Expression C# là gì

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.

[edit] General

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

[edit] Operators

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)

• operator precedence defines the order in which operators are bound to their arguments
• alternative representations are alternative spellings for some operators

[edit] 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.

[edit] Other

• constant expressions can be evaluated at compile time and used in compile-time context (non-VLA (since C99)array sizes, static initializers, etc)

• generic selections can execute different expressions depending on the types of the arguments

• Floating-point expressions may raise exceptions and report errors as specified in math_errhandling
• The standard #pragmas FENV_ACCESS, FP_CONTRACT, and CX_LIMITED_RANGE as well as the floating-point evaluation precision and rounding direction control the way floating-point expressions are executed.

[edit] 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:

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

[edit] 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, or (since C11)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[], (since C11) or wchar_t[] that represent null-terminated strings

• compound literals are values of struct, union, or array type directly embedded in program code

[edit] Unevaluated expressions

The operands of the sizeof operator 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.

The operands of the _Alignof operator, the controlling expression of a generic selection, and size expressions of VLAs that are operands of _Alignof are also expressions that are not evaluated.

[edit] References

[edit] See also