assignment in c language

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Assignment Operators in C

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

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

In addition, C has several augmented assignment operators.

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

Simple Assignment Operator (=)

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

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

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

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

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

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

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

Augmented Assignment Operators

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

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

Run the code and check its output −

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

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

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

Next: Execution Control Expressions , Previous: Arithmetic , Up: Top   [ Contents ][ Index ]

7 Assignment Expressions

As a general concept in programming, an assignment is a construct that stores a new value into a place where values can be stored—for instance, in a variable. Such places are called lvalues (see Lvalues ) because they are locations that hold a value.

An assignment in C is an expression because it has a value; we call it an assignment expression . A simple assignment looks like

We say it assigns the value of the expression value-to-store to the location lvalue , or that it stores value-to-store there. You can think of the “l” in “lvalue” as standing for “left,” since that’s what you put on the left side of the assignment operator.

However, that’s not the only way to use an lvalue, and not all lvalues can be assigned to. To use the lvalue in the left side of an assignment, it has to be modifiable . In C, that means it was not declared with the type qualifier const (see const ).

The value of the assignment expression is that of lvalue after the new value is stored in it. This means you can use an assignment inside other expressions. Assignment operators are right-associative so that

is equivalent to

This is the only useful way for them to associate; the other way,

would be invalid since an assignment expression such as x = y is not valid as an lvalue.

Warning: Write parentheses around an assignment if you nest it inside another expression, unless that is a conditional expression, or comma-separated series, or another assignment.

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C Assignment Operators

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

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

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

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

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

• Assignment Operators

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cppreference.com

Assignment operators.

Assignment and compound assignment operators are binary operators that modify the variable to their left using the value to their right.

[ edit ] Simple assignment

The simple assignment operator expressions have the form

Assignment performs implicit conversion from the value of rhs to the type of lhs and then replaces the value in the object designated by lhs with the converted value of rhs .

Assignment also returns the same value as what was stored in lhs (so that expressions such as a = b = c are possible). The value category of the assignment operator is non-lvalue (so that expressions such as ( a = b ) = c are invalid).

rhs and lhs must satisfy one of the following:

• both lhs and rhs have compatible struct or union type, or..
• rhs must be implicitly convertible to lhs , which implies
• both lhs and rhs have arithmetic types , in which case lhs may be volatile -qualified or atomic (since C11)
• both lhs and rhs have pointer to compatible (ignoring qualifiers) types, or one of the pointers is a pointer to void, and the conversion would not add qualifiers to the pointed-to type. lhs may be volatile or restrict (since C99) -qualified or atomic (since C11) .
• lhs is a (possibly qualified or atomic (since C11) ) pointer and rhs is a null pointer constant such as NULL or a nullptr_t value (since C23)

[ edit ] Notes

If rhs and lhs overlap in memory (e.g. they are members of the same union), the behavior is undefined unless the overlap is exact and the types are compatible .

Although arrays are not assignable, an array wrapped in a struct is assignable to another object of the same (or compatible) struct type.

The side effect of updating lhs is sequenced after the value computations, but not the side effects of lhs and rhs themselves and the evaluations of the operands are, as usual, unsequenced relative to each other (so the expressions such as i = ++ i ; are undefined)

Assignment strips extra range and precision from floating-point expressions (see FLT_EVAL_METHOD ).

In C++, assignment operators are lvalue expressions, not so in C.

[ edit ] Compound assignment

The compound assignment operator expressions have the form

The expression lhs @= rhs is exactly the same as lhs = lhs @ ( rhs ) , except that lhs is evaluated only once.

[ edit ] References

• C17 standard (ISO/IEC 9899:2018):
• 6.5.16 Assignment operators (p: 72-73)
• C11 standard (ISO/IEC 9899:2011):
• 6.5.16 Assignment operators (p: 101-104)
• C99 standard (ISO/IEC 9899:1999):
• 6.5.16 Assignment operators (p: 91-93)
• C89/C90 standard (ISO/IEC 9899:1990):
• 3.3.16 Assignment operators

[ edit ] See Also

Operator precedence

[ edit ] See also

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02 beginner, 03 intermediate, 04 advanced, 05 training programs, c programming assignment operators, free c programming online course with certificate, what is an assignment operator in c, types of assignment operators in c.

1. Simple Assignment Operator (=)

Example of simple assignment operator.

2. Compound Assignment Operators

Example of Augmented Arithmetic and Assignment Operators

Example of Augmented Bitwise and Assignment Operators

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

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Assignment Operators in C

Assignment Operators in C Example

Home » Learn C Programming from Scratch » C Assignment Operators

C Assignment Operators

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

Introduction to the C assignment operators

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

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

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

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

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

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

The expression:

is equivalent to the following expression:

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

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

Assignment and shorthand assignment operator in C

Quick links.

• Shorthand assignment

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

For example consider the below assignment table.

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

Shorthand assignment operator

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

For example, consider following C statements.

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

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

Assignment Operators In C [ Full Information With Examples ]

Assignment Operators In C

Assignment operators is a binary operator which is used to assign values in a variable , with its right and left sides being a one-one operand. The operand on the left side is variable in which the value is assigned and the right side operands can contain any of the constant, variable, and expression.

The Assignment operator is a lower priority operator. its priority has much lower than the rest of the other operators. Its priority is more than just the comma operator. The priority of all other operators is more than the assignment operator.

We can assign the same value to multiple variables simultaneously by the assignment operator.

x = y = z = 100

Here x, y, and z are initialized to 100.

In C language, the assignment operator can be divided into two categories.

• Simple assignment operator
• Compound assignment operators

1. Simple Assignment Operator In C

This operator is used to assign left-side values ​​to the right-side operands, simple assignment operators are represented by (=).

2. Compound Assignment Operators In C

Compound Assignment Operators use the old value of a variable to calculate its new value and reassign the value obtained from the calculation to the same variable.

Examples of compound assignment operators are: (Example: + =, – =, * =, / =,% =, & =, ^ =)

Look at these two statements:

Here in this example, adding 5 to the x variable in the second statement is again being assigned to the x variable.

Compound Assignment Operators provide us with the C language to perform such operation even more effecient and in less time.

Syntax of Compound Assignment Operators

Here op can be any arithmetic operators (+, -, *, /,%).

The above statement is equivalent to the following depending on the function:

Let us now know about some important compound assignment operators one by one.

“+ =” -: This operator adds the right operand to the left operand and assigns the output to the left operand.

“- =” -: This operator subtracts the right operand from the left operand and returns the result to the left operand.

“* =” -: This operator multiplies the right operand with the left operand and assigns the result to the left operand.

“/ =” -: This operator splits the left operand with the right operand and assigns the result to the left operand.

“% =” -: This operator takes the modulus using two operands and assigns the result to the left operand.

There are many other assignment operators such as left shift and (<< =) operator, right shift and operator (>> =), bitwise and assignment operator (& =), bitwise OR assignment operator (^ =)

List of Assignment Operators In C

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Assignment operator in c.

Last Updated on June 23, 2023 by Prepbytes

This type of operator is employed for transforming and assigning values to variables within an operation. In an assignment operation, the right side represents a value, while the left side corresponds to a variable. It is essential that the value on the right side has the same data type as the variable on the left side. If this requirement is not fulfilled, the compiler will issue an error.

What is Assignment Operator in C language?

In C, the assignment operator serves the purpose of assigning a value to a variable. It is denoted by the equals sign (=) and plays a vital role in storing data within variables for further utilization in code. When using the assignment operator, the value present on the right-hand side is assigned to the variable on the left-hand side. This fundamental operation allows developers to store and manipulate data effectively throughout their programs.

Example of Assignment Operator in C

For example, consider the following line of code:

Types of Assignment Operators in C

Here is a list of the assignment operators that you can find in the C language:

Simple assignment operator (=): This is the basic assignment operator, which assigns the value on the right-hand side to the variable on the left-hand side.

Addition assignment operator (+=): This operator adds the value on the right-hand side to the variable on the left-hand side and assigns the result back to the variable.

x += 3; // Equivalent to x = x + 3; (adds 3 to the current value of "x" and assigns the result back to "x")

Subtraction assignment operator (-=): This operator subtracts the value on the right-hand side from the variable on the left-hand side and assigns the result back to the variable.

x -= 4; // Equivalent to x = x – 4; (subtracts 4 from the current value of "x" and assigns the result back to "x")

* Multiplication assignment operator ( =):** This operator multiplies the value on the right-hand side with the variable on the left-hand side and assigns the result back to the variable.

x = 2; // Equivalent to x = x 2; (multiplies the current value of "x" by 2 and assigns the result back to "x")

Division assignment operator (/=): This operator divides the variable on the left-hand side by the value on the right-hand side and assigns the result back to the variable.

x /= 2; // Equivalent to x = x / 2; (divides the current value of "x" by 2 and assigns the result back to "x")

Bitwise AND assignment (&=): The bitwise AND assignment operator "&=" performs a bitwise AND operation between the value on the left-hand side and the value on the right-hand side. It then assigns the result back to the left-hand side variable.

x &= 3; // Binary: 0011 // After bitwise AND assignment: x = 1 (Binary: 0001)

Bitwise OR assignment (|=): The bitwise OR assignment operator "|=" performs a bitwise OR operation between the value on the left-hand side and the value on the right-hand side. It then assigns the result back to the left-hand side variable.

x |= 3; // Binary: 0011 // After bitwise OR assignment: x = 7 (Binary: 0111)

Bitwise XOR assignment (^=): The bitwise XOR assignment operator "^=" performs a bitwise XOR operation between the value on the left-hand side and the value on the right-hand side. It then assigns the result back to the left-hand side variable.

x ^= 3; // Binary: 0011 // After bitwise XOR assignment: x = 6 (Binary: 0110)

Left shift assignment (<<=): The left shift assignment operator "<<=" shifts the bits of the value on the left-hand side to the left by the number of positions specified by the value on the right-hand side. It then assigns the result back to the left-hand side variable.

x <<= 2; // Binary: 010100 (Shifted left by 2 positions) // After left shift assignment: x = 20 (Binary: 10100)

Right shift assignment (>>=): The right shift assignment operator ">>=" shifts the bits of the value on the left-hand side to the right by the number of positions specified by the value on the right-hand side. It then assigns the result back to the left-hand side variable.

x >>= 2; // Binary: 101 (Shifted right by 2 positions) // After right shift assignment: x = 5 (Binary: 101)

Conclusion The assignment operator in C, denoted by the equals sign (=), is used to assign a value to a variable. It is a fundamental operation that allows programmers to store data in variables for further use in their code. In addition to the simple assignment operator, C provides compound assignment operators that combine arithmetic or bitwise operations with assignment, allowing for concise and efficient code.

FAQs related to Assignment Operator in C

Q1. Can I assign a value of one data type to a variable of another data type? In most cases, assigning a value of one data type to a variable of another data type will result in a warning or error from the compiler. It is generally recommended to assign values of compatible data types to variables.

Q2. What is the difference between the assignment operator (=) and the comparison operator (==)? The assignment operator (=) is used to assign a value to a variable, while the comparison operator (==) is used to check if two values are equal. It is important not to confuse these two operators.

Q3. Can I use multiple assignment operators in a single statement? No, it is not possible to use multiple assignment operators in a single statement. Each assignment operator should be used separately for assigning values to different variables.

Q4. Are there any limitations on the right-hand side value of the assignment operator? The right-hand side value of the assignment operator should be compatible with the data type of the left-hand side variable. If the data types are not compatible, it may lead to unexpected behavior or compiler errors.

Q5. Can I assign the result of an expression to a variable using the assignment operator? Yes, it is possible to assign the result of an expression to a variable using the assignment operator. For example, x = y + z; assigns the sum of y and z to the variable x.

Q6. What happens if I assign a value to an uninitialized variable? Assigning a value to an uninitialized variable will initialize it with the assigned value. However, it is considered good practice to explicitly initialize variables before using them to avoid potential bugs or unintended behavior.

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An operator is a symbol that operates on a value or a variable. For example: + is an operator to perform addition.

C has a wide range of operators to perform various operations.

C Arithmetic Operators

An arithmetic operator performs mathematical operations such as addition, subtraction, multiplication, division etc on numerical values (constants and variables).

Example 1: Arithmetic Operators

The operators + , - and * computes addition, subtraction, and multiplication respectively as you might have expected.

In normal calculation, 9/4 = 2.25 . However, the output is 2 in the program.

It is because both the variables a and b are integers. Hence, the output is also an integer. The compiler neglects the term after the decimal point and shows answer 2 instead of 2.25 .

The modulo operator % computes the remainder. When a=9 is divided by b=4 , the remainder is 1 . The % operator can only be used with integers.

Suppose a = 5.0 , b = 2.0 , c = 5 and d = 2 . Then in C programming,

C Increment and Decrement Operators

C programming has two operators increment ++ and decrement -- to change the value of an operand (constant or variable) by 1.

Increment ++ increases the value by 1 whereas decrement -- decreases the value by 1. These two operators are unary operators, meaning they only operate on a single operand.

Example 2: Increment and Decrement Operators

Here, the operators ++ and -- are used as prefixes. These two operators can also be used as postfixes like a++ and a-- . Visit this page to learn more about how increment and decrement operators work when used as postfix .

C Assignment Operators

An assignment operator is used for assigning a value to a variable. The most common assignment operator is =

Example 3: Assignment Operators

C relational operators.

A relational operator checks the relationship between two operands. If the relation is true, it returns 1; if the relation is false, it returns value 0.

Relational operators are used in decision making and loops .

Example 4: Relational Operators

C logical operators.

An expression containing logical operator returns either 0 or 1 depending upon whether expression results true or false. Logical operators are commonly used in decision making in C programming .

Example 5: Logical Operators

Explanation of logical operator program

• (a == b) && (c > 5) evaluates to 1 because both operands (a == b) and (c > b) is 1 (true).
• (a == b) && (c < b) evaluates to 0 because operand (c < b) is 0 (false).
• (a == b) || (c < b) evaluates to 1 because (a = b) is 1 (true).
• (a != b) || (c < b) evaluates to 0 because both operand (a != b) and (c < b) are 0 (false).
• !(a != b) evaluates to 1 because operand (a != b) is 0 (false). Hence, !(a != b) is 1 (true).
• !(a == b) evaluates to 0 because (a == b) is 1 (true). Hence, !(a == b) is 0 (false).

During computation, mathematical operations like: addition, subtraction, multiplication, division, etc are converted to bit-level which makes processing faster and saves power.

Bitwise operators are used in C programming to perform bit-level operations.

Visit bitwise operator in C to learn more.

Other Operators

Comma operator.

Comma operators are used to link related expressions together. For example:

The sizeof operator

The sizeof is a unary operator that returns the size of data (constants, variables, array, structure, etc).

Example 6: sizeof Operator

Other operators such as ternary operator ?: , reference operator & , dereference operator * and member selection operator  ->  will be discussed in later tutorials.

Table of Contents

• Arithmetic Operators
• Increment and Decrement Operators
• Assignment Operators
• Relational Operators
• Logical Operators
• sizeof Operator

Video: Arithmetic Operators in C

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Operators are used to perform operations on variables and values.

In the example below, we use the + operator to add together two values:

Although the + operator is often used to add together two values, like in the example above, it can also be used to add together a variable and a value, or a variable and another variable:

C divides the operators into the following groups:

• Arithmetic operators
• Assignment operators
• Comparison operators
• Logical operators
• Bitwise operators

Arithmetic Operators

Arithmetic operators are used to perform common mathematical operations.

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:

Comparison Operators

Comparison operators are used to compare two values (or variables). This is important in programming, because it helps us to find answers and make decisions.

The return value of a comparison is either 1 or 0 , which means true ( 1 ) or false ( 0 ). These values are known as Boolean values , and you will learn more about them in the Booleans and If..Else chapter.

Comparison operators are used to compare two values.

Note: The return value of a comparison is either true ( 1 ) or false ( 0 ).

In the following example, we use the greater than operator ( > ) to find out if 5 is greater than 3:

A list of all comparison operators:

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You can also test for true or false values with logical operators.

Logical operators are used to determine the logic between variables or values, by combining multiple conditions:

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C array declaration and assignment?

I've asked a similar question on structs here but I'm trying to figure out how C handles things like assigning variables and why it isn't allowed to assign them to eachother if they are functionally the same.

Lets say I have two arrays:

Why won't x = y compile? If they are both the same "signature" like that, then shouldn't you be able to assign them back and forth?

Can I declare these in a way that would allow me to do that in C? It makes sense to me that you would be able to, but maybe there is a way that this can be done? Typedefs for structs seemed to be the solution, would it be the same for array declaration and assignment?

I appreciate your guys help, I'm new to Stackoverflow but it has been a really good resource for me so far!

• variable-assignment

7 Answers 7

Simply put, arrays are not assignable. They are a "non-modifiable lvalue". This of course begs the question: why? Please refer to this question for more information:

Why does C++ support memberwise assignment of arrays within structs, but not generally?

Arrays are not pointers. x here does refer to an array, though in many circumstances this "decays" (is implicitly converted) to a pointer to its first element. Likewise, y too is the name of an array, not a pointer.

You can do array assignment within structs:

But you can't do it directly with arrays. Use memcpy .

• That code still doesn't do what he was wanting it to do though, does it? Perhaps I'm wrong, but I got the impression he was hoping to copy the contents of the y array into x. –  T.E.D. Commented Apr 13, 2009 at 18:18
• True. Fortunately, lots of other replies have indicated memcpy() is the correct choice. I'll add it in... –  user82238 Commented Apr 13, 2009 at 18:21
• 6 "The name of an array is actually the address of the first element of that array. \ The example code you provide here is attempting to assign to something which is not an l-value.": for the sake of posterity I thought I'd note that both of these sentences from the most highly voted answer are wrong. First, the name of an array most definitely is not a pointer (e.g. think sizeof()), it simply decays to a pointer in many cases. Second, the array name is an lvalue, just not a modifiable lvalue. –  Alexandros Gezerlis Commented Oct 31, 2011 at 23:32
• 3 I'm high-jacking this answer. It's top-voted and accepted, yet contained incorrect information and the user is long-gone. Hopefully this clears things up. –  GManNickG Commented Oct 5, 2016 at 6:16

This compiles and y will be the same as x .

• 4 y will be a pointer equivalent to &x[0] , due to array-to-pointer conversion, but it won't be "the same" as x is an array, not a pointer. –  GManNickG Commented Oct 5, 2016 at 6:05

Some messages here say that the name of an array yields the address of its first element. It's not always true:

In order to assign arrays you will have to assign the values inside the array.

ie. x=y is equivalent to

• thats why I am giving the equivalent! –  aJ. Commented Apr 13, 2009 at 16:55
• it gives the impression that x=y is a valid statement –  Naveen Commented Apr 13, 2009 at 16:57
• Actually in the OP its already mentioned that x=y doesn't compile. –  aJ. Commented Apr 13, 2009 at 16:58
• x=y being impossible for arrays is the entire context for this question, Naveen. –  Chuck Commented Apr 13, 2009 at 17:02

In an attempt to complement Blank's answer, I devised the following program:

When executed, the following is output:

The point is to illustrate how the copy of structures' values occurs.

When saying "int x[10]" is saying, "reserve some room for 10 integers and pass me a pointer to the location". So for the copy to make sense you'd need to operate on the memory pointed by, rather than 'the name of the memory location'.

So for copying here you'd use a for loop or memcpy().

I've used C compilers where that would compile just fine...and when run the code would make x point to y's array.

You see, in C the name of an array is a pointer that points to the start of the array. In fact, arrays and pointers are essentially interchangable. You can take any pointer and index it like an array.

Back when C was being developed in the early 70's, it was meant for relatively small programs that were barely above assembly language in abstraction. In that environment, it was damn handy to be able to easily go back and forth between array indexing and pointer math. Copying whole arrays of data, on the other hand, was a very expensive thing do do, and hardly something to be encouraged or abstracted away from the user.

Yes, in these modern times it would make way more sense to have the name of the array be shorthand for "the whole array", rather than for "a ponter to the front of the array". However, C wasn't designed in these modern times. If you want a language that was, try Ada. x := y there does exactly what you would expect; it copies one array's contents to the other.

• Friendly random ping. :) As you undoubtedly (now) know, the name of an array is not a pointer. –  GManNickG Commented Oct 5, 2016 at 6:05

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Pointers are one of the core components of the C programming language. A pointer can be used to store the memory address of other variables, functions, or even other pointers. The use of pointers allows low-level memory access, dynamic memory allocation, and many other functionality in C.

In this article, we will discuss C pointers in detail, their types, uses, advantages, and disadvantages with examples.

What is a Pointer in C?

A pointer is defined as a derived data type that can store the address of other C variables or a memory location. We can access and manipulate the data stored in that memory location using pointers.

As the pointers in C store the memory addresses, their size is independent of the type of data they are pointing to. This size of pointers in C only depends on the system architecture.

Syntax of C Pointers

The syntax of pointers is similar to the variable declaration in C, but we use the ( * ) dereferencing operator in the pointer declaration.

• ptr is the name of the pointer.
• datatype is the type of data it is pointing to.

The above syntax is used to define a pointer to a variable. We can also define pointers to functions, structures, etc.

How to Use Pointers?

The use of pointers in C can be divided into three steps:

• Pointer Declaration
• Pointer Initialization
• Pointer Dereferencing

1. Pointer Declaration

In pointer declaration, we only declare the pointer but do not initialize it. To declare a pointer, we use the ( * ) dereference operator before its name.

The pointer declared here will point to some random memory address as it is not initialized. Such pointers are called wild pointers.

2. Pointer Initialization

Pointer initialization is the process where we assign some initial value to the pointer variable. We generally use the ( &: ampersand ) addressof operator to get the memory address of a variable and then store it in the pointer variable.

We can also declare and initialize the pointer in a single step. This method is called pointer definition as the pointer is declared and initialized at the same time.

Note: It is recommended that the pointers should always be initialized to some value before starting using it. Otherwise, it may lead to number of errors.

3. Pointer Dereferencing

Dereferencing a pointer is the process of accessing the value stored in the memory address specified in the pointer. We use the same ( * ) dereferencing operator that we used in the pointer declaration.

Dereferencing a Pointer in C

C Pointer Example

Types of pointers in c.

Pointers in C can be classified into many different types based on the parameter on which we are defining their types. If we consider the type of variable stored in the memory location pointed by the pointer, then the pointers can be classified into the following types:

1. Integer Pointers

As the name suggests, these are the pointers that point to the integer values.

These pointers are pronounced as Pointer to Integer.

Similarly, a pointer can point to any primitive data type. It can point also point to derived data types such as arrays and user-defined data types such as structures.

2. Array Pointer

Pointers and Array are closely related to each other. Even the array name is the pointer to its first element. They are also known as Pointer to Arrays . We can create a pointer to an array using the given syntax.

Pointer to Arrays exhibits some interesting properties which we discussed later in this article.

3. Structure Pointer

The pointer pointing to the structure type is called Structure Pointer or Pointer to Structure. It can be declared in the same way as we declare the other primitive data types.

In C, structure pointers are used in data structures such as linked lists, trees, etc.

4. Function Pointers

Function pointers point to the functions. They are different from the rest of the pointers in the sense that instead of pointing to the data, they point to the code. Let’s consider a function prototype – int func (int, char) , the function pointer for this function will be

Note: The syntax of the function pointers changes according to the function prototype.

5. Double Pointers

In C language, we can define a pointer that stores the memory address of another pointer. Such pointers are called double-pointers or pointers-to-pointer . Instead of pointing to a data value, they point to another pointer.

Dereferencing Double Pointer

Note: In C, we can create multi-level pointers with any number of levels such as – ***ptr3, ****ptr4, ******ptr5 and so on.

6. NULL Pointer

The Null Pointers are those pointers that do not point to any memory location. They can be created by assigning a NULL value to the pointer. A pointer of any type can be assigned the NULL value.

It is said to be good practice to assign NULL to the pointers currently not in use.

7. Void Pointer

The Void pointers in C are the pointers of type void. It means that they do not have any associated data type. They are also called generic pointers as they can point to any type and can be typecasted to any type.

One of the main properties of void pointers is that they cannot be dereferenced.

8. Wild Pointers

The Wild Pointers are pointers that have not been initialized with something yet. These types of C-pointers can cause problems in our programs and can eventually cause them to crash. If values is updated using wild pointers, they could cause data abort or data corruption.

9. Constant Pointers

In constant pointers, the memory address stored inside the pointer is constant and cannot be modified once it is defined. It will always point to the same memory address.

10. Pointer to Constant

The pointers pointing to a constant value that cannot be modified are called pointers to a constant. Here we can only access the data pointed by the pointer, but cannot modify it. Although, we can change the address stored in the pointer to constant.

Other Types of Pointers in C:

There are also the following types of pointers available to use in C apart from those specified above:

• Far pointer : A far pointer is typically 32-bit that can access memory outside the current segment.
• Dangling pointer : A pointer pointing to a memory location that has been deleted (or freed) is called a dangling pointer.
• Huge pointer : A huge pointer is 32-bit long containing segment address and offset address.
• Complex pointer: Pointers with multiple levels of indirection.
• Near pointer : Near pointer is used to store 16-bit addresses means within the current segment on a 16-bit machine.
• Normalized pointer: It is a 32-bit pointer, which has as much of its value in the segment register as possible.
• File Pointer: The pointer to a FILE data type is called a stream pointer or a file pointer.

Size of Pointers in C

The size of the pointers in C is equal for every pointer type. The size of the pointer does not depend on the type it is pointing to. It only depends on the operating system and CPU architecture. The size of pointers in C is 

• 8 bytes for a 64-bit System
• 4 bytes for a 32-bit System

The reason for the same size is that the pointers store the memory addresses, no matter what type they are. As the space required to store the addresses of the different memory locations is the same, the memory required by one pointer type will be equal to the memory required by other pointer types.

How to find the size of pointers in C?

We can find the size of pointers using the sizeof operator as shown in the following program:

Example: C Program to find the size of different pointer types.

As we can see, no matter what the type of pointer it is, the size of each and every pointer is the same.

Now, one may wonder that if the size of all the pointers is the same, then why do we need to declare the pointer type in the declaration? The type declaration is needed in the pointer for dereferencing and pointer arithmetic purposes.

C Pointer Arithmetic

The Pointer Arithmetic refers to the legal or valid arithmetic operations that can be performed on a pointer. It is slightly different from the ones that we generally use for mathematical calculations as only a limited set of operations can be performed on pointers. These operations include:

• Increment in a Pointer
• Decrement in a Pointer
• Addition of integer to a pointer
• Subtraction of integer to a pointer
• Subtracting two pointers of the same type
• Comparison of pointers of the same type.
• Assignment of pointers of the same type.

C Pointers and Arrays

In C programming language, pointers and arrays are closely related. An array name acts like a pointer constant. The value of this pointer constant is the address of the first element. For example, if we have an array named val then val and &val[0] can be used interchangeably.

If we assign this value to a non-constant pointer of the same type, then we can access the elements of the array using this pointer.

Example 1: Accessing Array Elements using Pointer with Array Subscript

Not only that, as the array elements are stored continuously, we can pointer arithmetic operations such as increment, decrement, addition, and subtraction of integers on pointer to move between array elements.

Example 2: Accessing Array Elements using Pointer Arithmetic

This concept is not limited to the one-dimensional array, we can refer to a multidimensional array element as well using pointers.

To know more about pointers to an array, refer to this article – Pointer to an Array

Uses of Pointers in C

The C pointer is a very powerful tool that is widely used in C programming to perform various useful operations. It is used to achieve the following functionalities in C:

• Pass Arguments by Reference
• Accessing Array Elements
• Return Multiple Values from Function
• Dynamic Memory Allocation
• Implementing Data Structures
• In System-Level Programming where memory addresses are useful.
• In locating the exact value at some memory location.
• To avoid compiler confusion for the same variable name.
• To use in Control Tables.

Advantages of Pointers

Following are the major advantages of pointers in C:

• Pointers are used for dynamic memory allocation and deallocation.
• An Array or a structure can be accessed efficiently with pointers
• Pointers are useful for accessing memory locations.
• Pointers are used to form complex data structures such as linked lists, graphs, trees, etc.
• Pointers reduce the length of the program and its execution time as well.

Disadvantages of Pointers

Pointers are vulnerable to errors and have following disadvantages:

• Memory corruption can occur if an incorrect value is provided to pointers.
• Pointers are a little bit complex to understand.
• Pointers are majorly responsible for memory leaks in C .
• Pointers are comparatively slower than variables in C.
• Uninitialized pointers might cause a segmentation fault.

In conclusion, pointers in C are very capable tools and provide C language with its distinguishing features, such as low-level memory access, referencing, etc. But as powerful as they are, they should be used with responsibility as they are one of the most vulnerable parts of the language.

FAQs on Pointers in C

Q1. define pointers..

Pointers are the variables that can store the memory address of another variable.

Q2. What is the difference between a constant pointer and a pointer to a constant?

A constant pointer points to the fixed memory location, i.e. we cannot change the memory address stored inside the constant pointer. On the other hand, the pointer to a constant point to the memory with a constant value.

Q3. What is pointer to pointer?

A pointer to a pointer (also known as a double pointer) stores the address of another pointer.

Q4. Does pointer size depends on its type?

No, the pointer size does not depend upon its type. It only depends on the operating system and CPU architecture.

Q5. What are the differences between an array and a pointer?

The following table list the differences between an array and a pointer : Pointer Array A pointer is a derived data type that can store the address of other variables. An array is a homogeneous collection of items of any type such as int, char, etc. Pointers are allocated at run time. Arrays are allocated at runtime. The pointer is a single variable. An array is a collection of variables of the same type. Dynamic in Nature Static in Nature.

Q6. Why do we need to specify the type in the pointer declaration?

Type specification in pointer declaration helps the compiler in dereferencing and pointer arithmetic operations.

• Quiz on Pointer Basics
• Quiz on Advanced Pointer

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