An identifier is an arbitrarily long sequence of digits, underscores, lowercase and uppercase Latin letters, and Unicode characters specified using \u and \U escape notation (since C99). A valid identifier must begin with a non-digit character (Latin letter, underscore, or Unicode non-digit character (since C99)). Identifiers are case-sensitive (lowercase and uppercase letters are distinct). It is implementation-defined if raw (not escaped) Unicode characters are allowed in identifiers. (since

Defined in header <stdlib.h> void ignore_handler_s( const char * restrict msg, void * restrict ptr, errno_t error ); (since C11) The function simply returns to the caller without performing any other action. A pointer to this function can be passed to set_constraint_handler_s to establish a runtime constraints violation handler that does nothing. As with all bounds-checked functions, ignore_handler_s is onl

Conditionally executes code. Used where code needs to be executed only if some condition is true. Syntax if ( expression ) statement_true (1) if ( expression ) statement_true else statement_false (2) Explanation expression must be an expression of any scalar type. If expression compares not equal to the integer zero, statement_true is executed. In the form (2), if expression compares equal to the integer zero, statement_false is executed. As with all other selection and ite

Usage if statement: as the declaration of the if statement

Transfers control unconditionally to the desired location. Used when it is otherwise impossible to transfer control to the desired location using conventional constructs. Syntax goto label ; label : statement Explanation The goto statement causes an unconditional jump (transfer of control) to the statement prefixed by the named label (which must appear in the same function as the goto statement), except when this jump would enter the scope of a variable-length array or anoth

Defined in header <complex.h> #define I /* unspecified */ (since C99) The I macro expands to either _Complex_I or _Imaginary_I. If the implementation does not support imaginary types, then the macro always expands to _Complex_I. A program may undefine and perhaps then redefine the macro I. Notes The macro is not named i, which is the name of the imaginary unit in mathematics, because the name i was already used in many C programs, e.g. as a loop counter variable. The mac

Defined in header <math.h> #define HUGE_VALF /*implementation defined*/ (since C99) #define HUGE_VAL /*implementation defined*/ #define HUGE_VALL /*implementation defined*/ (since C99) The HUGE_VALF, HUGE_VAL and HUGE_VALL macros expand to positive floating point constant expressions which compare equal to the values returned by floating-point functions and operators in case of overflow (see math_errhandling). Constant Explanation HUGE_VALF Expands to po

Defined in header <math.h> float hypotf( float x, float y ); (1) (since C99) double hypot( double x, double y ); (2) (since C99) long double hypotl( long double x, long double y ); (3) (since C99) Defined in header <tgmath.h> #define hypot( x, y ) (4) (since C99) 1-3) Computes the square root of the sum of the squares of x and y, without undue overflow or underflow at intermediate stages of the computation. 4) Type-generic macro:

Usage goto statement: as the declaration of the statement

Defined in header <wchar.h> wint_t getwchar(); (since C95) Reads the next wide character from stdin. Parameters (none). Return value the obtained wide character or WEOF if an error has occurred or the end of file reached. References C11 standard (ISO/IEC 9899:2011): 7.29.3.7 The getwchar function (p: 424) C99 standard (ISO/IEC 9899:1999): 7.24.3.7 The getwchar function (p: 369-370) See also getchar reads a character from stdin (function) fgetwcge