An expression indicates how a collection of values are to be combined to perform a computation. When an expression is evaluated, the collection of values is determined, and the computation is performed, yielding a new value, the result. This value has a specific type, and a given expression will always yield values of the same type, hence we can say that the expression also has that type. It can also be given to sizeof to give the size of the type of the expression without actually evaluating it.

One of the simplest expressions is a constant. When evaluated, it yields that value, and its type is the type of that value. For example, 6 is a constant of type int, meaning and yielding the numeric value 6; 6L is a constant of type long, also meaning and yielding the numeric value 6. More complex expressions are possible by recursively combining one or more simpler expressions with one or more operators. The expressions combined with an operator are its operands. For example, 6 + 4 is an expression using the binary operator + to add its two operands 6 and 4 together.

An expression may refer to an object, meaning that, upon evaluation, its value should be retrieved and used in place of the reference. For example, 6 + x is an expression to compute the sum of the current value of the variable x and 6 (without changing x).

Most importantly, C expressions can have side-effects — the only way to change the value stored in an object, or perform some I/O. x = 6 is an expression which assigns the value 6 to the variable x as a side-effect.

expression

assignment-expression

expression , assignment-expression

assignment-expression

conditional-expression

unary-expression assignment-operator assignment-expression

assignment-operator

=

*=

/=

%=

+=

-=

<<=

>>=

&=

^=

|=

conditional-expression

logical-OR-expression

logical-OR-expression ? expression : conditional-expression

logical-OR-expression

logical-AND-expression

logical-OR-expression || logical-AND-expression

logical-AND-expression

inclusive-OR-expression

logical-AND-expression && inclusive-OR-expression

inclusive-OR-expression

exclusive-OR-expression

inclusive-OR-expression | exclusive-OR-expression

exclusive-OR-expression

AND-expression

exclusive-OR-expression ^ AND-expression

AND-expression

equality-expression

AND-expression & equality-expression

equality-expression

relational-expression

equality-expression == relational-expression

equality-expression != relational-expression

relational-expression

shift-expression

relational-expression < shift-expression

relational-expression > shift-expression

relational-expression <= shift-expression

relational-expression >= shift-expression

shift-expression

additive-expression

shift-expression << additive-expression

shift-expression >> additive-expression

additive-expression

multiplicative-expression

additive-expression + multiplicative-expression

additive-expression - multiplicative-expression

multiplicative-expression

cast-expression

multiplicative-expression * cast-expression

multiplicative-expression / cast-expression

multiplicative-expression % cast-expression

cast-expression

unary-expression

( type-name ) cast-expression

unary-expression

postfix-expression

++ unary-expression

Side-effects

-- unary-expression

Side-effects

unary-operator cast-expression

sizeof unary-expression

sizeof ( type-name )

_Alignof ( type-name )

unary-operator

&

*

+

-

~

!

postfix-expression

primary-expression

postfix-expression [ expression ]

Arrays

postfix-expression ( argument-expression-listopt )

Function calls

postfix-expression . identifier

Structures and Unions

postfix-expression -> identifier

Structures and Unions

postfix-expression ++

Side-effects

postfix-expression --

Side-effects

( type-name ) { initializer-list }

since C99; Structures

( type-name ) { initializer-list , }

since C99; Structures

primary-expression

identifier

constant

string-literal

( expression )

generic-selection

since C11

[: CX_LIMITED_RANGE]

[: FP_CONTRACT]