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While executing an arithmetic operation the precedence of the operators in C as well as other programming language matters a lot because precedence determines the grouping of terms in an expression and decides how an expression is evaluated. For instance, the expression might be having various arithmetic operators like ‘+’, ‘-‘, or ‘*’; then how to know which part of the expression gets executed first.

Priority of Operators:

Let us take a look at the precedence of commonly used operators :

here the priority goes from high(* / %) to low(=):

Operator	Description
* / %	multiplication, division, modular division
+ –	addition, subtraction
=	assignment

Associativity of Operators:

When an expression contains two operators of equal priority the tie between them is settled using the associativity of the operators. Associativity can be of two types – left to right or right to left:

• Left to right associativity means that the left operand must be unambiguous i.e., it must not be involved in the evaluation of any other sub-expression.
• Likewise, in case of right to left associativity, the right operand must be ambiguous.

Category	Operator	Associativity
Postfix	() [] -> . ++ – –	Left to right
Unary	+ – ! ~ ++ – – (type)* & sizeof	Right to left
Multiplicative	* / %	Left to right
Additive	+ –	Left to right
Shift	<< >>	Left to right
Relational	< <= > >=	Left to right
Equality	== !=	Left to right
Bitwise AND	&	Left to right
Bitwise XOR	^	Left to right
Bitwise OR	|	Left to right
Logical AND	&&	Left to right
Logical OR	||	Left to right
Conditional	?:	Right to left
Assignment	= += -= *= /= %=>>= <<= &= ^= |=	Right to left
Comma	,	Left to right

Consider the expression-

a = 3 / 1 * 5 ;
output: 15

Here there is a tie between operators of same priority, that is between / and *. This tie is settled using the associativity of / and * since both / and * have L to R associativity and only / has unambiguous left operand ,therefore / is performed earlier.

note: also read about Variables & Constants in C & Operators in C.

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