Constants

Constants in the C language include:

• Integral constants

• Floating point constants

• Character constants

• Enumeration constants

Integral constants

Integral constants may be:

• Decimal:

  • Digits: ``0-9''.

  • The first digit may not be ``0'' (zero).

• Octal:

  • Digits: ``0-7''.

  • The first digit must be ``0'' (zero).

• Hexadecimal:

  • Digits: ``0-9'' plus letters ``a-f'' or ``A-F''. Letters correspond to decimal values 10-15.

  • Prefixed by ``0x'' or ``0'' (digit zero).

• Suffixes:

  All of the above can be suffixed to indicate type, as follows:

  Suffix	Type
  u or U	unsigned
  l or L	long
  both	unsigned long

Floating point constants

• Consist of integer part, decimal point, fraction part, an e or E, an optionally signed integer exponent, and a type suffix, one of f, F, l, or L. Each of these elements is optional; however one of the following must be present for the constant to be a floating point constant:

  • A decimal point (preceded or followed by a number).

  • An e with an exponent.

  • Any combination of the above. Examples:

       xxx  e exp
       xxx.
       .xxx
    

  Type determined by suffix; f or F indicates float, l or L indicateslong double, otherwise type is double.

Character constants

• One or more characters enclosed in single quotes, as in `x'.

• All character constants have type int.

• The value of a character constant is the numeric value of the character in the ASCII character set.

• A multiple-character constant that is not an escape sequence (see below) has a value derived from the numeric values of each character. For example, the constant `123' has a value of

  0

  '1'

  '2'

  '3'

  or 0x313233.

• Character constants may not contain the character ' or new-line. To represent these characters, and some others that may not be contained in the source character set, the compiler provides the following escape sequences:

Escape sequences

new-line	NL (LF)	\n	audible alert	BEL	\a
horizontal tab	HT	\t	question mark	?	\?
vertical tab	VT	\v	double quote	"	\"
backspace	BS	\b	octal escape	ooo	\ooo
carriage return	CR	\r	hexadecimal escape	hh	\xhh
formfeed	FF	\f	backslash	\	\\
single quote	'	\'

If the character following a backslash is not one of those specified, the compiler issues a warning and treat the backslash-character sequence as the character itself. Thus, '\\q' is treated as 'q'. However, if you represent a character this way, you run the risk that the character may be made into an escape sequence in the future, with unpredictable results. An explicit new-line character is invalid in a character constant and causes an error message.

• The octal escape consists of one to three octal digits.

• The hexadecimal escape consists of one or more hexadecimal digits

Wide characters and multibyte characters

• A wide character constant is a character constant prefixed by the letter L.

• A wide character has an external encoding as a multibyte character and an internal representation as the integral type wchar_t, defined in stddef.h.

• A wide character constant has the integral value for the multibyte character between single quote characters, as defined by the locale-dependent mapping function mbtowc.