A “character constant” is formed by enclosing a single character from the representable character set within single quotation marks (' '). Character constants are used to represent characters in the execution character set.
Syntax
character-constant :
'c-char-sequence'
L'c-char-sequence'
c-char-sequence :
c-char
c-char-sequence c-char
c-char :
Any member of the source character set except the single quotation mark ('), backslash (\), or newline character 
escape-sequence
escape-sequence :
simple-escape-sequence
octal-escape-sequence
hexadecimal-escape-sequence
simple-escape-sequence : one of
\a  \b  \f  \n  \r  \t  \v
\'  \"  \\  \?  
octal-escape-sequence :
\ octal-digit
\ octal-digit octal-digit
\ octal-digit octal-digit octal-digit
hexadecimal-escape-sequence :
\x hexadecimal-digit
hexadecimal-escape-sequence hexadecimal-digit