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Operator precedence determines the sequence in which operators in an expression are executed. This order of precedence can affect the result of an expression substantially. For example, suppose you are to process job applications and you want to only accept applicants who are 25 or older and have graduated from Harvard or Yale. Here’s the age condition you can represent by this conditional expression:

Age >= 25

Suppose that you represent graduation by the variables Yale and Harvard, which may be true or false. Now you can write the condition as follows:

Age >= 25 && Harvard || Yale

Unfortunately, this will result in protest because you will now accept Yale graduates who are under 25. In fact, this statement will accept Yale graduates of any age. But if you’re from Harvard, you must be 25 or over to be accepted. Because of operator precedence, this expression is effectively the following:

(Age >= 25 && Harvard) || Yale

So now you take anybody at all from Yale. I’m sure those wearing a Y-front sweatshirt will claim that this is as it should be, but what you really meant was this:

Age >= 25 && (Harvard || Yale)

Because of operator precedence, you must put the parentheses in the expression to force the order of operations to be what you want.

In general, the precedence of the operators in an expression determines whether it is necessary for you to put parentheses in to get the result you want, but if you are unsure of the precedence of the operators you are using, it does no harm to put the parentheses in. Below table shows the order of precedence for all the operators in C, from highest at the top to lowest at the bottom.

Operator Precedence Table

Description	Operator	Associativity
Function Expression	( )	Left to Right
Array Expression	[ ]	Left to Right
Structure operator	->	Left to Right
Structure operator	.	Left to Right
Unary minus	-	Right to left
Increment/Decrement	++ --	Right to left
One’s compliment	~	Right to left
Negation	!	Right to left
Address of	&	Right to left
Value of address	*	Right to left
Type cast	( type )	Right to left
Size in bytes	sizeof	Right to left
Multiplication	*	Left to Right
Division	/	Left to Right
Modulus	%	Left to Right
Addition	+	Left to Right
Subtraction	-	Left to Right
Left shift	<<	Left to Right
Right shift	>>	Left to Right
Less than	<	Left to Right
Less than or equal to	<=	Left to Right
Greater than	>	Left to Right
Greater than or equal to	>=	Left to Right
Equal to	==	Left to Right
Not equal to	!=	Left to Right
Bitwise AND	&	Left to Right
Bitwise exclusive OR	^	Left to Right
Bitwise inclusive OR	|	Left to Right
Logical AND	&&	Left to Right
Logical OR	||	Left to Right
Conditional	? :	Right to left
Assignment	=  *=  /=   %= +=  -=  &= ^=  |= <<=  >>=	Right to left  Right to left  Right to left  Right to left  Right to left
Comma	,	Right to left

For better understanding

Common operators
assignment	increment decrement	arithmetic	logical	comparison	member access	other
a = b a += b a -= b a *= b a /= b a %= b a &= b a |= b a ^= b a <<= b a >>= b	++a --a a++ a--	+a -a a + b a - b a * b a / b a % b ~a a & b a | b a ^ b a << b a >> b	!a a && b a || b	a == b a != b a < b a > b a <= b a >= b	a[b] *a &a a->b a.b	a(...) a, b (type) a ? : sizeof _Alignof (since C11)

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