c assignment order of evaluation

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C operator precedence.

The following table lists the precedence and associativity of C operators. Operators are listed top to bottom, in descending precedence.

↑ The operand of prefix ++ and -- can't be a type cast. This rule grammatically forbids some expressions that would be semantically invalid anyway. Some compilers ignore this rule and detect the invalidity semantically.
↑ The operand of sizeof can't be a type cast: the expression sizeof ( int ) * p is unambiguously interpreted as ( sizeof ( int ) ) * p , but not sizeof ( ( int ) * p ) .
↑ The expression in the middle of the conditional operator (between ? and : ) is parsed as if parenthesized: its precedence relative to ?: is ignored.
↑ Assignment operators' left operands must be unary (level-2 non-cast) expressions. This rule grammatically forbids some expressions that would be semantically invalid anyway. Many compilers ignore this rule and detect the invalidity semantically. For example, e = a < d ? a ++ : a = d is an expression that cannot be parsed because of this rule. However, many compilers ignore this rule and parse it as e = ( ( ( a < d ) ? ( a ++ ) : a ) = d ) , and then give an error because it is semantically invalid.

When parsing an expression, an operator which is listed on some row will be bound tighter (as if by parentheses) to its arguments than any operator that is listed on a row further below it. For example, the expression * p ++ is parsed as * ( p ++ ) , and not as ( * p ) ++ .

Operators that are in the same cell (there may be several rows of operators listed in a cell) are evaluated with the same precedence, in the given direction. For example, the expression a = b = c is parsed as a = ( b = c ) , and not as ( a = b ) = c because of right-to-left associativity.

[ edit ] Notes

Precedence and associativity are independent from order of evaluation .

The standard itself doesn't specify precedence levels. They are derived from the grammar.

In C++, the conditional operator has the same precedence as assignment operators, and prefix ++ and -- and assignment operators don't have the restrictions about their operands.

Associativity specification is redundant for unary operators and is only shown for completeness: unary prefix operators always associate right-to-left ( sizeof ++* p is sizeof ( ++ ( * p ) ) ) and unary postfix operators always associate left-to-right ( a [ 1 ] [ 2 ] ++ is ( ( a [ 1 ] ) [ 2 ] ) ++ ). Note that the associativity is meaningful for member access operators, even though they are grouped with unary postfix operators: a. b ++ is parsed ( a. b ) ++ and not a. ( b ++ ) .

[ edit ] References

C17 standard (ISO/IEC 9899:2018):
A.2.1 Expressions
C11 standard (ISO/IEC 9899:2011):
C99 standard (ISO/IEC 9899:1999):
C89/C90 standard (ISO/IEC 9899:1990):
A.1.2.1 Expressions

[ edit ] See also

Order of evaluation of operator arguments at run time.

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Operator precedence and associativity in c.

The concept of operator precedence and associativity in C helps in determining which operators will be given priority when there are multiple operators in the expression. It is very common to have multiple operators in C language and the compiler first evaluates the operater with higher precedence. It helps to maintain the ambiguity of the expression and helps us in avoiding unnecessary use of parenthesis.

In this article, we will discuss operator precedence, operator associativity, and precedence table according to which the priority of the operators in expression is decided in C language.

Operator Precedence and Associativity Table

The following tables list the C operator precedence from highest to lowest and the associativity for each of the operators:

Easy Trick to Remember the Operators Associtivity and Precedence: PUMA’S REBL TAC where, P = Postfix, U = Unary, M = Multiplicative, A = Additive, S = Shift, R = Relational, E = Equality, B = Bitwise, L = Logical, T = Ternary, A = Assignment and C = Comma

Operator Precedence in C

Operator precedence determines which operation is performed first in an expression with more than one operator with different precedence.

Example of Operator Precedence

Let’s try to evaluate the following expression,

The expression contains two operators, + (plus) , and * (multiply). According to the given table, the * has higher precedence than + so, the first evaluation will be

After evaluating the higher precedence operator, the expression is

Now, the + operator will be evaluated.

We can verify this using the following C program

As we can see, the expression is evaluated as, 10 + (20 * 30) but not as (10 + 20) * 30 due to * operator having higher precedence.

Operator Associativity

Operator associativity is used when two operators of the same precedence appear in an expression. Associativity can be either from Left to Right or Right to Left.

Example of Operator Associativity

Let’s evaluate the following expression,

Both / (division) and % (Modulus) operators have the same precedence, so the order of evaluation will be decided by associativity.

According to the given table, the associativity of the multiplicative operators is from Left to Right. So,

After evaluation, the expression will be

Now, the % operator will be evaluated.

We can verify the above using the following C program:

Operators Precedence and Associativity are two characteristics of operators that determine the evaluation order of sub-expressions.

Example of Operator Precedence and Associativity

In general, the concept of precedence and associativity is applied together in expressions. So let’s consider an expression where we have operators with various precedence and associativity

Here, we have four operators, in which the / and * operators have the same precedence but have higher precedence than the + and – operators. So, according to the Left-to-Right associativity of / and * , / will be evaluated first.

After that, * will be evaluated,

Now, between + and – , + will be evaluated due to Left-to-Right associativity.

At last, – will be evaluated.

Again, we can verify this using the following C program.

100 + 200 / 10 – 3 * 10 = 90

Important Points

There are a few important points and cases that we need to remember for operator associativity and precedence which are as follows:

1. Associativity is only used when there are two or more operators of the same precedence.

The point to note is associativity doesn’t define the order in which operands of a single operator are evaluated. For example, consider the following program, associativity of the + operator is left to right, but it doesn’t mean f1() is always called before f2(). The output of the following program is in-fact compiler-dependent.

See this for details.

2. We can use parenthesis to change the order of evaluation

Parenthesis ( ) got the highest priority among all the C operators. So, if we want to change the order of evaluation in an expression, we can enclose that particular operator in ( ) parenthesis along with its operands.

Consider the given expression

But if we enclose 100 + 200 in parenthesis, then the result will be different.

As the + operator will be evaluated before / operator.

2. All operators with the same precedence have the same associativity.

This is necessary, otherwise, there won’t be any way for the compiler to decide the evaluation order of expressions that have two operators of the same precedence and different associativity. For example + and – have the same associativity.

3. Precedence and associativity of postfix ++ and prefix ++ are different.

The precedence of postfix ++ is more than prefix ++, their associativity is also different. The associativity of postfix ++ is left to right and the associativity of prefix ++ is right to left. See this for examples.

4. Comma has the least precedence among all operators and should be used carefully.

For example, consider the following program, the output is 1.

See this , this for more details.

5. There is no chaining of comparison operators in C

In Python, an expression like “c > b > a” is treated as “c > b and b > a”, but this type of chaining doesn’t happen in C. For example, consider the following program. The output of the following program is “FALSE”.

It is necessary to know the precedence and associativity for the efficient usage of operators. It allows us to write clean expressions by avoiding the use of unnecessary parenthesis. Also, it is the same for all the C compilers so it also allows us to understand the expressions in the code written by other programmers.

Also, when confused about or want to change the order of evaluation, we can always rely on parenthesis ( ) . The advantage of brackets is that the reader doesn’t have to see the table to find out the order.

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Pointer vs Array in C Most of the time, pointer and array accesses can be treated as acting the same, the major exceptions being: 1. the sizeof operator sizeof(array) returns the amount of memory used by all elements in the array sizeof(pointer) only returns the amount of memory used by the pointer variable itself 2. the 1 min read
Dangling, Void , Null and Wild Pointers in C In C programming pointers are used to manipulate memory addresses, to store the address of some variable or memory location. But certain situations and characteristics related to pointers become challenging in terms of memory safety and program behavior these include Dangling (when pointing to deall 6 min read
Near, Far and Huge Pointers in C In older times, the intel processors had 16-bit registers but the address bus was 20-bits wide. Due to this, the registers were not able to hold the entire address at once. As a solution, the memory was divided into segments of 64 kB size, and the near pointers, far pointers, and huge pointers were 4 min read
restrict keyword in C In the C programming language (after the C99 standard), a new keyword is introduced known as restrict. restrict keyword is mainly used in pointer declarations as a type qualifier for pointers.It doesn't add any new functionality. It is only a way for the programmer to inform about an optimization th 2 min read

C User-Defined Data Types

C Structures The structure in C is a user-defined data type that can be used to group items of possibly different types into a single type. The struct keyword is used to define the structure in the C programming language. The items in the structure are called its member and they can be of any valid data type. Ad 10 min read
dot (.) Operator in C The C dot (.) operator is used for direct member selection via the name of variables of type struct and union. Also known as the direct member access operator, it is a binary operator that helps us to extract the value of members of the structures and unions. Syntax of Dot Operatorvariable_name.memb 2 min read
C typedef The typedef is a keyword that is used to provide existing data types with a new name. The C typedef keyword is used to redefine the name of already existing data types. When names of datatypes become difficult to use in programs, typedef is used with user-defined datatypes, which behave similarly to 4 min read
Structure Member Alignment, Padding and Data Packing In C, the structures are used as data packs. They don't provide any data encapsulation or data hiding features. In this article, we will discuss the property of structure padding in C along with data alignment and structure packing. Data Alignment in MemoryEvery data type in C will have alignment re 12 min read
Flexible Array Members in a structure in C Flexible Array Member(FAM) is a feature introduced in the C99 standard of the C programming language. For the structures in C programming language from C99 standard onwards, we can declare an array without a dimension and whose size is flexible in nature.Such an array inside the structure should pre 4 min read
C Unions The Union is a user-defined data type in C language that can contain elements of the different data types just like structure. But unlike structures, all the members in the C union are stored in the same memory location. Due to this, only one member can store data at the given instance. Syntax of Un 5 min read
Bit Fields in C In C, we can specify the size (in bits) of the structure and union members. The idea of bit-field is to use memory efficiently when we know that the value of a field or group of fields will never exceed a limit or is within a small range. C Bit fields are used when the storage of our program is limi 8 min read
Difference Between Structure and Union in C Structures in C is a user-defined data type available in C that allows to combining of data items of different kinds. Structures are used to represent a record. Defining a structure: To define a structure, you must use the struct statement. The struct statement defines a new data type, with more tha 4 min read
Anonymous Union and Structure in C In C11 standard of C, anonymous Unions and structures were added. Anonymous unions/structures are also known as unnamed unions/structures as they don't have names. Since there is no names, direct objects(or variables) of them are not created and we use them in nested structure or unions. Definition 2 min read
Enumeration (or enum) in C Enumeration (or enum) is a user defined data type in C. It is mainly used to assign names to integral constants, the names make a program easy to read and maintain. enum State {Working = 1, Failed = 0}; The keyword 'enum' is used to declare new enumeration types in C and C++. Enums in C allow you to 4 min read

C Storage Classes

Storage Classes in C C Storage Classes are used to describe the features of a variable/function. These features basically include the scope, visibility, and lifetime which help us to trace the existence of a particular variable during the runtime of a program. C language uses 4 storage classes, namely: Storage classes i 7 min read
extern Keyword in C extern keyword in C applies to C variables (data objects) and C functions. Basically, the extern keyword extends the visibility of the C variables and C functions. That's probably the reason why it was named extern. Though most people probably understand the difference between the "declaration" and 7 min read
Static Variables in C Static variables have the property of preserving their value even after they are out of their scope! Hence, a static variable preserves its previous value in its previous scope and is not initialized again in the new scope. Syntax: static data_type var_name = var_value;Static variables in C retain t 4 min read
Initialization of static variables in C In C, static variables can only be initialized using constant literals. For example, following program fails in compilation. [GFGTABS] C #include<stdio.h> int initializer(void) { return 50; } int main() { static int i = initializer(); printf(" value of i = %d", i); getchar(); return 1 min read
Static functions in C In C, functions are global by default. The “static” keyword before a function name makes it static. For example, the below function fun() is static. [GFGTABS] C static int fun(void) { printf("I am a static function "); } [/GFGTABS]Unlike global functions in C, access to static functions is 2 min read
Understanding "volatile" qualifier in C | Set 2 (Examples) The volatile keyword is intended to prevent the compiler from applying any optimizations on objects that can change in ways that cannot be determined by the compiler. Objects declared as volatile are omitted from optimization because their values can be changed by code outside the scope of current c 6 min read
Understanding "register" keyword in C Registers are faster than memory to access, so the variables which are most frequently used in a C program can be put in registers using the register keyword. The keyword register hints to the compiler that a given variable can be put in a register. It's the compiler's choice to put it in a register 3 min read

C Memory Management

Memory Layout of C Programs A typical memory representation of a C program consists of the following sections. Text segment (i.e. instructions)Initialized data segment Uninitialized data segment (bss)Heap Stack A typical memory layout of a running process 1. Text Segment: A text segment, also known as a code segment or simply 6 min read
Dynamic Memory Allocation in C using malloc(), calloc(), free() and realloc() Since C is a structured language, it has some fixed rules for programming. One of them includes changing the size of an array. An array is a collection of items stored at contiguous memory locations. As can be seen, the length (size) of the array above is 9. But what if there is a requirement to cha 9 min read
Difference Between malloc() and calloc() with Examples The functions malloc() and calloc() are library functions that allocate memory dynamically. Dynamic means the memory is allocated during runtime (execution of the program) from the heap segment. Initializationmalloc() allocates a memory block of given size (in bytes) and returns a pointer to the beg 3 min read
What is Memory Leak? How can we avoid? A memory leak occurs when programmers create a memory in a heap and forget to delete it. The consequence of the memory leak is that it reduces the performance of the computer by reducing the amount of available memory. Eventually, in the worst case, too much of the available memory may become alloca 3 min read
Dynamic Array in C Array in C is static in nature, so its size should be known at compile time and we can't change the size of the array after its declaration. Due to this, we may encounter situations where our array doesn't have enough space left for required elements or we allotted more than the required memory lead 9 min read
How to dynamically allocate a 2D array in C? Following are different ways to create a 2D array on the heap (or dynamically allocate a 2D array).In the following examples, we have considered 'r' as number of rows, 'c' as number of columns and we created a 2D array with r = 3, c = 4 and the following values 1 2 3 4 5 6 7 8 9 10 11 12 1) Using a 5 min read
Dynamically Growing Array in C Prerequisite: Dynamic Memory Allocation in C A Dynamically Growing Array is a type of dynamic array, which can automatically grow in size to store data. The C language only has static arrays whose size should be known at compile time and cannot be changed after declaration. This leads to problems li 7 min read

C Preprocessor

C Preprocessors Preprocessors are programs that process the source code before compilation. Several steps are involved between writing a program and executing a program in C. Let us have a look at these steps before we actually start learning about Preprocessors. You can see the intermediate steps in the above diag 10 min read
C Preprocessor Directives In almost every C program we come across, we see a few lines at the top of the program preceded by a hash (#) sign. They are called preprocessor directives and are preprocessed by the preprocessor before actual compilation begins. The end of these lines is identified by the newline character '\n', n 8 min read
How a Preprocessor works in C? Compiling a C program - Behind the Scene A Preprocessor is a system software (a computer program that is designed to run on computer's hardware and application programs). It performs preprocessing of the High Level Language(HLL). Preprocessing is the first step of the language processing system. Lan 3 min read
Header Files in C In C language, header files contain a set of predefined standard library functions. The .h is the extension of the header files in C and we request to use a header file in our program by including it with the C preprocessing directive "#include". C Header files offer the features like library functi 7 min read
What’s difference between header files "stdio.h" and "stdlib.h" ? These are two important header files used in C programming. While “<stdio.h>” is header file for Standard Input Output, “<stdlib.h>” is header file for Standard Library. One easy way to differentiate these two header files is that “<stdio.h>” contains declaration of printf() and sc 2 min read
How to write your own header file in C? As we all know that files with .h extension are called header files in C. These header files generally contain function declarations which we can be used in our main C program, like for e.g. there is need to include stdio.h in our C program to use function printf() in the program. So the question ar 4 min read
Macros and its types in C In C, a macro is a piece of code in a program that is replaced by the value of the macro. Macro is defined by #define directive. Whenever a macro name is encountered by the compiler, it replaces the name with the definition of the macro. Macro definitions need not be terminated by a semi-colon(;). E 6 min read
Interesting Facts about Macros and Preprocessors in C In a C program, all lines that start with # are processed by preprocessor which is a special program invoked by the compiler. by this we mean to say that the ‘#’ symbol is used to process the functionality prior than other statements in the program, that is, which means it processes some code before 6 min read
# and ## Operators in C Stringizing operator (#)The stringizing operator (#) is a preprocessor operator that causes the corresponding actual argument to be enclosed in double quotation marks. The # operator, which is generally called the stringize operator, turns the argument it precedes into a quoted string. It is also kn 2 min read
How to print a variable name in C? How to print and store a variable name in string variable? We strongly recommend you to minimize your browser and try this yourself first In C, there’s a # directive, also called ‘Stringizing Operator’, which does this magic. Basically # directive converts its argument in a string. #include <stdi 1 min read
Multiline macros in C In this article, we will discuss how to write a multi-line macro. We can write multi-line macro same like function, but each statement ends with "\". Let us see with example. Below is simple macro, which accepts input number from user, and prints whether entered number is even or odd. #include <s 3 min read
Variable length arguments for Macros Like functions, we can also pass variable length arguments to macros. For this we will use the following preprocessor identifiers.To support variable length arguments in macro, we must include ellipses (...) in macro definition. There is also "__VA_ARGS__" preprocessing identifier which takes care o 2 min read
Branch prediction macros in GCC One of the most used optimization techniques in the Linux kernel is " __builtin_expect". When working with conditional code (if-else statements), we often know which branch is true and which is not. If compiler knows this information in advance, it can generate most optimized code. Let us see macro 2 min read
typedef versus #define in C typedef: The typedef is used to give data type a new name. For example, // C program to demonstrate typedef #include <stdio.h> // After this line BYTE can be used // in place of unsigned char typedef unsigned char BYTE; int main() { BYTE b1, b2; b1 = 'c'; printf("%c ", b1); return 0; 3 min read
Difference between #define and const in C? #define is a preprocessor directive. Data defined by the #define macro definition are preprocessed, so that your entire code can use it. This can free up space and increase compilation times.const variables are considered variables, and not macro definitions. Long story short: CONSTs are handled by 2 min read
Basics of File Handling in C File handling in C is the process in which we create, open, read, write, and close operations on a file. C language provides different functions such as fopen(), fwrite(), fread(), fseek(), fprintf(), etc. to perform input, output, and many different C file operations in our program. Why do we need 15 min read
C fopen() function with Examples The fopen() method in C is a library function that is used to open a file to perform various operations which include reading, writing, etc. along with various modes. If the file exists then the fopen() function opens the particular file else a new file is created. SyntaxThe syntax of C fopen() is: 5 min read
EOF, getc() and feof() in C In C/C++, getc() returns the End of File (EOF) when the end of the file is reached. getc() also returns EOF when it fails. So, only comparing the value returned by getc() with EOF is not sufficient to check for the actual end of the file. To solve this problem, C provides feof() which returns a non- 3 min read
fgets() and gets() in C language For reading a string value with spaces, we can use either gets() or fgets() in C programming language. Here, we will see what is the difference between gets() and fgets(). fgets()The fgets() reads a line from the specified stream and stores it into the string pointed to by str. It stops when either 3 min read
fseek() vs rewind() in C fseek() and rewind() both functions are used to file positioning defined in <stdio.h> header file. In this article, we will discuss the differences in the usage and behavior of both functions. fseek() Function fseek() is used to set the file position indicator to a specified offset from the sp 3 min read
What is return type of getchar(), fgetc() and getc() ? In C, return type of getchar(), fgetc() and getc() is int (not char). So it is recommended to assign the returned values of these functions to an integer type variable. char ch; /* May cause problems */ while ((ch = getchar()) != EOF) { putchar(ch); } Here is a version that uses integer to compare t 1 min read
Read/Write Structure From/to a File in C For writing in the file, it is easy to write string or int to file using fprintf and putc, but you might have faced difficulty when writing contents of the struct. fwrite and fread make tasks easier when you want to write and read blocks of data. Writing Structure to a File using fwriteWe can use fw 3 min read
C Program to print contents of file In C, reading the contents of a file involves opening the file, reading its data, and then processing or displaying the data. Example Input: File containing “This is a test file.\nIt has multiple lines.” Output: This is a test file.It has multiple lines. Explanation: The program reads and displays t 7 min read
C program to delete a file The remove() function in C/C++ can be used to delete a file. The function returns 0 if the file is deleted successfully, Otherwise, it returns a non-zero value. The remove() is defined inside the <stdio.h> header file. Syntax of remove()remove("filename");ParametersThis function takes a string 2 min read
C Program to merge contents of two files into a third file Let the given two files be file1.txt and file2.txt. The following are steps to merge. 1) Open file1.txt and file2.txt in read mode. 2) Open file3.txt in write mode. 3) Run a loop to one by one copy characters of file1.txt to file3.txt. 4) Run a loop to one by one copy characters of file2.txt to file 2 min read
What is the difference between printf, sprintf and fprintf? printf: printf function is used to print character stream of data on stdout console. Syntax : printf(const char* str, ...); Example : C/C++ Code // simple print on stdout #include <stdio.h> int main() { printf("hello geeksquiz"); return 0; } Outputhello geeksquiz sprintf: String prin 2 min read
Difference between getc(), getchar(), getch() and getche() All of these functions read a character from input and return an integer value. The integer is returned to accommodate a special value used to indicate failure. The value EOF is generally used for this purpose. getc() It reads a single character from a given input stream and returns the correspondin 2 min read

Miscellaneous

time.h header file in C with Examples The time.h header file contains definitions of functions to get and manipulate date and time information. It describes three time-related data types. clock_t: clock_t represents the date as an integer which is a part of the calendar time. time_t: time_t represents the clock time as an integer which 4 min read
Input-output system calls in C | Create, Open, Close, Read, Write System calls are the calls that a program makes to the system kernel to provide the services to which the program does not have direct access. For example, providing access to input and output devices such as monitors and keyboards. We can use various functions provided in the C Programming language 10 min read
Signals in C language Prerequisite : Fork system call, Wait system call A signal is a software generated interrupt that is sent to a process by the OS because of when user press ctrl-c or another process tell something to this process. There are fix set of signals that can be sent to a process. signal are identified by i 5 min read
Program error signals Signals in computers are a way of communication between the process and the OS. When a running program undergoes some serious error then the OS sends a signal to the process and the process further may not execute. Some processes may have a signal handler that does some important tasks before the pr 3 min read
Socket Programming in C What is Socket Programming?Socket programming is a way of connecting two nodes on a network to communicate with each other. One socket(node) listens on a particular port at an IP, while the other socket reaches out to the other to form a connection. The server forms the listener socket while the cli 5 min read
_Generics Keyword in C The _Generic keyword in C is used to implement a generic code that can execute statements based on the type of arguments provided. It can be implemented with C macros to imitate function overloading. The _Generic keyword was first introduced in C11 Standard. Syntax of _Generic in C_Generic( (express 3 min read
Multithreading in C What is a Thread? A thread is a single sequence stream within a process. Because threads have some of the properties of processes, they are sometimes called lightweight processes. What are the differences between process and thread? Threads are not independent from each other unlike processes. As a 4 min read
C Programming Interview Questions (2024) At Bell Labs, Dennis Ritchie developed the C programming language between 1971 and 1973. C is a mid-level structured-oriented programming and general-purpose programming. It is one of the oldest and most popular programming languages. There are many applications in which C programming language is us 15+ min read
Commonly Asked C Programming Interview Questions | Set 1 What is the difference between declaration and definition of a variable/function Ans: Declaration of a variable/function simply declares that the variable/function exists somewhere in the program but the memory is not allocated for them. But the declaration of a variable/function serves an important 5 min read
Commonly Asked C Programming Interview Questions | Set 2 This post is second set of Commonly Asked C Programming Interview Questions | Set 1What are main characteristics of C language? C is a procedural language. The main features of C language include low-level access to memory, simple set of keywords, and clean style. These features make it suitable for 3 min read
Commonly Asked C Programming Interview Questions | Set 3 Q.1 Write down the smallest executable code? Ans. main is necessary for executing the code. Code is [GFGTABS] C void main() { } [/GFGTABS]Output Q.2 What are entry control and exit control loops? Ans. C support only 2 loops: Entry Control: This loop is categorized in 2 part a. while loop b. for loop 6 min read
Top 50 C Coding Interview Questions and Answers (2024) C is the most popular programming language developed by Dennis Ritchie at the Bell Laboratories in 1972 to develop the UNIX operating systems. It is a general-purpose and procedural programming language. It is faster than the languages like Java and Python. C is the most used language in top compani 15+ min read
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