Operator Precedence and Associativity

Operator Precedence

• Operator precedence determines which operation is performed first in an expression.

• It refers to the order in which operators are evaluated in an expression. Operators with higher precedence are evaluated before operators with lower precedence.

For example:

• In the expression a + b * c, the multiplication operator (*) has higher precedence than the addition operator (+), so b * c is evaluated first, and then the result is added to a.

Operator Associativity

• Operators Associativity is used when two operators of same precedence appear in an expression.

• Determines the order in which operations with the same precedence are evaluated. There are two types of associativity: left-to-right and right-to-left.

Operators with left-to-right associativity are evaluated from left to right.

For example:

• In the expression a - b - c, the subtraction operator (-) has left-to-right associativity, so the expression is evaluated as (a - b) - c.

Operators with right-to-left associativity are evaluated from right to left.

For example:

• In the expression a = b = c, the assignment operator (=) has right-to-left associativity, so the expression is evaluated as a = (b = c).

Operator Precedence and Associativity Table

Following table shows the Operator Precedence and Associatvity in C:

Operator	Operator Name	Precedence	Associativity	Description
()	Function call	1	Left-to-right	Function call
[]	Array subscript	2	Left-to-right	Array subscript
.	Structure member access	3	Left-to-right	Structure member access
->	Structure pointer member access	4	Left-to-right	Structure pointer member access
++	postfix increment	5	Left-to-right	Increments the value of the operand by 1 after the expression is evaluated
--	postfix decrement	5	Left-to-right	Decrements the value of the operand by 1 after the expression is evaluated
++	prefix increment	6	Right-to-left	Increments the value of the operand by 1 before the expression is evaluated
--	prefix decrement	6	Right-to-left	Decrements the value of the operand by 1 before the expression is evaluated
+	unary plus	7	Right-to-left	Unary plus operator
-	unary minus	7	Right-to-left	Unary minus operator
!	logical NOT	8	Right-to-left	Logical NOT operator
~	bitwise NOT	8	Right-to-left	Bitwise NOT operator
*	dereference	9	Right-to-left	Dereference operator
&	address-of	9	Right-to-left	Address-of operator
sizeof	sizeof	9	Right-to-left	Size
*	multiplication	10	Left-to-right	Multiplication operator
/	division	10	Left-to-right	Division operator
%	modulo	10	Left-to-right	Modulo operator
+	addition	11	Left-to-right	Addition operator
-	subtraction	11	Left-to-right	Subtraction operator
<<	bitwise left shift	12	Left-to-right	Bitwise left shift operator
>>	bitwise right shift	12	Left-to-right	Bitwise right shift operator
<	less than	13	Left-to-right	Less than operator
<=	less than or equal to	13	Left-to-right	Less than or equal to operator
>	greater than	13	Left-to-right	Greater than operator
>=	greater than or equal to	13	Left-to-right	Greater than or equal to operator
==	equal to	14	Left-to-right	Equal to operator
!=	not equal to	14	Left-to-right	Not equal to operator
&	bitwise AND	15	Left-to-right	Bitwise AND operator
^	bitwise XOR	16	Left-to-right	Bitwise XOR operator
"	"	bitwise OR	17	Left-to-right
&&	logical AND	18	Left-to-right	Logical AND operator
"		"	logical OR	19
?:	ternary operator	20	Right-to-left	ternary operator
"="	assignment	21	Right-to-left	assignment
+=	addition assignment	21	Right-to-left	Ternary operator (conditional operator)
-=	subtraction assignment	21	Right-to-left	Assignment operator
*=	multiplication assignment	21	Right-to-left	Addition assignment operator
/=	division assignment	21	Right-to-left	Subtraction assignment operator
%=	modulo assignment	21	Right-to-left	Multiplication assignment operator
&=	bitwise AND assignment	21	Right-to-left	Division assignment operator
^=	bitwise XOR assignment	21	Right-to-left	Modulo assignment operator
	=	bitwise OR assignment	21	Right-to-left
<<=	bitwise left shift assignment	21	Right-to-left	Bitwise left shift assignment operator
>>=	bitwise right shift assignment	21	Right-to-left	Bitwise right shift assignment operator
,	comma operator	22	Left-to-right	Comma operator

Operator Precedence Example

Below program shows the operator precedence in C:

#include <stdio.h>

int main() {
    int x = 10;
    int y = 20;
    int z = 30;

    printf("x + y * z = %d\n", x + y * z);  // x + y * z = 210
    printf("x * y + z = %d\n", x * y + z);  // x * y + z = 650
    printf("x / y + z = %d\n", x / y + z);  // x / y + z = 30
    printf("x / (y + z) = %d\n", x / (y + z));  // x / (y + z) = 0
    printf("x / y * z = %d\n", x / y * z);  // x / y * z = 0
    printf("(x + y) * z = %d\n", (x + y) * z);  // (x + y) * z = 900
    return 0;
}

Output:

Explanation

• In the first line of the program, the multiplication is done first, and then the addition.
• In the second line of the program, the multiplication is done first, and then the addition.
• In the third line of the program, the division is done first, and then the addition.
• In the fourth line of the program, the parentheses are used to change the order of evaluation, so the addition is done first, and then the division.
• In the fifth line of the program, the division is done first, and then the multiplication
• In the sixth line, the addition is done first, and then the multiplication.

Operator Associativity Example

Below program shows the Operator Associativity in C:

#include <stdio.h>

int main() {
    int x = 10;
    int y = 20;
    int z = 30;

    printf("x - y - z = %d\n", x - y - z);  // x - y - z = -40
    printf("x / y / z = %d\n", x / y / z);  // x / y / z = 0
    printf("x - (y - z) = %d\n", x - (y - z));  // x - (y - z) = 20
    printf("(x / y) / z = %d\n", (x / y) / z);  // (x / y) / z = 0
    printf("x / (y / z) = %d\n", x / (y / z));  // x / (y / z) = 2
    return 0;
}

Output:

Explanation

• In the first line of the program, the subtraction is done from left to right, so the value of x is subtracted from the value of y, and then the value of z is subtracted from the result.
• In the second line of the program, the division is done from left to right, so the value of x is divided by the value of y, and then the result is divided by the value of z.
• In the third line of the program, the parentheses are used to change the order of evaluation, so the subtraction is done first, and then the value of x is subtracted from the result.
• In the fourth line of the program, the division inside the parenthesis is done first, and then the division outside the parenthesis is done.
• In the fifth line, the division inside the parenthesis is done first, and then the division outside the parenthesis is done.

Best Practices

Lastly, Below are some of the best practices when dealing with Operator Precedence and Associativity in your programming:

• Use parentheses: Always use parentheses to indicate the intended order of evaluation, making your code easier to read and understand.

• Default operator precedence and associativity: Always be aware of the default operator precedence and associativity of C programming language, and use them consistently throughout your code.

• Whitespaces around operators: Use whitespaces around operators to make the code more readable and easy to understand.

• Multiple operators with the same precedence: Avoid using multiple operators with the same precedence in the same line of code, as it can be confusing.

• Thoroughly test your code: Thoroughly test your code with a variety of inputs and edge cases to ensure that it is robust and reliable.

• Document complex expressions: Always document any non-standard or complex expressions in your code to help other developers understand the intended behavior. When in doubt, use parentheses to make the order of operations explicit.

• Follow the conventions: Follow the conventions of the language, if any, to make the code easy to understand by other developers who might read it in the future.