators. Let's talk about something called the compound assignment operator and I'm going make one little change here in case you're wondering if you ever want to have your console take up the entire window you come up to the top right-hand side here you can undock it into a separate window and you can see that it takes up the entire window.

So just a little bit more room now.

Additionally, I have one other thing I'm going to show you in the show notes. I'm going to give you access to this entire set of assignment operators but we'll go through a few examples here. I'm going to use the entire window just to make it a little bit easier to see.

Let's talk about what assignment is. Now we've been using assignment ever since we started writing javascript code. You're probably pretty used to it. Assignment is saying something like var name and then setting up a name

And that is assignment the equals represents assignment.

Now javascript gives us the ability to have the regular assignment but also to have that assignment perform tasks. So for example say that you want to add items up so say that we want to add up a total set of grades to see the total number of scores. I can say var sum and assign it equal to zero.

And now let's create some grades.

I'm going to say var gradeOne = 100.

and then var gradeTwo = 80.

Now with both of these items in place say that we wanted to add these if you wanted to just add both of them together you definitely could do something like sum = (gradeOne + gradeTwo); and that would work.

However, one thing I want to show you is, there are many times where you don't have gradeOne or gradeTwo in a variable. You may have those stored in a database and then you're going to loop through that full set of records. And so you need to be able to add them on the fly. And so that's what a compound assignment operator can do.

Let's use one of the more basic ones which is to have the addition assignment.

Now you can see that sum is equal to 100.

Then if I do

If we had 100 grades we could simply add them just like that.

Essentially what this is equal to is it's a shorthand for saying something like

sum = sum + whatever the next one is say, that we had a gradeThree, it would be the same as doing that. So it's performing assignment, but it also is performing an operation. That's the reason why it's called a compound assignment operator.

Now in addition to having the ability to sum items up, you could also do the same thing with the other operators. In fact literally, every one of the operators that we just went through you can use those in order to do this compound assignment. Say that you wanted to do multiplication you could do sum astrix equals and then gradeTwo and now you can see it equals fourteen thousand four hundred.

This is that was the exact same as doing sum = whatever the value of sum was times gradeTwo. That gives you the exact same type of process so that is how you can use the compound assignment operators. And if you reference the guide that is included in the show notes. You can see that we have them for each one of these from regular equals all the way through using exponents.

Then for right now don't worry about the bottom items. These are getting into much more advanced kinds of fields like bitwise operators and right and left shift assignments. So everything you need to focus on is actually right at the top for how we're going to be doing this. This is something that you will see in a javascript code. I wanted to include it, so when you see it you're not curious about exactly what's happening.

It's a great shorthand syntax for whenever you want to do assignment but also perform an operation at the same time.

• Documentation for Compound Assignment Operators
• Source code

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1.4 Compound Assignment Operators

7 min read • december 27, 2022

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Compound Assignment Operators

Compound operators.

Sometimes, you will encounter situations where you need to perform the following operation:

This is a bit clunky with the repetition of integerOne in line two. We can condense this with this statement:

The "* = 2" is an example of a compound assignment operator , which multiplies the current value of integerOne by 2 and sets that as the new value of integerOne. Other arithmetic operators also have compound assignment operators as well, with addition, subtraction, division, and modulo having +=, -=, /=, and %=, respectively.

Incrementing and Decrementing

There are special operators for the two following operations in the following snippet well:

These can be replaced with a pre-increment /pre-decrement (++i or - -i) or post-increment /post-decrement (i++ or i- -) operator . You only need to know the post-variant in this course, but it is useful to know the difference between the two. Here is an example demonstrating the difference between them:

By itself, there is no difference between the pre-increment and post-increment operators, but it's evident when you use it in a method such as the println method. For this statement, I will write a debugging output , which happens when we trace the code, which means to follow it line-by-line.

Code Tracing Practice

Now that you’ve learned about code tracing , let’s do some practice! You can use trace tables like the ones shown below to keep track of the values of your variables as they change.

Here are some practice problems that you can use to practice code tracing . Feel free to use whichever method you’re the most comfortable with!

Trace through the following code:

Note: Your answers could look different depending on how you’re tracking your code tracing .

a *= 3: This line multiplies a by 3 and assigns the result back to a. The value of a is now 18.

b -= 2: This line subtracts 2 from b and assigns the result back to b. The value of b is now 2.

c = a % b: This line calculates the remainder of a divided by b and assigns the result to c. The value of c is now 0.

a += c: This line adds c to a and assigns the result back to a. The value of a is now 18.

b = a - b: This line subtracts b from a and assigns the result back to b. The value of b is now 16.

c *= b: This line multiplies c by b and assigns the result back to c. The value of c is now 0.

The final values of the variables are:

double x = 15.0;

double y = 4.0;

double z = 0;

x /= y: This line divides x by y and assigns the result back to x. The value of x is now 3.75.

y *= x: This line multiplies y by x and assigns the result back to y. The value of y is now 15.0.

z = y % x: This line calculates the remainder of y divided by x and assigns the result to z. The value of z is now 3.75.

x += z: This line adds z to x and assigns the result back to x. The value of x is now 7.5.

y = x / z: This line divides x by z and assigns the result back to y. The value of y is now 2.0.

z *= y: This line multiplies z by y and assigns the result back to z. The value of z is now 7.5.

int a = 100;

int b = 50;

int c = 25;

a -= b: This line subtracts b from a and assigns the result back to a. The value of a is now 50.

b *= 2: This line multiplies b by 2 and assigns the result back to b. The value of b is now 100.

c %= 4: This line calculates the remainder of c divided by 4 and assigns the result back to c. The value of c is now 1.

a = b + c: This line adds b and c and assigns the result to a. The value of a is now 101.

b = c - a: This line subtracts a from c and assigns the result to b. The value of b is now -100.

c = a * b: This line multiplies a and b and assigns the result to c. The value of c is now -10201.

a *= 2: This line multiplies a by 2 and assigns the result back to a. The value of a is now 10.

b -= 1: This line subtracts 1 from b and assigns the result back to b. The value of b is now 2.

a += c: This line adds c to a and assigns the result back to a. The value of a is now 10.

b = a - b: This line subtracts b from a and assigns the result back to b. The value of b is now 8.

int y = 10;

int z = 15;

x *= 2: This line multiplies x by 2 and assigns the result back to x. The value of x is now 10.

y /= 3: This line divides y by 3 and assigns the result back to y. The value of y is now 3.3333... (rounded down to 3).

z -= x: This line subtracts x from z and assigns the result back to z. The value of z is now 5.

x = y + z: This line adds y and z and assigns the result to x. The value of x is now 8.

y = z - x: This line subtracts x from z and assigns the result to y. The value of y is now -3.

z = x * y: This line multiplies x and y and assigns the result to z. The value of z is now -24.

double x = 10;

double y = 3;

x /= y: This line divides x by y and assigns the result back to x. The value of x is now 3.3333... (rounded down to 3.33).

y *= x: This line multiplies y by x and assigns the result back to y. The value of y is now 10.

z = y - x: This line subtracts x from y and assigns the result to z. The value of z is now 6.67.

x += z: This line adds z to x and assigns the result back to x. The value of x is now 10.0.

y = x / z: This line divides x by z and assigns the result back to y. The value of y is now 1.5.

z *= y: This line multiplies z by y and assigns the result back to z. The value of z is now 10.0.

Want some additional practice? CSAwesome created this really cool Operators Maze game that you can do with a friend for a little extra practice! 

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1.5. Compound Assignment Operators ¶

Compound assignment operators are shortcuts that do a math operation and assignment in one step. For example, x += 1 adds 1 to the current value of x and assigns the result back to x . It is the same as x = x + 1 . This pattern is possible with any operator put in front of the = sign, as seen below. If you need a mnemonic to remember whether the compound operators are written like += or =+ , just remember that the operation ( + ) is done first to produce the new value which is then assigned ( = ) back to the variable. So it’s operator then equal sign: += .

Since changing the value of a variable by one is especially common, there are two extra concise operators ++ and -- , also called the plus-plus or increment operator and minus-minus or decrement operator that set a variable to one greater or less than its current value.

Thus x++ is even more concise way to write x = x + 1 than the compound operator x += 1 . You’ll see this shortcut used a lot in loops when we get to them in Unit 4. Similarly, y-- is a more concise way to write y = y - 1 . These shortcuts only exist for + and - as they don’t really make sense for other operators.

If you’ve heard of the programming language C++, the name is an inside joke that C, an earlier language which C++ is based on, had been incremented or improved to create C++.

Here’s a table of all the compound arithmetic operators and the extra concise incremend and decrement operators and how they relate to fully written out assignment expressions. You can run the code below the table to see these shortcut operators in action!

Run the code below to see what the ++ and shorcut operators do. Click on the Show Code Lens button to trace through the code and the variable values change in the visualizer. Try creating more compound assignment statements with shortcut operators and work with a partner to guess what they would print out before running the code.

If you look at real-world Java code, you may occassionally see the ++ and -- operators used before the name of the variable, like ++x rather than x++ . That is legal but not something that you will see on the AP exam.

Putting the operator before or after the variable only changes the value of the expression itself. If x is 10 and we write, System.out.println(x++) it will print 10 but aftewards x will be 11. On the other hand if we write, System.out.println(++x) , it will print 11 and afterwards the value will be 11.

In other words, with the operator after the variable name, (called the postfix operator) the value of the variable is changed after evaluating the variable to get its value. And with the operator before the variable (the prefix operator) the value of the variable in incremented before the variable is evaluated to get the value of the expression.

But the value of x after the expression is evaluated is the same in either case: one greater than what it was before. The -- operator works similarly.

The AP exam will never use the prefix form of these operators nor will it use the postfix operators in a context where the value of the expression matters.

1-5-2: What are the values of x, y, and z after the following code executes?

• x = -1, y = 1, z = 4
• This code subtracts one from x, adds one to y, and then sets z to to the value in z plus the current value of y.
• x = -1, y = 2, z = 3
• x = -1, y = 2, z = 2
• x = 0, y = 1, z = 2
• x = -1, y = 2, z = 4

1-5-3: What are the values of x, y, and z after the following code executes?

• x = 6, y = 2.5, z = 2
• This code sets x to z * 2 (4), y to y divided by 2 (5 / 2 = 2) and z = to z + 1 (2 + 1 = 3).
• x = 4, y = 2.5, z = 2
• x = 6, y = 2, z = 3
• x = 4, y = 2.5, z = 3
• x = 4, y = 2, z = 3

1.5.1. Code Tracing Challenge and Operators Maze ¶

Use paper and pencil or the question response area below to trace through the following program to determine the values of the variables at the end.

Code Tracing is a technique used to simulate a dry run through the code or pseudocode line by line by hand as if you are the computer executing the code. Tracing can be used for debugging or proving that your program runs correctly or for figuring out what the code actually does.

Trace tables can be used to track the values of variables as they change throughout a program. To trace through code, write down a variable in each column or row in a table and keep track of its value throughout the program. Some trace tables also keep track of the output and the line number you are currently tracing.

Trace through the following code:

1-5-4: Write your trace table for x, y, and z here showing their results after each line of code.

After doing this challenge, play the Operators Maze game . See if you and your partner can get the highest score!

1.5.2. Summary ¶

Compound assignment operators ( += , -= , *= , /= , %= ) can be used in place of the assignment operator.

The increment operator ( ++ ) and decrement operator ( -- ) are used to add 1 or subtract 1 from the stored value of a variable. The new value is assigned to the variable.

The use of increment and decrement operators in prefix form (e.g., ++x ) and inside other expressions (i.e., arr[x++] ) is outside the scope of this course and the AP Exam.

cppreference.com

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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Expressions and operators

This chapter describes JavaScript's expressions and operators, including assignment, comparison, arithmetic, bitwise, logical, string, ternary and more.

At a high level, an expression is a valid unit of code that resolves to a value. There are two types of expressions: those that have side effects (such as assigning values) and those that purely evaluate .

The expression x = 7 is an example of the first type. This expression uses the = operator to assign the value seven to the variable x . The expression itself evaluates to 7 .

The expression 3 + 4 is an example of the second type. This expression uses the + operator to add 3 and 4 together and produces a value, 7 . However, if it's not eventually part of a bigger construct (for example, a variable declaration like const z = 3 + 4 ), its result will be immediately discarded — this is usually a programmer mistake because the evaluation doesn't produce any effects.

As the examples above also illustrate, all complex expressions are joined by operators , such as = and + . In this section, we will introduce the following operators:

Assignment operators

Comparison operators, arithmetic operators, bitwise operators, logical operators, bigint operators, string operators, conditional (ternary) operator, comma operator, unary operators, relational operators.

These operators join operands either formed by higher-precedence operators or one of the basic expressions . A complete and detailed list of operators and expressions is also available in the reference .

The precedence of operators determines the order they are applied when evaluating an expression. For example:

Despite * and + coming in different orders, both expressions would result in 7 because * has precedence over + , so the * -joined expression will always be evaluated first. You can override operator precedence by using parentheses (which creates a grouped expression — the basic expression). To see a complete table of operator precedence as well as various caveats, see the Operator Precedence Reference page.

JavaScript has both binary and unary operators, and one special ternary operator, the conditional operator. A binary operator requires two operands, one before the operator and one after the operator:

For example, 3 + 4 or x * y . This form is called an infix binary operator, because the operator is placed between two operands. All binary operators in JavaScript are infix.

A unary operator requires a single operand, either before or after the operator:

For example, x++ or ++x . The operator operand form is called a prefix unary operator, and the operand operator form is called a postfix unary operator. ++ and -- are the only postfix operators in JavaScript — all other operators, like ! , typeof , etc. are prefix.

An assignment operator assigns a value to its left operand based on the value of its right operand. The simple assignment operator is equal ( = ), which assigns the value of its right operand to its left operand. That is, x = f() is an assignment expression that assigns the value of f() to x .

There are also compound assignment operators that are shorthand for the operations listed in the following table:

Assigning to properties

If an expression evaluates to an object , then the left-hand side of an assignment expression may make assignments to properties of that expression. For example:

For more information about objects, read Working with Objects .

If an expression does not evaluate to an object, then assignments to properties of that expression do not assign:

In strict mode , the code above throws, because one cannot assign properties to primitives.

It is an error to assign values to unmodifiable properties or to properties of an expression without properties ( null or undefined ).

Destructuring

For more complex assignments, the destructuring assignment syntax is a JavaScript expression that makes it possible to extract data from arrays or objects using a syntax that mirrors the construction of array and object literals.

Without destructuring, it takes multiple statements to extract values from arrays and objects:

With destructuring, you can extract multiple values into distinct variables using a single statement:

Evaluation and nesting

In general, assignments are used within a variable declaration (i.e., with const , let , or var ) or as standalone statements.

However, like other expressions, assignment expressions like x = f() evaluate into a result value. Although this result value is usually not used, it can then be used by another expression.

Chaining assignments or nesting assignments in other expressions can result in surprising behavior. For this reason, some JavaScript style guides discourage chaining or nesting assignments . Nevertheless, assignment chaining and nesting may occur sometimes, so it is important to be able to understand how they work.

By chaining or nesting an assignment expression, its result can itself be assigned to another variable. It can be logged, it can be put inside an array literal or function call, and so on.

The evaluation result matches the expression to the right of the = sign in the "Meaning" column of the table above. That means that x = f() evaluates into whatever f() 's result is, x += f() evaluates into the resulting sum x + f() , x **= f() evaluates into the resulting power x ** f() , and so on.

In the case of logical assignments, x &&= f() , x ||= f() , and x ??= f() , the return value is that of the logical operation without the assignment, so x && f() , x || f() , and x ?? f() , respectively.

When chaining these expressions without parentheses or other grouping operators like array literals, the assignment expressions are grouped right to left (they are right-associative ), but they are evaluated left to right .

Note that, for all assignment operators other than = itself, the resulting values are always based on the operands' values before the operation.

For example, assume that the following functions f and g and the variables x and y have been declared:

Consider these three examples:

Evaluation example 1

y = x = f() is equivalent to y = (x = f()) , because the assignment operator = is right-associative . However, it evaluates from left to right:

• The y on this assignment's left-hand side evaluates into a reference to the variable named y .
• The x on this assignment's left-hand side evaluates into a reference to the variable named x .
• The function call f() prints "F!" to the console and then evaluates to the number 2 .
• That 2 result from f() is assigned to x .
• The assignment expression x = f() has now finished evaluating; its result is the new value of x , which is 2 .
• That 2 result in turn is also assigned to y .
• The assignment expression y = x = f() has now finished evaluating; its result is the new value of y – which happens to be 2 . x and y are assigned to 2 , and the console has printed "F!".

Evaluation example 2

y = [ f(), x = g() ] also evaluates from left to right:

• The y on this assignment's left-hand evaluates into a reference to the variable named y .
• The function call g() prints "G!" to the console and then evaluates to the number 3 .
• That 3 result from g() is assigned to x .
• The assignment expression x = g() has now finished evaluating; its result is the new value of x , which is 3 . That 3 result becomes the next element in the inner array literal (after the 2 from the f() ).
• The inner array literal [ f(), x = g() ] has now finished evaluating; its result is an array with two values: [ 2, 3 ] .
• That [ 2, 3 ] array is now assigned to y .
• The assignment expression y = [ f(), x = g() ] has now finished evaluating; its result is the new value of y – which happens to be [ 2, 3 ] . x is now assigned to 3 , y is now assigned to [ 2, 3 ] , and the console has printed "F!" then "G!".

Evaluation example 3

x[f()] = g() also evaluates from left to right. (This example assumes that x is already assigned to some object. For more information about objects, read Working with Objects .)

• The x in this property access evaluates into a reference to the variable named x .
• Then the function call f() prints "F!" to the console and then evaluates to the number 2 .
• The x[f()] property access on this assignment has now finished evaluating; its result is a variable property reference: x[2] .
• Then the function call g() prints "G!" to the console and then evaluates to the number 3 .
• That 3 is now assigned to x[2] . (This step will succeed only if x is assigned to an object .)
• The assignment expression x[f()] = g() has now finished evaluating; its result is the new value of x[2] – which happens to be 3 . x[2] is now assigned to 3 , and the console has printed "F!" then "G!".

Avoid assignment chains

Chaining assignments or nesting assignments in other expressions can result in surprising behavior. For this reason, chaining assignments in the same statement is discouraged .

In particular, putting a variable chain in a const , let , or var statement often does not work. Only the outermost/leftmost variable would get declared; other variables within the assignment chain are not declared by the const / let / var statement. For example:

This statement seemingly declares the variables x , y , and z . However, it only actually declares the variable z . y and x are either invalid references to nonexistent variables (in strict mode ) or, worse, would implicitly create global variables for x and y in sloppy mode .

A comparison operator compares its operands and returns a logical value based on whether the comparison is true. The operands can be numerical, string, logical, or object values. Strings are compared based on standard lexicographical ordering, using Unicode values. In most cases, if the two operands are not of the same type, JavaScript attempts to convert them to an appropriate type for the comparison. This behavior generally results in comparing the operands numerically. The sole exceptions to type conversion within comparisons involve the === and !== operators, which perform strict equality and inequality comparisons. These operators do not attempt to convert the operands to compatible types before checking equality. The following table describes the comparison operators in terms of this sample code:

Note: => is not a comparison operator but rather is the notation for Arrow functions .

An arithmetic operator takes numerical values (either literals or variables) as their operands and returns a single numerical value. The standard arithmetic operators are addition ( + ), subtraction ( - ), multiplication ( * ), and division ( / ). These operators work as they do in most other programming languages when used with floating point numbers (in particular, note that division by zero produces Infinity ). For example:

In addition to the standard arithmetic operations ( + , - , * , / ), JavaScript provides the arithmetic operators listed in the following table:

A bitwise operator treats their operands as a set of 32 bits (zeros and ones), rather than as decimal, hexadecimal, or octal numbers. For example, the decimal number nine has a binary representation of 1001. Bitwise operators perform their operations on such binary representations, but they return standard JavaScript numerical values.

The following table summarizes JavaScript's bitwise operators.

Bitwise logical operators

Conceptually, the bitwise logical operators work as follows:

• The operands are converted to thirty-two-bit integers and expressed by a series of bits (zeros and ones). Numbers with more than 32 bits get their most significant bits discarded. For example, the following integer with more than 32 bits will be converted to a 32-bit integer: Before: 1110 0110 1111 1010 0000 0000 0000 0110 0000 0000 0001 After: 1010 0000 0000 0000 0110 0000 0000 0001
• Each bit in the first operand is paired with the corresponding bit in the second operand: first bit to first bit, second bit to second bit, and so on.
• The operator is applied to each pair of bits, and the result is constructed bitwise.

For example, the binary representation of nine is 1001, and the binary representation of fifteen is 1111. So, when the bitwise operators are applied to these values, the results are as follows:

Note that all 32 bits are inverted using the Bitwise NOT operator, and that values with the most significant (left-most) bit set to 1 represent negative numbers (two's-complement representation). ~x evaluates to the same value that -x - 1 evaluates to.

Bitwise shift operators

The bitwise shift operators take two operands: the first is a quantity to be shifted, and the second specifies the number of bit positions by which the first operand is to be shifted. The direction of the shift operation is controlled by the operator used.

Shift operators convert their operands to thirty-two-bit integers and return a result of either type Number or BigInt : specifically, if the type of the left operand is BigInt , they return BigInt ; otherwise, they return Number .

The shift operators are listed in the following table.

Logical operators are typically used with Boolean (logical) values; when they are, they return a Boolean value. However, the && and || operators actually return the value of one of the specified operands, so if these operators are used with non-Boolean values, they may return a non-Boolean value. The logical operators are described in the following table.

Examples of expressions that can be converted to false are those that evaluate to null, 0, NaN, the empty string (""), or undefined.

The following code shows examples of the && (logical AND) operator.

The following code shows examples of the || (logical OR) operator.

The following code shows examples of the ! (logical NOT) operator.

Short-circuit evaluation

As logical expressions are evaluated left to right, they are tested for possible "short-circuit" evaluation using the following rules:

• false && anything is short-circuit evaluated to false.
• true || anything is short-circuit evaluated to true.

The rules of logic guarantee that these evaluations are always correct. Note that the anything part of the above expressions is not evaluated, so any side effects of doing so do not take effect.

Note that for the second case, in modern code you can use the Nullish coalescing operator ( ?? ) that works like || , but it only returns the second expression, when the first one is " nullish ", i.e. null or undefined . It is thus the better alternative to provide defaults, when values like '' or 0 are valid values for the first expression, too.

Most operators that can be used between numbers can be used between BigInt values as well.

One exception is unsigned right shift ( >>> ) , which is not defined for BigInt values. This is because a BigInt does not have a fixed width, so technically it does not have a "highest bit".

BigInts and numbers are not mutually replaceable — you cannot mix them in calculations.

This is because BigInt is neither a subset nor a superset of numbers. BigInts have higher precision than numbers when representing large integers, but cannot represent decimals, so implicit conversion on either side might lose precision. Use explicit conversion to signal whether you wish the operation to be a number operation or a BigInt one.

You can compare BigInts with numbers.

In addition to the comparison operators, which can be used on string values, the concatenation operator (+) concatenates two string values together, returning another string that is the union of the two operand strings.

For example,

The shorthand assignment operator += can also be used to concatenate strings.

The conditional operator is the only JavaScript operator that takes three operands. The operator can have one of two values based on a condition. The syntax is:

If condition is true, the operator has the value of val1 . Otherwise it has the value of val2 . You can use the conditional operator anywhere you would use a standard operator.

This statement assigns the value "adult" to the variable status if age is eighteen or more. Otherwise, it assigns the value "minor" to status .

The comma operator ( , ) evaluates both of its operands and returns the value of the last operand. This operator is primarily used inside a for loop, to allow multiple variables to be updated each time through the loop. It is regarded bad style to use it elsewhere, when it is not necessary. Often two separate statements can and should be used instead.

For example, if a is a 2-dimensional array with 10 elements on a side, the following code uses the comma operator to update two variables at once. The code prints the values of the diagonal elements in the array:

A unary operation is an operation with only one operand.

The delete operator deletes an object's property. The syntax is:

where object is the name of an object, property is an existing property, and propertyKey is a string or symbol referring to an existing property.

If the delete operator succeeds, it removes the property from the object. Trying to access it afterwards will yield undefined . The delete operator returns true if the operation is possible; it returns false if the operation is not possible.

Deleting array elements

Since arrays are just objects, it's technically possible to delete elements from them. This is, however, regarded as a bad practice — try to avoid it. When you delete an array property, the array length is not affected and other elements are not re-indexed. To achieve that behavior, it is much better to just overwrite the element with the value undefined . To actually manipulate the array, use the various array methods such as splice .

The typeof operator returns a string indicating the type of the unevaluated operand. operand is the string, variable, keyword, or object for which the type is to be returned. The parentheses are optional.

Suppose you define the following variables:

The typeof operator returns the following results for these variables:

For the keywords true and null , the typeof operator returns the following results:

For a number or string, the typeof operator returns the following results:

For property values, the typeof operator returns the type of value the property contains:

For methods and functions, the typeof operator returns results as follows:

For predefined objects, the typeof operator returns results as follows:

The void operator specifies an expression to be evaluated without returning a value. expression is a JavaScript expression to evaluate. The parentheses surrounding the expression are optional, but it is good style to use them to avoid precedence issues.

A relational operator compares its operands and returns a Boolean value based on whether the comparison is true.

The in operator returns true if the specified property is in the specified object. The syntax is:

where propNameOrNumber is a string, numeric, or symbol expression representing a property name or array index, and objectName is the name of an object.

The following examples show some uses of the in operator.

The instanceof operator returns true if the specified object is of the specified object type. The syntax is:

where objectName is the name of the object to compare to objectType , and objectType is an object type, such as Date or Array .

Use instanceof when you need to confirm the type of an object at runtime. For example, when catching exceptions, you can branch to different exception-handling code depending on the type of exception thrown.

For example, the following code uses instanceof to determine whether theDay is a Date object. Because theDay is a Date object, the statements in the if statement execute.

Basic expressions

All operators eventually operate on one or more basic expressions. These basic expressions include identifiers and literals , but there are a few other kinds as well. They are briefly introduced below, and their semantics are described in detail in their respective reference sections.

Use the this keyword to refer to the current object. In general, this refers to the calling object in a method. Use this either with the dot or the bracket notation:

Suppose a function called validate validates an object's value property, given the object and the high and low values:

You could call validate in each form element's onChange event handler, using this to pass it to the form element, as in the following example:

Grouping operator

The grouping operator ( ) controls the precedence of evaluation in expressions. For example, you can override multiplication and division first, then addition and subtraction to evaluate addition first.

You can use the new operator to create an instance of a user-defined object type or of one of the built-in object types. Use new as follows:

The super keyword is used to call functions on an object's parent. It is useful with classes to call the parent constructor, for example.

#21 - Compound Assignment Operators

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freeCodeCamp Challenge Guide: Compound Assignment With Augmented Addition

Compound assignment with augmented addition.

Computers read from left to right. So, using the ‘+=’ operator means that the variable is added with the right number, then the variable is assigned to the sum. Like so:

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C# Compound Assignment (e.g. +=, -=, etc.) "Exceptions" [closed]

I'm reading a book on C#, and it has this to say about compound assignments (e.g. +=, -=, *=, /=, <<=, >>=):

A subtle exception to this rule is with events, which we describe in Chapter 4: the += and -= operators here are treated specially and map to the event's add and removed accessors.

Can anyone explain what that means in plain English? I'm not to Chapter 4 yet.

• compound-assignment

• It is what it says. For event , those operators act special - they call the add and remove methods, respectively. –  user166390 Feb 5, 2013 at 6:04
• 3 You can always skip to Chapter 4, take a peek, then return to where you left off. Edit: wait a minute, it says "we described in Chapter 4", in the past tense. Doesn't that imply you're in a later chapter? Did you skip past Chapter 4, or did the book get its tenses mixed up? ಠ_ಠ –  BoltClock Feb 5, 2013 at 6:04
• @pst What is the "event" that is taking place? –  TimFoolery Feb 5, 2013 at 6:06
• 2 Okay, I'm throwing in my -1 now. Please read supplied links. I don't add them for my sake. –  user166390 Feb 5, 2013 at 6:06
• 2 @Michael: Ah, that explains. That said, I do what I say in my comment whenever the book doesn't bother explaining new concepts to me in context, and/or it points to the relevant chapter instead. Programming books are the kind where you don't have to read them from start to finish - you can jump between chapters anytime you wish :) –  BoltClock Feb 5, 2013 at 6:19

3 Answers 3

Normally a += would add the expression/variable on the right hand side to the one on the left and assign the result to the left hand side.

But in case the left hand side of the expression with a += is an event, then this is not the case, but it would be the event handler on the right hand side, which is added to the list of event handlers for that event.

• Oh, ok. :) It's an overloaded operator that takes on a new meaning when the LHS is an event. Got it. Thank you! :) –  TimFoolery Feb 5, 2013 at 6:12

It simply means += is attaching an event method to e.g. a control instead of addition (e.g. arithmetic addition)

see the difference?

There is a notion of delegate in C# which can point a Method. You can think of events like a special type of delegates. You can add (or remove ) many methods to an event. It allows you to execute specified methods when a specific event occurs.

A simple example when you delete a file that shows delete result both on Console and MessageBox.

Not the answer you're looking for? Browse other questions tagged c# events compound-assignment or ask your own question .

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What Is Compound Interest?

When it comes to calculating interest, there are two basic choices: simple and compound. Simple interest simply means a set percentage of the principal amount every year.

For example, if you invest $1,000 at 5% simple interest for 10 years, you can expect to receive $50 in interest every year for the next decade. No more, no less. In the investment world, bonds are an example of an investment that typically pays simple interest.

What is compound interest?

On the other hand, compound interest is what you get when you reinvest your earnings, which then also earn interest. Compound interest essentially means "interest on the interest" and is why many investors are so successful.

Think of it this way. Let's say you invest $1,000 at 5% interest. After the first year, you receive a $50 interest payment, but instead of receiving it in cash, you reinvest the interest you earned at the same 5% rate. For the second year, your interest would be calculated on a $1,050 investment, which comes to $52.50. If you reinvest that, your third-year interest would be calculated on a $1,102.50 balance.

You get the idea. Compound interest means your principal gets larger over time and will generate larger and larger interest payments. The difference between simple and compound interest can be massive. Take a look at the difference on a $10,000 investment portfolio at 10% interest over time:

Note that 10% is, roughly, the long-term annualized return of the S&P 500 . It was 9.65% for the 30-year period through 2022. Returns like this, compounded over long periods, can result in some pretty impressive performances.

It's also worth mentioning that there's a very similar concept known as  cumulative interest. Cumulative interest refers to the sum of the interest payments made, but it typically refers to payments made on a loan. For example, the cumulative interest on a 30-year mortgage would be how much you paid toward interest over the 30-year loan term.

How to calculate compound interest

How compound interest is calculated.

Compound interest is calculated by applying an exponential growth factor to the interest rate or rate of return you're using. The good news is that there are plenty of excellent calculators that will do the math for you.

Below is a mathematical formula you could use for calculating compound interest over a certain period:

With "A" as the final amount, here's what all the other variables mean:

• Principal (P): The starting balance on which interest is calculated. For example, if you decide to invest $10,000 for five years, that amount would be your principal for the purposes of calculating compound interest.
• Interest rate (or expected rate of return in investing) expressed as a decimal (r): For calculation purposes, if you expect your investments to grow at an average rate of 7% per year, you would use 0.07 here.
• Compounding frequency (n): How frequently you're adding interest to the principal. Using the example of 7% interest, if we were to use annual compounding, you would simply add 7% to the principal once per year. On the other hand, semiannual compounding would involve applying half of that amount (3.5%) twice a year. Other common compounding frequencies include quarterly (every three months), monthly, weekly, or daily.
• Time (T): The total time in years. In other words, if you're investing for 30 months, be sure to use 2.5 years in the formula.

Compounding frequency

Compounding frequency and why it matters.

In the previous example, we used annual compounding, meaning the interest is calculated once per year. In practice, compound interest is often calculated more frequently. For example, your savings account may calculate interest monthly. Common compounding intervals are quarterly, monthly, and daily, but many other possible intervals could be used.

The compounding frequency makes a difference. All other factors being equal, more frequent compounding leads to faster growth. For instance, the table below shows the growth of $10,000 at 8% interest compounded at several frequencies:

Example of calculating compound interest

As a basic example, let's say you're investing $20,000 at 5% interest compounded quarterly for 20 years. In this case, "n" would be four, as quarterly compounding occurs four times per year.

Based on this information, we can calculate the investment's final value after 20 years like this:

Compound earnings vs. compound interest

You may hear the terms compound interest and compound earnings used interchangeably, especially when discussing investment returns. However, there's a subtle difference.

Specifically, compound earnings refers to the compounding effects of  both interest payments and dividends, as well as appreciation in the value of the investment itself. In other words, it's more of an all-in-one term to describe investment returns that aren't entirely interest.

For example, if a stock investment paid you a 4% dividend yield and the stock itself increased in value by 5%, you'd have total earnings of 9% for the year. When these dividends and price gains compound over time, it is a form of compound earnings and not interest, as not all of the gains come from payments to you.

In a nutshell, long-term returns from stocks, exchange-traded funds (ETFs) , or mutual funds are technically called compound earnings. However, it can still be calculated in the same manner if you know your expected rate of return.

Related investing topics

Accounts that earn compounding interest.

Interest compounds when interest payments also earn interest. Learn how to get compounding interest working for your portfolio.

What Is a Good Return on Investment?

You invest to get a return. So what makes a good ROI?

Municipal Bonds

Municipalities issue bonds that could be a great investment. How do they work?

Importance of compound interest

Why compound interest is such an important concept for investors.

Compound interest is the phenomenon that allows seemingly small amounts of money to grow into large amounts over time. To take full advantage of the power of compound interest, investments must be allowed to grow and compound for long periods.

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