define variable assignment operator

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Variables and Assignment ¶

When programming, it is useful to be able to store information in variables. A variable is a string of characters and numbers associated with a piece of information. The assignment operator , denoted by the “=” symbol, is the operator that is used to assign values to variables in Python. The line x=1 takes the known value, 1, and assigns that value to the variable with name “x”. After executing this line, this number will be stored into this variable. Until the value is changed or the variable deleted, the character x behaves like the value 1.

TRY IT! Assign the value 2 to the variable y. Multiply y by 3 to show that it behaves like the value 2.

A variable is more like a container to store the data in the computer’s memory, the name of the variable tells the computer where to find this value in the memory. For now, it is sufficient to know that the notebook has its own memory space to store all the variables in the notebook. As a result of the previous example, you will see the variable “x” and “y” in the memory. You can view a list of all the variables in the notebook using the magic command %whos .

TRY IT! List all the variables in this notebook

Note that the equal sign in programming is not the same as a truth statement in mathematics. In math, the statement x = 2 declares the universal truth within the given framework, x is 2 . In programming, the statement x=2 means a known value is being associated with a variable name, store 2 in x. Although it is perfectly valid to say 1 = x in mathematics, assignments in Python always go left : meaning the value to the right of the equal sign is assigned to the variable on the left of the equal sign. Therefore, 1=x will generate an error in Python. The assignment operator is always last in the order of operations relative to mathematical, logical, and comparison operators.

TRY IT! The mathematical statement x=x+1 has no solution for any value of x . In programming, if we initialize the value of x to be 1, then the statement makes perfect sense. It means, “Add x and 1, which is 2, then assign that value to the variable x”. Note that this operation overwrites the previous value stored in x .

There are some restrictions on the names variables can take. Variables can only contain alphanumeric characters (letters and numbers) as well as underscores. However, the first character of a variable name must be a letter or underscores. Spaces within a variable name are not permitted, and the variable names are case-sensitive (e.g., x and X will be considered different variables).

TIP! Unlike in pure mathematics, variables in programming almost always represent something tangible. It may be the distance between two points in space or the number of rabbits in a population. Therefore, as your code becomes increasingly complicated, it is very important that your variables carry a name that can easily be associated with what they represent. For example, the distance between two points in space is better represented by the variable dist than x , and the number of rabbits in a population is better represented by nRabbits than y .

Note that when a variable is assigned, it has no memory of how it was assigned. That is, if the value of a variable, y , is constructed from other variables, like x , reassigning the value of x will not change the value of y .

EXAMPLE: What value will y have after the following lines of code are executed?

WARNING! You can overwrite variables or functions that have been stored in Python. For example, the command help = 2 will store the value 2 in the variable with name help . After this assignment help will behave like the value 2 instead of the function help . Therefore, you should always be careful not to give your variables the same name as built-in functions or values.

TIP! Now that you know how to assign variables, it is important that you learn to never leave unassigned commands. An unassigned command is an operation that has a result, but that result is not assigned to a variable. For example, you should never use 2+2 . You should instead assign it to some variable x=2+2 . This allows you to “hold on” to the results of previous commands and will make your interaction with Python must less confusing.

You can clear a variable from the notebook using the del function. Typing del x will clear the variable x from the workspace. If you want to remove all the variables in the notebook, you can use the magic command %reset .

In mathematics, variables are usually associated with unknown numbers; in programming, variables are associated with a value of a certain type. There are many data types that can be assigned to variables. A data type is a classification of the type of information that is being stored in a variable. The basic data types that you will utilize throughout this book are boolean, int, float, string, list, tuple, dictionary, set. A formal description of these data types is given in the following sections.

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C++ functions, c++ classes, c++ data s tructures, c++ reference, c++ examples, c++ assignment operators, assignment operators.

Assignment operators are used to assign values to variables.

In the example below, we use the assignment operator ( = ) to assign the value 10 to a variable called x :

The addition assignment operator ( += ) adds a value to a variable:

A list of all assignment operators:

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Variables in Python

Table of Contents

Variable Assignment

Variable types in python, object references, object identity, variable names, reserved words (keywords).

Watch Now This tutorial has a related video course created by the Real Python team. Watch it together with the written tutorial to deepen your understanding: Variables in Python

In the previous tutorial on Basic Data Types in Python , you saw how values of various Python data types can be created. But so far, all the values shown have been literal or constant values:

If you’re writing more complex code, your program will need data that can change as program execution proceeds.

Here’s what you’ll learn in this tutorial: You will learn how every item of data in a Python program can be described by the abstract term object , and you’ll learn how to manipulate objects using symbolic names called variables .

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Test your understanding of Python variables and object references.

Think of a variable as a name attached to a particular object. In Python, variables need not be declared or defined in advance, as is the case in many other programming languages. To create a variable, you just assign it a value and then start using it. Assignment is done with a single equals sign ( = ):

This is read or interpreted as “ n is assigned the value 300 .” Once this is done, n can be used in a statement or expression, and its value will be substituted:

Just as a literal value can be displayed directly from the interpreter prompt in a REPL session without the need for print() , so can a variable:

Later, if you change the value of n and use it again, the new value will be substituted instead:

Python also allows chained assignment, which makes it possible to assign the same value to several variables simultaneously:

The chained assignment above assigns 300 to the variables a , b , and c simultaneously.

In many programming languages, variables are statically typed. That means a variable is initially declared to have a specific data type, and any value assigned to it during its lifetime must always have that type.

Variables in Python are not subject to this restriction. In Python, a variable may be assigned a value of one type and then later re-assigned a value of a different type:

What is actually happening when you make a variable assignment? This is an important question in Python, because the answer differs somewhat from what you’d find in many other programming languages.

Python is a highly object-oriented language . In fact, virtually every item of data in a Python program is an object of a specific type or class. (This point will be reiterated many times over the course of these tutorials.)

Consider this code:

When presented with the statement print(300) , the interpreter does the following:

• Creates an integer object
• Gives it the value 300
• Displays it to the console

You can see that an integer object is created using the built-in type() function:

A Python variable is a symbolic name that is a reference or pointer to an object. Once an object is assigned to a variable, you can refer to the object by that name. But the data itself is still contained within the object.

For example:

This assignment creates an integer object with the value 300 and assigns the variable n to point to that object.

The following code verifies that n points to an integer object:

Now consider the following statement:

What happens when it is executed? Python does not create another object. It simply creates a new symbolic name or reference, m , which points to the same object that n points to.

Next, suppose you do this:

Now Python creates a new integer object with the value 400 , and m becomes a reference to it.

Lastly, suppose this statement is executed next:

Now Python creates a string object with the value "foo" and makes n reference that.

There is no longer any reference to the integer object 300 . It is orphaned, and there is no way to access it.

Tutorials in this series will occasionally refer to the lifetime of an object. An object’s life begins when it is created, at which time at least one reference to it is created. During an object’s lifetime, additional references to it may be created, as you saw above, and references to it may be deleted as well. An object stays alive, as it were, so long as there is at least one reference to it.

When the number of references to an object drops to zero, it is no longer accessible. At that point, its lifetime is over. Python will eventually notice that it is inaccessible and reclaim the allocated memory so it can be used for something else. In computer lingo, this process is referred to as garbage collection .

In Python, every object that is created is given a number that uniquely identifies it. It is guaranteed that no two objects will have the same identifier during any period in which their lifetimes overlap. Once an object’s reference count drops to zero and it is garbage collected, as happened to the 300 object above, then its identifying number becomes available and may be used again.

The built-in Python function id() returns an object’s integer identifier. Using the id() function, you can verify that two variables indeed point to the same object:

After the assignment m = n , m and n both point to the same object, confirmed by the fact that id(m) and id(n) return the same number. Once m is reassigned to 400 , m and n point to different objects with different identities.

Deep Dive: Caching Small Integer Values From what you now know about variable assignment and object references in Python, the following probably won’t surprise you: Python >>> m = 300 >>> n = 300 >>> id ( m ) 60062304 >>> id ( n ) 60062896 Copied! With the statement m = 300 , Python creates an integer object with the value 300 and sets m as a reference to it. n is then similarly assigned to an integer object with value 300 —but not the same object. Thus, they have different identities, which you can verify from the values returned by id() . But consider this: Python >>> m = 30 >>> n = 30 >>> id ( m ) 1405569120 >>> id ( n ) 1405569120 Copied! Here, m and n are separately assigned to integer objects having value 30 . But in this case, id(m) and id(n) are identical! For purposes of optimization, the interpreter creates objects for the integers in the range [-5, 256] at startup, and then reuses them during program execution. Thus, when you assign separate variables to an integer value in this range, they will actually reference the same object.

The examples you have seen so far have used short, terse variable names like m and n . But variable names can be more verbose. In fact, it is usually beneficial if they are because it makes the purpose of the variable more evident at first glance.

Officially, variable names in Python can be any length and can consist of uppercase and lowercase letters ( A-Z , a-z ), digits ( 0-9 ), and the underscore character ( _ ). An additional restriction is that, although a variable name can contain digits, the first character of a variable name cannot be a digit.

Note: One of the additions to Python 3 was full Unicode support , which allows for Unicode characters in a variable name as well. You will learn about Unicode in greater depth in a future tutorial.

For example, all of the following are valid variable names:

But this one is not, because a variable name can’t begin with a digit:

Note that case is significant. Lowercase and uppercase letters are not the same. Use of the underscore character is significant as well. Each of the following defines a different variable:

There is nothing stopping you from creating two different variables in the same program called age and Age , or for that matter agE . But it is probably ill-advised. It would certainly be likely to confuse anyone trying to read your code, and even you yourself, after you’d been away from it awhile.

It is worthwhile to give a variable a name that is descriptive enough to make clear what it is being used for. For example, suppose you are tallying the number of people who have graduated college. You could conceivably choose any of the following:

All of them are probably better choices than n , or ncg , or the like. At least you can tell from the name what the value of the variable is supposed to represent.

On the other hand, they aren’t all necessarily equally legible. As with many things, it is a matter of personal preference, but most people would find the first two examples, where the letters are all shoved together, to be harder to read, particularly the one in all capital letters. The most commonly used methods of constructing a multi-word variable name are the last three examples:

• Example: numberOfCollegeGraduates
• Example: NumberOfCollegeGraduates
• Example: number_of_college_graduates

Programmers debate hotly, with surprising fervor, which of these is preferable. Decent arguments can be made for all of them. Use whichever of the three is most visually appealing to you. Pick one and use it consistently.

You will see later that variables aren’t the only things that can be given names. You can also name functions, classes, modules, and so on. The rules that apply to variable names also apply to identifiers, the more general term for names given to program objects.

The Style Guide for Python Code , also known as PEP 8 , contains Naming Conventions that list suggested standards for names of different object types. PEP 8 includes the following recommendations:

• Snake Case should be used for functions and variable names.
• Pascal Case should be used for class names. (PEP 8 refers to this as the “CapWords” convention.)

There is one more restriction on identifier names. The Python language reserves a small set of keywords that designate special language functionality. No object can have the same name as a reserved word.

In Python 3.6, there are 33 reserved keywords:

You can see this list any time by typing help("keywords") to the Python interpreter. Reserved words are case-sensitive and must be used exactly as shown. They are all entirely lowercase, except for False , None , and True .

Trying to create a variable with the same name as any reserved word results in an error:

This tutorial covered the basics of Python variables , including object references and identity, and naming of Python identifiers.

You now have a good understanding of some of Python’s data types and know how to create variables that reference objects of those types.

Next, you will see how to combine data objects into expressions involving various operations .

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Assignment (=)

The assignment ( = ) operator is used to assign a value to a variable or property. The assignment expression itself has a value, which is the assigned value. This allows multiple assignments to be chained in order to assign a single value to multiple variables.

A valid assignment target, including an identifier or a property accessor . It can also be a destructuring assignment pattern .

An expression specifying the value to be assigned to x .

Return value

The value of y .

Thrown in strict mode if assigning to an identifier that is not declared in the scope.

Thrown in strict mode if assigning to a property that is not modifiable .

Description

The assignment operator is completely different from the equals ( = ) sign used as syntactic separators in other locations, which include:

• Initializers of var , let , and const declarations
• Default values of destructuring
• Default parameters
• Initializers of class fields

All these places accept an assignment expression on the right-hand side of the = , so if you have multiple equals signs chained together:

This is equivalent to:

Which means y must be a pre-existing variable, and x is a newly declared const variable. y is assigned the value 5 , and x is initialized with the value of the y = 5 expression, which is also 5 . If y is not a pre-existing variable, a global variable y is implicitly created in non-strict mode , or a ReferenceError is thrown in strict mode. To declare two variables within the same declaration, use:

Simple assignment and chaining

Value of assignment expressions.

The assignment expression itself evaluates to the value of the right-hand side, so you can log the value and assign to a variable at the same time.

Unqualified identifier assignment

The global object sits at the top of the scope chain. When attempting to resolve a name to a value, the scope chain is searched. This means that properties on the global object are conveniently visible from every scope, without having to qualify the names with globalThis. or window. or global. .

Because the global object has a String property ( Object.hasOwn(globalThis, "String") ), you can use the following code:

So the global object will ultimately be searched for unqualified identifiers. You don't have to type globalThis.String ; you can just type the unqualified String . To make this feature more conceptually consistent, assignment to unqualified identifiers will assume you want to create a property with that name on the global object (with globalThis. omitted), if there is no variable of the same name declared in the scope chain.

In strict mode , assignment to an unqualified identifier in strict mode will result in a ReferenceError , to avoid the accidental creation of properties on the global object.

Note that the implication of the above is that, contrary to popular misinformation, JavaScript does not have implicit or undeclared variables. It just conflates the global object with the global scope and allows omitting the global object qualifier during property creation.

Assignment with destructuring

The left-hand side of can also be an assignment pattern. This allows assigning to multiple variables at once.

For more information, see Destructuring assignment .

Specifications

Browser compatibility

BCD tables only load in the browser with JavaScript enabled. Enable JavaScript to view data.

• Assignment operators in the JS guide
• Destructuring assignment

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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1.4 — Variable assignment and initialization

There are 6 basic ways to initialize variables in C++:

Much like copy assignment, this copies the value on the right-hand side of the equals into the variable being created on the left-hand side. In the above snippet, variable width will be initialized with value 5 .

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Assignment operators (C# reference)

• 11 contributors

The assignment operator = assigns the value of its right-hand operand to a variable, a property , or an indexer element given by its left-hand operand. The result of an assignment expression is the value assigned to the left-hand operand. The type of the right-hand operand must be the same as the type of the left-hand operand or implicitly convertible to it.

The assignment operator = is right-associative, that is, an expression of the form

is evaluated as

The following example demonstrates the usage of the assignment operator with a local variable, a property, and an indexer element as its left-hand operand:

The left-hand operand of an assignment receives the value of the right-hand operand. When the operands are of value types , assignment copies the contents of the right-hand operand. When the operands are of reference types , assignment copies the reference to the object.

This is called value assignment : the value is assigned.

ref assignment

Ref assignment = ref makes its left-hand operand an alias to the right-hand operand, as the following example demonstrates:

In the preceding example, the local reference variable arrayElement is initialized as an alias to the first array element. Then, it's ref reassigned to refer to the last array element. As it's an alias, when you update its value with an ordinary assignment operator = , the corresponding array element is also updated.

The left-hand operand of ref assignment can be a local reference variable , a ref field , and a ref , out , or in method parameter. Both operands must be of the same type.

Compound assignment

For a binary operator op , a compound assignment expression of the form

is equivalent to

except that x is only evaluated once.

Compound assignment is supported by arithmetic , Boolean logical , and bitwise logical and shift operators.

Null-coalescing assignment

You can use the null-coalescing assignment operator ??= to assign the value of its right-hand operand to its left-hand operand only if the left-hand operand evaluates to null . For more information, see the ?? and ??= operators article.

Operator overloadability

A user-defined type can't overload the assignment operator. However, a user-defined type can define an implicit conversion to another type. That way, the value of a user-defined type can be assigned to a variable, a property, or an indexer element of another type. For more information, see User-defined conversion operators .

A user-defined type can't explicitly overload a compound assignment operator. However, if a user-defined type overloads a binary operator op , the op= operator, if it exists, is also implicitly overloaded.

C# language specification

For more information, see the Assignment operators section of the C# language specification .

• C# operators and expressions
• ref keyword
• Use compound assignment (style rules IDE0054 and IDE0074)

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What are Operators in Programming?

Operators in programming are essential symbols that perform operations on variables and values , enabling tasks like arithmetic calculations, logical comparisons, and bitwise manipulations. In this article, we will learn about the basics of operators and their types.

Operators in Programming

Table of Content

• Types of Operators in Programming
• Operator Precedence and Associativity in Programming
• Frequently Asked Questions (FAQs) related to Programming Operators

Operators in programming are symbols or keywords that represent computations or actions performed on operands. Operands can be variables , constants , or values , and the combination of operators and operands form expressions. Operators play a crucial role in performing various tasks, such as arithmetic calculations, logical comparisons, bitwise operations, etc.

Types of Operators in Programming:

Here are some common types of operators:

• Arithmetic Operators: Perform basic arithmetic operations on numeric values. Examples: + (addition), – (subtraction), * (multiplication), / (division), % (modulo).
• Comparison Operators: Compare two values and return a Boolean result (true or false). Examples: == (equal to), != (not equal to), < (less than), > (greater than), <= (less than or equal to), >= (greater than or equal to).
• Logical Operators: Perform logical operations on Boolean values. Examples: && (logical AND), || (logical OR), ! (logical NOT).
• Assignment Operators: Assign values to variables. Examples: = (assign), += (add and assign), -=, *= (multiply and assign), /=, %=.
• Increment and Decrement Operators: Increase or decrease the value of a variable by 1. Examples: ++ (increment), — (decrement).
• Bitwise Operators: Perform operations on individual bits of binary representations of numbers. Examples: & (bitwise AND), | (bitwise OR), ^ (bitwise XOR), ~ (bitwise NOT), << (left shift), >> (right shift).

These operators provide the building blocks for creating complex expressions and performing diverse operations in programming languages. Understanding their usage is crucial for writing efficient and expressive code.

Arithmetic Operators in Programming:

Arithmetic operators in programming are fundamental components of programming languages, enabling the manipulation of numeric values for various computational tasks. Here’s an elaboration on the key arithmetic operators:

Comparison Operators in Programming:

Comparison operators in programming are used to compare two values or expressions and return a Boolean result indicating the relationship between them. These operators play a crucial role in decision-making and conditional statements. Here are the common comparison operators:

These operators are extensively used in conditional statements, loops, and decision-making constructs to control the flow of a program based on the relationship between variables or values. Understanding comparison operators is crucial for creating logical and effective algorithms in programming.

Logical Operators in Programming:

Logical operators in programming are used to perform logical operations on Boolean values . These operators are crucial for combining or manipulating conditions and controlling the flow of a program based on logical expressions. Here are the common logical operators:

These logical operators are frequently used in conditional statements (if, else if, else), loops, and decision-making constructs to create complex conditions based on multiple Boolean expressions. Understanding how to use logical operators is essential for designing effective and readable control flow in programming.

Assignment Operators in Programming:

Assignment operators in programming are used to assign values to variables. They are essential for storing and updating data within a program. Here are common assignment operators:

Assignment operators are fundamental for updating variable values, especially in loops and mathematical computations, contributing to the dynamic nature of programming. Understanding how to use assignment operators is essential for effective variable manipulation in a program.

Increment and Decrement Operators in Programming:

Increment and decrement operators in programming are used to increase or decrease the value of a variable by 1, respectively. They are shorthand notations for common operations and are particularly useful in loops. Here are the two types:

These operators are frequently employed in loops, especially for iterating through arrays or performing repetitive tasks. Their concise syntax enhances code readability and expressiveness.

Bitwise Operators in Programming:

Bitwise operators in programming perform operations at the bit level , manipulating individual bits of binary representations of numbers. These operators are often used in low-level programming, such as embedded systems and device drivers. Here are the common bitwise operators:

Bitwise operators are useful in scenarios where direct manipulation of binary representations or specific bit patterns is required, such as optimizing certain algorithms or working with hardware interfaces. Understanding bitwise operations is essential for low-level programming tasks.

Operator Precedence and Associativity in Programming :

Operator Precedence is a rule that determines the order in which operators are evaluated in an expression. It defines which operators take precedence over others when they are combined in the same expression. Operators with higher precedence are evaluated before operators with lower precedence. Parentheses can be used to override the default precedence and explicitly specify the order of evaluation.

Operator Associativity is a rule that determines the grouping of operators with the same precedence in an expression when they appear consecutively. It specifies the direction in which operators of equal precedence are evaluated. The two common associativities are:

• Left to Right (Left-Associative): Operators with left associativity are evaluated from left to right. For example, in the expression a + b + c , the addition operators have left associativity, so the expression is equivalent to (a + b) + c .
• Right to Left (Right-Associative): Operators with right associativity are evaluated from right to left. For example, in the expression a = b = c , the assignment operator = has right associativity, so the expression is equivalent to a = (b = c) .

Frequently Asked Questions (FAQs) related to Programming Operators :

Here are some frequently asked questions (FAQs) related to programming operators:

Q1: What are operators in programming?

A: Operators in programming are symbols that represent computations or actions to be performed on operands. They can manipulate data, perform calculations, and facilitate various operations in a program.

Q2: How are operators categorized?

A: Operators are categorized based on their functionality. Common categories include arithmetic operators (for mathematical operations), assignment operators (for assigning values), comparison operators (for comparing values), logical operators (for logical operations), and bitwise operators (for manipulating individual bits).

Q3: What is the difference between unary and binary operators?

A: Unary operators operate on a single operand, while binary operators operate on two operands. For example, the unary minus -x negates the value of x , while the binary plus a + b adds the values of a and b .

Q4: Can operators be overloaded in programming languages?

A: Yes, some programming languages support operator overloading, allowing developers to define custom behaviors for operators when applied to user-defined types. This is commonly seen in languages like C++.

Q5: How do logical AND ( && ) and logical OR ( || ) operators work?

A: The logical AND ( && ) operator returns true if both of its operands are true. The logical OR ( || ) operator returns true if at least one of its operands is true. These operators are often used in conditional statements and expressions.

Q6: What is the purpose of the ternary operator ( ?: )?

A: The ternary operator is a shorthand for an if-else statement. It evaluates a condition and returns one of two values based on whether the condition is true or false. It is often used for concise conditional assignments.

Q7: How does the bitwise XOR operator ( ^ ) work?

A: The bitwise XOR ( ^ ) operator performs an exclusive OR operation on individual bits. It returns 1 for bits that are different and 0 for bits that are the same. This operator is commonly used in bit manipulation tasks.

Q8: What is the difference between = and == ?

A: The = operator is an assignment operator used to assign a value to a variable. The == operator is a comparison operator used to check if two values are equal. It is important not to confuse the two, as = is used for assignment, and == is used for comparison.

Q9: How do increment ( ++ ) and decrement ( -- ) operators work?

A: The increment ( ++ ) operator adds 1 to the value of a variable, while the decrement ( -- ) operator subtracts 1. These operators can be used as prefix ( ++x ) or postfix ( x++ ), affecting the order of the increment or decrement operation.

Q10: Are operators language-specific?

A: While many operators are common across programming languages, some languages may introduce unique operators or have variations in their behavior. However, the fundamental concepts of arithmetic, logical, and bitwise operations are prevalent across various languages.

Q11: What is the modulus operator ( % ) used for?

A: The modulus operator ( % ) returns the remainder when one number is divided by another. It is often used to check divisibility or to cycle through a sequence of values. For example, a % 2 can be used to determine if a is an even or odd number.

Q12: Can the same operator have different meanings in different programming languages?

A: Yes, the same symbol may represent different operators or operations in different programming languages. For example, the + operator is used for addition in most languages, but in some languages (like JavaScript), it is also used for string concatenation.

Q13: What is short-circuit evaluation in the context of logical operators?

A: Short-circuit evaluation is a behavior where the second operand of a logical AND ( && ) or logical OR ( || ) operator is not evaluated if the outcome can be determined by the value of the first operand alone. This can lead to more efficient code execution.

Q14: How are bitwise left shift ( << ) and right shift ( >> ) operators used?

A: The bitwise left shift ( << ) operator shifts the bits of a binary number to the left, effectively multiplying the number by 2. The bitwise right shift ( >> ) operator shifts the bits to the right, effectively dividing the number by 2.

Q15: Can you provide an example of operator precedence in programming?

A: Operator precedence determines the order in which operators are evaluated. For example, in the expression a + b * c , the multiplication ( * ) has higher precedence than addition ( + ), so b * c is evaluated first.

Q16: How does the ternary operator differ from an if-else statement?

A: The ternary operator ( ?: ) is a concise way to express a conditional statement with a single line of code. It returns one of two values based on a condition. An if-else statement provides a more extensive code block for handling multiple statements based on a condition.

Q17: Are there any operators specifically designed for working with arrays or collections?

A: Some programming languages provide specific operators or methods for working with arrays or collections. For example, in Python, the in operator is used to check if an element is present in a list.

Q18: How can bitwise operators be used for efficient memory management?

A: Bitwise operators are often used for efficient memory management by manipulating individual bits. For example, bitwise AND can be used to mask specific bits, and bitwise OR can be used to set particular bits.

Q19: Can operators be overloaded in all programming languages?

A: No, not all programming languages support operator overloading. While some languages like C++ allow developers to redefine the behavior of operators for user-defined types, others, like Java, do not permit operator overloading.

Q20: How do you handle operator precedence in complex expressions?

A: Parentheses are used to explicitly specify the order of operations in complex expressions, ensuring that certain operations are performed before others. For example, (a + b) * c ensures that addition is performed before multiplication.

In conclusion, operators in programming are essential tools that enable the manipulation, comparison, and logical operations on variables and values. They form the building blocks of expressions and play a fundamental role in controlling program flow, making decisions, and performing calculations. From arithmetic and comparison operators for numerical tasks to logical operators for decision-making, and bitwise operators for low-level bit manipulation, each type serves specific purposes in diverse programming scenarios.

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What is the difference between the GNU Makefile variable assignments =, ?=, := and +=?

Can anybody give a clear explanation of how variable assignment really works in Makefiles.

What is the difference between :

I have read the section in GNU Make's manual, but it still doesn't make sense to me.

6 Answers 6

Normal setting of a variable, but any other variables mentioned with the value field are recursively expanded with their value at the point at which the variable is used, not the one it had when it was declared

Immediate Set

Setting of a variable with simple expansion of the values inside - values within it are expanded at declaration time.

Recursively expanded variables

The value you specify is installed verbatim; if it contains references to other variables, these references are expanded whenever this variable is substituted (in the course of expanding some other string). When this happens, it is called recursive expansion .

The catch : foo will be expanded to the value of $(bar) each time foo is evaluated, possibly resulting in different values. Surely you cannot call it "lazy"! This can surprise you if executed on midnight:

Simply expanded variable

Variables defined with ‘:=’ or ‘::=’ are simply expanded variables.

Simply expanded variables are defined by lines using ‘:=’ or ‘::=’ [...]. Both forms are equivalent in GNU make; however only the ‘::=’ form is described by the POSIX standard [...] 2012.

The value of a simply expanded variable is scanned once and for all, expanding any references to other variables and functions, when the variable is defined.

Not much to add. It's evaluated immediately, including recursive expansion of, well, recursively expanded variables.

The catch : If VARIABLE refers to ANOTHER_VARIABLE :

and ANOTHER_VARIABLE is not defined before this assignment, ANOTHER_VARIABLE will expand to an empty value.

Assign if not set

is equivalent to

where $(origin FOO) equals to undefined only if the variable was not set at all.

The catch : if FOO was set to an empty string, either in makefiles, shell environment, or command line overrides, it will not be assigned bar .

Appending :

When the variable in question has not been defined before, ‘+=’ acts just like normal ‘=’: it defines a recursively-expanded variable. However, when there is a previous definition, exactly what ‘+=’ does depends on what flavor of variable you defined originally.

So, this will print foo bar :

but this will print foo :

The catch is that += behaves differently depending on what type of variable VAR was assigned before.

Multiline values

The syntax to assign multiline value to a variable is:

Assignment operator can be omitted, then it creates a recursively-expanded variable.

The last newline before endef is removed.

Bonus: the shell assignment operator ‘!=’

is the same as

Don't use it. $(shell) call is more readable, and the usage of both in a makefiles is highly discouraged. At least, $(shell) follows Joel's advice and makes wrong code look obviously wrong .

• Are ?= and = equivalent when defining macros that are intended to be overridden by environment variables, like CFLAGS / CPPFLAGS / LDFLAGS ? –  shadowtalker Commented Aug 17, 2021 at 13:55
• 1 @shadowtalker, no. Make variables default to environment variables, but = overrides any existing value. Also note that command-line override variables (that go after make on command line) override every single assignment in Makefile , except for overrides . –  Victor Sergienko Commented Aug 17, 2021 at 18:26
• Does this sound correct? = and := override environment variables, environment variables override =? , command-line "override variables" override both, and the override directive overrides all of the above. This interaction with environment variables and command-line override might be a very helpful clarification in your already-very-thorough answer. –  shadowtalker Commented Aug 17, 2021 at 18:35
• 1 This is accurate. Thank you. I thought that this is a bit outside of the scope of the question. On the other hand, there is no question "How do Makefile variables get their values?". Maybe it's worth asking the question. –  Victor Sergienko Commented Aug 17, 2021 at 18:54
• I took your suggestion: stackoverflow.com/a/68825174/2954547 –  shadowtalker Commented Aug 17, 2021 at 23:51

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