# Expressions

< c‎ | language

An expression is a sequence of operators and their operands, that specifies a computation.

Expression evaluation may produce a result (e.g., evaluation of 2+2 produces the result 4), may generate side-effects (e.g. evaluation of printf("%d",4) sends the character '4' to the standard output stream), and may designate objects or functions.

## Contents

#### General

• value categories (lvalue, non-lvalue, function designator) classify expressions by their values
• order of evaluation of arguments and subexpressions specifies the order in which intermediate results are obtained

### Operators

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)

#### Conversions

• Implicit conversions take place when types of operands do not match the expectations of operators
• Casts may be used to explicitly convert values from one type to another.

### Primary expressions

The operands of any operator may be other expressions or they may be primary expressions (e.g. in 1+2*3, the operands of operator+ are the subexpression 2*3 and the primary expression 1).

Primary expressions are any of the following:

1) Constants and literals (e.g. 2 or "Hello, world")
2) Suitably declared identifiers (e.g. n or printf)

Any expression in parentheses is also classified as a primary expression: this guarantees that the parentheses have higher precedence than any operator.

#### Constants and literals

Constant values of certain types may be embedded in the source code of a C program using specialized expressions known as literals (for lvalue expressions) and constants (for non-lvalue expressions)

• integer constants are decimal, octal, or hexadecimal numbers of integer type.
• character constants are individual characters of type int suitable for conversion to a character type or of type char16_t, char32_t, (since C11)or wchar_t
• floating constants are values of type float, double, or long double
• string literals are sequences of characters of type char[], char16_t[], char32_t[], or wchar_t[] that represent null-terminated strings
• compound literals are values of struct, union, or array type directly embedded in program code

### Unevaluated expressions

The operands of the sizeof operator , the _Alignof operator, and the controlling expression of a generic selection, (since C11) are expressions that are not evaluated (unless they are VLAs) (since C99). Thus, size_t n = sizeof(printf("%d", 4)); does not perform console output.