C Operator Precedence and Associativity

C Operator Precedence and Associativity

Precedence of Operators in C:

Operator precedence tells the order, in which operations are performed in an expression.

For example:

int n = 200 + 10 * 50;

Would the above expression be evaluated as (200 + 10) * 50 or 200 + (10 * 50). Would the addition be done first or multiplication. We all have studied BODMAS rule in mathematics, thus, we know that multiplication is done before addition. So the above expression would be solved like this given below-

Step 1 : 200 + (10 * 50)

Step 2 : 200 + 500

Result : 700

The precedence can be changed using parenthesis. The sub-expression in parenthesis would be evaluated first, no matter what operator has been used outside the sub-expression.

For example:

int n = (200 + 10) * 50;

This expression would be solved like this as given below-

Step 1 : 210 * 50;

Result : 10500

If nested parenthesis has been used, then innermost parenthesis would be evaluated first.

For example:

int n = 2 + (3 + (5 – 1)) * 4;

This expression would be evaluated like this as given below-

Step 1 : 2 + (3 + 4) * 4

Step 2 : 2 + 7 * 4

Step 3 : 2 + 28

Result : 30

If there is more than one parenthesis at different places in an expression, then sub-expressions in the parenthesis would be evaluated from left to right.

Associativity of Operators in C:

In C programming language, many operators can have same precedence or priority. If, in an expression, more than one operator have same precedence, the problem is resolved using the associativity of operators. All operators in C have either ‘Left to Right’ or ‘Right to Left associativity. It means, in an expression, if two operators have same precedence or priority, and their associativity is ‘Left to Right’, the operator, which comes first from left to right would be evaluated first. Let us understand this with an example given below-

int n = 5 + 3 * 4 / 2 – 1

This expression would be evaluated like this as given below-

Step 1 : 5 + (3 * 4) / 2 – 1

Step 2 : 5 + 12 / 2 – 1

Step 3 : 5 + (12 / 2 ) – 1

Step 4 : 5 + 6 – 1

Step 5 : (5 + 6) – 1

Step 6 : 11 – 1

Result : 10

In the above example, operators ‘*’ and ‘/’ have the same precedence. Their associativity is from left to right. Therefore, multiplication would take place before division. The same way, operators ‘+’ and ‘-‘ have same precedence, and associativity ‘Left to Right’. Hence, addition will be done before subtraction.

Again, precedence can be changed using parenthesis.

The precedence and associativity table of all operators in C has been given below for your quick reference. Operators are given from top to bottom in descending precedence or priority.

Precedence	Operator	Description	Associativity
1 Highest	++	Postfix increment	Left-to-right
	--	Postfix decrement
	()	Function call
	[]	Array subscripting
	.	Element selection by reference
	->	Element selection through pointer
2	++	Prefix increment	Right-to-left
	--	Prefix decrement
	+	Unary plus
	-	Unary minus
	!	Logical NOT
	~	Bitwise NOT (One's Complement)
	(type)	Type cast
	*	Indirection (dereference)
	&	Address-of
	sizeof	Size-of
3	*	Multiplication	Left-to-right
	/	Division
	%	Modulo (remainder)
4	+	Addition	Left-to-right
	-	Subtraction
5	<<	Bitwise  left shift	Left-to-right
	>>	Bitwise right shift
6	<	Less than	Left-to-right
	<=	Less than or equal to
	>	Greater than
	>=	Greater than or equal to
7	==	Equal to	Left-to-right
	!=	Not equal to
8	&	Bitwise AND	Left-to-right
9	^	Bitwise XOR (exclusive or)	Left-to-right
10	|	Bitwise OR (inclusive or)	Left-to-right
11	&&	Logical AND	Left-to-right
12	||	Logical OR	Left-to-right
13	?:	Ternary  conditional	Right-to-left
14	=	Direct assignment	Right-to-left
	+=	Assignment by sum
	-=	Assignment by difference
	*=	Assignment by product
	/=	Assignment by quotient
	%=	Assignment by remainder
	<<=	Assignment by bitwise left shift
	>>=	Assignment by bitwise right shift
	&=	Assignment by bitwise AND
	^=	Assignment by bitwise XOR
	|=	Assignment by bitwise OR
15 lowest	,	Comma	Left-to-right

This is all about precedence and associativity in C computer language. All operators will be described in later posts, wherever they are used.

If you are interested in how to create simple graphics in C, please visit my blog Graphics in C.